Chemistry - ACT Science
Card 0 of 4048
Two scientists wanted to test the solubility of different substances. Solubility is a measure of how many moles of a given substance (known as the solute) can dissolve in a given volume of another substance (known as the solvent). The solvent can also be thought of as the substance present in greater amount, while the solute can be seen as the substance present in lesser amount. The scientists performed the following experiments to investigate this property.
Experiment 1
The scientists tested the number of moles of several substances that could be completely dissolved in 
of water at various temperatures. They made their solutions by slowly adding amounts of each substance to beakers sitting on a hot plate containing water and a stirring rod until no more of the substance dissolved in the solution. The beakers were weighed before and after the additions and the difference in mass was calculated to be the added mass of the substance. The researchers then calculated the number of moles that dissolved for each trial using the molecular mass and the recorded mass for each trial. Results are recorded in Table 1.
Table 1
Experiment 2
In this experiment, the scientists wanted to test the solubility of 
in a variety of liquids at several temperatures. Their procedure was similar to that of Experiment 1, but with a range of liquids and only one solid. The results are compiled in Table 2.
Table 2
Which of the following best explains the relationship between temperature and solubility of 
?
Two scientists wanted to test the solubility of different substances. Solubility is a measure of how many moles of a given substance (known as the solute) can dissolve in a given volume of another substance (known as the solvent). The solvent can also be thought of as the substance present in greater amount, while the solute can be seen as the substance present in lesser amount. The scientists performed the following experiments to investigate this property.
Experiment 1
The scientists tested the number of moles of several substances that could be completely dissolved in
Table 1
Experiment 2
In this experiment, the scientists wanted to test the solubility of
Table 2
Which of the following best explains the relationship between temperature and solubility of
This question doesn't tell us where to look, but it tells us we need to be concerned with solubility of 
. Experiment 1 is the only place where 
is mentioned, so begin there. In Table 1, the entries for moles of 
are highest at 
, and lower for increasing temperature. This means that temperature and solubility are indirectly related; as one increases, the other decreases. Thus, our correct answer is, "As temperature decreases, solubility of 
increases," because our solubility is highest at lower temperatures.
This question doesn't tell us where to look, but it tells us we need to be concerned with solubility of
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Given that all of the following are true, which of the following, if found, provides the strongest evidence against Scientist 2's hypothesis?
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Given that all of the following are true, which of the following, if found, provides the strongest evidence against Scientist 2's hypothesis?
Scientist 2 states that acid is required for rust to form. Because acid releases H+ ions—which, according to Scientist 2, are involved in the production of rust—we should expect that adding more acid to a solution will speed up the formation of rust. If, however, adding citric acid actually reverses rusting or removes rust (causing a piece of iron to become shiny again), this would suggest that Scientist 2's explanation is wrong.
Scientist 2 also states that acid may be formed in a solution because of atmospheric carbon dioxide dissolving in the water or because of impurities in a piece of iron. So, rust may form even when no acid is directly added to water. It is also possible that different amounts of impurities in different pieces of iron cause them to rust at different rates. This is why some of the other answers are not correct.
Scientist 2 states that acid is required for rust to form. Because acid releases H+ ions—which, according to Scientist 2, are involved in the production of rust—we should expect that adding more acid to a solution will speed up the formation of rust. If, however, adding citric acid actually reverses rusting or removes rust (causing a piece of iron to become shiny again), this would suggest that Scientist 2's explanation is wrong.
Scientist 2 also states that acid may be formed in a solution because of atmospheric carbon dioxide dissolving in the water or because of impurities in a piece of iron. So, rust may form even when no acid is directly added to water. It is also possible that different amounts of impurities in different pieces of iron cause them to rust at different rates. This is why some of the other answers are not correct.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Lye (sodium hydroxide) is a base that neutralizes acids. Suppose that lye is added to water in which an iron pipe has been immersed. According to Scientist 2, the pipe's rate of rusting will most likely __________.
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Lye (sodium hydroxide) is a base that neutralizes acids. Suppose that lye is added to water in which an iron pipe has been immersed. According to Scientist 2, the pipe's rate of rusting will most likely __________.
According to Scientist 2, acid is needed for rust to form. However, the question tells us that lye neutralizes acids. So, if lye is added to the solution, the solution will become less acidic, and rust will not form, or form at a slower rate.
According to Scientist 2, acid is needed for rust to form. However, the question tells us that lye neutralizes acids. So, if lye is added to the solution, the solution will become less acidic, and rust will not form, or form at a slower rate.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
An iron nail is placed in an unsealed test tube filled with water. No other substances are added to the water. When the nail is removed after an extended period of time, it is covered by rust. According the Scientist 2, the nail most likely rusted because __________.
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
An iron nail is placed in an unsealed test tube filled with water. No other substances are added to the water. When the nail is removed after an extended period of time, it is covered by rust. According the Scientist 2, the nail most likely rusted because __________.
According to Scientist 2, acid is needed for rust to form. However, Scientist 2 also tells us that acid may form spontaneously when carbon dioxide from the air dissolves in water and reacts to form carbonic acid. In this experiment, because it was observed that the iron nail did rust, some acid must have been in the water. This acid might have been carbonic acid produced from carbon dioxide, or other acids produced from impurities contained in the iron nail. Out of these two options, the only one listed as a possible answer choice is the situation involving carbon dioxide and carbonic acid.
According to Scientist 2, acid is needed for rust to form. However, Scientist 2 also tells us that acid may form spontaneously when carbon dioxide from the air dissolves in water and reacts to form carbonic acid. In this experiment, because it was observed that the iron nail did rust, some acid must have been in the water. This acid might have been carbonic acid produced from carbon dioxide, or other acids produced from impurities contained in the iron nail. Out of these two options, the only one listed as a possible answer choice is the situation involving carbon dioxide and carbonic acid.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Sodium hydroxide (NaOH) is a compound which dissociates into Na+ and OH- ions in solution. Suppose that sodium hydroxide is added to water in which a piece of iron has been immersed. It is then observed that the rate at which rust forms on the iron increases. Scientist 1 would most likely explain this result by saying that __________.
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Sodium hydroxide (NaOH) is a compound which dissociates into Na+ and OH- ions in solution. Suppose that sodium hydroxide is added to water in which a piece of iron has been immersed. It is then observed that the rate at which rust forms on the iron increases. Scientist 1 would most likely explain this result by saying that __________.
According to Scientist 1, hydroxide (OH-) ions are one of the precursors involved in the formation of rust. Since sodium hydroxide dissociates into Na+ and OH- ions, adding sodium hydroxide to a solution would increase the concentration of OH- ions. If Scientist 1 is right, this should also speed up or facilitate the formation of iron hydroxide, which should then turn into rust.
According to Scientist 1, hydroxide (OH-) ions are one of the precursors involved in the formation of rust. Since sodium hydroxide dissociates into Na+ and OH- ions, adding sodium hydroxide to a solution would increase the concentration of OH- ions. If Scientist 1 is right, this should also speed up or facilitate the formation of iron hydroxide, which should then turn into rust.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
According to Scientist 1, which of the following conditions will result in the least rapid formation of rust?
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
According to Scientist 1, which of the following conditions will result in the least rapid formation of rust?
Scientist 1 states that increasing the surface area of iron and increasing the ambient temperature both speed up the formation of rust. Additionally, she says that salt acts as a catalyst for rust formation, meaning that adding salt to a solution also speeds up the formation of rust. Because this question asks us for the situation under which rust will form least rapidly, the correct answer is the one in which iron has a smaller surface area (the iron strip) and is placed in cooler (5°C)water.
Scientist 1 states that increasing the surface area of iron and increasing the ambient temperature both speed up the formation of rust. Additionally, she says that salt acts as a catalyst for rust formation, meaning that adding salt to a solution also speeds up the formation of rust. Because this question asks us for the situation under which rust will form least rapidly, the correct answer is the one in which iron has a smaller surface area (the iron strip) and is placed in cooler (5°C)water.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Given that the explanation of Scientist 2 is correct, which of the following conditions, if any, will result in the formation of rust?
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Given that the explanation of Scientist 2 is correct, which of the following conditions, if any, will result in the formation of rust?
According to Scientist 2, water must contain oxygen and acid in order for rust to form. However, Scientist 2 says that even when no acid is directly added to water, carbon dioxide from the air can react with water to form carbonic acid. Oxygen can also dissolve from the air into the water. So, if an iron pot is placed in an unsealed container of water, both oxygen and carbon dioxide from the atmosphere can enter the water. This creates conditions under which rust can form.
According to Scientist 2, water must contain oxygen and acid in order for rust to form. However, Scientist 2 says that even when no acid is directly added to water, carbon dioxide from the air can react with water to form carbonic acid. Oxygen can also dissolve from the air into the water. So, if an iron pot is placed in an unsealed container of water, both oxygen and carbon dioxide from the atmosphere can enter the water. This creates conditions under which rust can form.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Bromothymol blue is a pH indicator that is yellow in acidic solutions and blue in basic solutions. When bromothymol blue is added to a solution, it remains blue. A piece of iron is then immersed in this solution. Given that the explanation of Scientist 2 is correct, which of the following is most likely to occur?
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
Bromothymol blue is a pH indicator that is yellow in acidic solutions and blue in basic solutions. When bromothymol blue is added to a solution, it remains blue. A piece of iron is then immersed in this solution. Given that the explanation of Scientist 2 is correct, which of the following is most likely to occur?
Scientist 2 states that rusting is caused by attack by an acid. If he is right, rust can form in acidic solutions, but will not form in basic solutions. This question tells us that the blue color of bromothymol blue shows that a solution is basic. Since the bromothymol blue keeps its blue color, we know that the solution in the question is basic. So, rust will most likely not be formed.
Scientist 2 states that rusting is caused by attack by an acid. If he is right, rust can form in acidic solutions, but will not form in basic solutions. This question tells us that the blue color of bromothymol blue shows that a solution is basic. Since the bromothymol blue keeps its blue color, we know that the solution in the question is basic. So, rust will most likely not be formed.
Compare your answer with the correct one above
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
In an experiment, oxygen is removed from water by boiling the water. This water is then poured into a flask, and a piece of iron is immersed in the water. Excess air is pumped out from the flask and replaced with helium (He). Then the flask is sealed. After an extended period of time, a reddish-orange substance is observed on the surface of the iron.
Given that Scientist 2 is correct, which of the following most likely describes the identity of the reddish-orange substance?
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
In an experiment, oxygen is removed from water by boiling the water. This water is then poured into a flask, and a piece of iron is immersed in the water. Excess air is pumped out from the flask and replaced with helium (He). Then the flask is sealed. After an extended period of time, a reddish-orange substance is observed on the surface of the iron.
Given that Scientist 2 is correct, which of the following most likely describes the identity of the reddish-orange substance?
The explanation of Scientist 2 requires that oxygen be dissolved in water in order for rust to form. According to Scientist 2, free iron (Fe2+) ions react with dissolved atmospheric oxygen to form iron oxide. However, in this question, dissolved oxygen is removed from the water by boiling, and no additional oxygen is allowed to diffuse into the water, because the air is replaced with helium. Because no oxygen can get into the water, it would be impossible for rust to form. So, the reddish-orange substance must be another compound instead of rust.
The explanation of Scientist 2 requires that oxygen be dissolved in water in order for rust to form. According to Scientist 2, free iron (Fe2+) ions react with dissolved atmospheric oxygen to form iron oxide. However, in this question, dissolved oxygen is removed from the water by boiling, and no additional oxygen is allowed to diffuse into the water, because the air is replaced with helium. Because no oxygen can get into the water, it would be impossible for rust to form. So, the reddish-orange substance must be another compound instead of rust.
Compare your answer with the correct one above
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
Assuming that both students' statements are correct in describing the ideal gas law, how would we then describe the effects of molecule size and IMFAs on a gas's volume?
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
Assuming that both students' statements are correct in describing the ideal gas law, how would we then describe the effects of molecule size and IMFAs on a gas's volume?
The correct answer is that a greater IMFA would lead to a smaller volume and a greater molecule size would lead to larger volume. Student 2's statement about IMFAs shows us that greater attraction between molecules would lead to a smaller volume than predicted by the ideal gas law. Student 1's claim is a little bit more subtle. Student 1 says that one of the assumptions about the ideal gas law is that we are treating molecule size as negligible compared to the space between each molecule. If we are ignoring the volume these molecules take up, then a gas with very large molecules may leave this assumption to be invalid. Therefore, if we consider the volume that gas molecules occupy, we can assume the volume would be greaterthan what would be predicted by ignoring the volume they occupy.
The correct answer is that a greater IMFA would lead to a smaller volume and a greater molecule size would lead to larger volume. Student 2's statement about IMFAs shows us that greater attraction between molecules would lead to a smaller volume than predicted by the ideal gas law. Student 1's claim is a little bit more subtle. Student 1 says that one of the assumptions about the ideal gas law is that we are treating molecule size as negligible compared to the space between each molecule. If we are ignoring the volume these molecules take up, then a gas with very large molecules may leave this assumption to be invalid. Therefore, if we consider the volume that gas molecules occupy, we can assume the volume would be greaterthan what would be predicted by ignoring the volume they occupy.
Compare your answer with the correct one above
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
An experiment was carried out that measured the volumes of two very small quantities of gases, hydrogen and tetrachloromethane. Both gases have a dipole moment of zero, meaning they do not exhibit intermolecular forces of attraction. Hydrogen is the lightest known gas, while tetrachloromethane is much heavier and therefore has much larger molecules.
The experiment yielded the following result: the same number of hydrogen molecules occupied a slightly different volume than an equivalent quantity of tetrachloromethane. This remained true only for small quantities of both gases.
What does this experimental data mean with regard to the opinions of the two students above?
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
An experiment was carried out that measured the volumes of two very small quantities of gases, hydrogen and tetrachloromethane. Both gases have a dipole moment of zero, meaning they do not exhibit intermolecular forces of attraction. Hydrogen is the lightest known gas, while tetrachloromethane is much heavier and therefore has much larger molecules.
The experiment yielded the following result: the same number of hydrogen molecules occupied a slightly different volume than an equivalent quantity of tetrachloromethane. This remained true only for small quantities of both gases.
What does this experimental data mean with regard to the opinions of the two students above?
The answer is that this information supports the opinion of Student 1. This can be tricky because supporting Student 1 does not necessarily mean refuting S_tudent 2's statements. This is an important distinction in the scientific process. Student 2 simply failed to mention molecule size in the given description of the ideal gas law's assumptions. This new information does not then refute the statements that Student 2 did make, since Student 2 did not mention molecular size; however, this information does appear to suggest that large differences in molecular size does affect measured volume when working with small quantities of gas. Indeed, this is consistent with Student 1's description, which emphasized that treating molecule size as negligible is a general assumption._ Therefore, it may not hold true at small volumes where space between molecules may not be enough to make the assumption.
It should be noted that this in fact is how gases work. They tend to deviate from ideal behavior only at high pressures, low temperatures, and small volumes.
The answer is that this information supports the opinion of Student 1. This can be tricky because supporting Student 1 does not necessarily mean refuting S_tudent 2's statements. This is an important distinction in the scientific process. Student 2 simply failed to mention molecule size in the given description of the ideal gas law's assumptions. This new information does not then refute the statements that Student 2 did make, since Student 2 did not mention molecular size; however, this information does appear to suggest that large differences in molecular size does affect measured volume when working with small quantities of gas. Indeed, this is consistent with Student 1's description, which emphasized that treating molecule size as negligible is a general assumption._ Therefore, it may not hold true at small volumes where space between molecules may not be enough to make the assumption.
It should be noted that this in fact is how gases work. They tend to deviate from ideal behavior only at high pressures, low temperatures, and small volumes.
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Nanoparticles are fabricated by vigorously mixing the constituent components of the particle in solution. A scientist has four different compositions that she has tested: Composition A, Composition B, Composition C, and Composition D. All of these compositions were observed under similar laboratory conditions using different mixing times. The average particle size for each scenario was recorded in the provided table.
The scientist wants to make the nanoparticles that are all the same size. If the minimum mixing time required to make nanoparticles is 
, then how can this be achieved?
Nanoparticles are fabricated by vigorously mixing the constituent components of the particle in solution. A scientist has four different compositions that she has tested: Composition A, Composition B, Composition C, and Composition D. All of these compositions were observed under similar laboratory conditions using different mixing times. The average particle size for each scenario was recorded in the provided table.
The scientist wants to make the nanoparticles that are all the same size. If the minimum mixing time required to make nanoparticles is
A method to solve this question is the process of elimination. Increasing the mixing time after 
did not change particle size; thus, this implies that increasing the mixing time past 
will not decrease particle size. Therefore, the choice that suggests increasing the mixing times for Compositions A, B, and C, while mixing Composition D for 
is eliminated. Mixing Composition A for 
, while mixing all other Compositions for 
will not produce particles of the same size either. This is supported by looking at the 
column and noticing that the nanoparticles possess different sizes. Likewise, choosing to mix all of the particles for 
would be incorrect because this produces particles of different sizes as seen in the 
column. As a result, the choices of "It cannot be determined from the given information" and "It cannot be achieved" are left. The question can be determined using the given information; thus, the choice stating otherwise can be eliminated. This is possible to determine because the largest particle radius that Composition D can achieve is at 
, which is 
while the smallest particle radius that Composition A can achieve, 
, is at 
, 
, or 
(there is no significant difference in radii size after 
). The smallest radius for Composition A is much larger than the largest possible radius for Composition D; therefore, the scientist's goal of uniform size is unachievable.
A method to solve this question is the process of elimination. Increasing the mixing time after
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The table lists some of the properties of row 2 elements in the periodic table.
What conclusion can be drawn from the data in regards to atomic radius in row 2 elements on the periodic table?
The table lists some of the properties of row 2 elements in the periodic table.
What conclusion can be drawn from the data in regards to atomic radius in row 2 elements on the periodic table?
From studying the table it can be seen that the elements with the top two highest atomic radii are metals. As the atomic radius decreases elements are non-metals.
From studying the table it can be seen that the elements with the top two highest atomic radii are metals. As the atomic radius decreases elements are non-metals.
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Two scientists wanted to test the solubility of different substances. Solubility is a measure of how many moles of a given substance (known as the solute) can dissolve in a given volume of another substance (known as the solvent). The solvent can also be thought of as the substance present in greater amount, while the solute can be seen as the substance present in lesser amount. The scientists performed the following experiments to investigate this property.
Experiment 1
The scientists tested the number of moles of several substances that could be completely dissolved in of water at various temperatures. They made their solutions by slowly adding amounts of each substance to beakers sitting on a hot plate containing water and a stirring rod until no more of the substance dissolved in the solution. The beakers were weighed before and after the additions and the difference in mass was calculated to be the added mass of the substance. The researchers then calculated the number of moles that dissolved for each trial using the molecular mass and the recorded mass for each trial. Results are recorded in Table 1.
Table 1
Experiment 2
In this experiment, the scientists wanted to test the solubility of in a variety of liquids at several temperatures. Their procedure was similar to that of Experiment 1, but with a range of liquids and only one solid. The results are compiled in Table 2.
Table 2
Suppose the scientists conducted a third experiment in which they dissolved 
in 
of methanol at 
. Which of the following might have been the number of grams dissolved?
Two scientists wanted to test the solubility of different substances. Solubility is a measure of how many moles of a given substance (known as the solute) can dissolve in a given volume of another substance (known as the solvent). The solvent can also be thought of as the substance present in greater amount, while the solute can be seen as the substance present in lesser amount. The scientists performed the following experiments to investigate this property.
Experiment 1
The scientists tested the number of moles of several substances that could be completely dissolved in
Table 1
Experiment 2
In this experiment, the scientists wanted to test the solubility of
Table 2
Suppose the scientists conducted a third experiment in which they dissolved
This question requires some careful reading and extrapolation. We want to find the number of grams dissolved in of methanol at . Experiment 2 is the only place in which methanol is mentioned, so start there.
In experiment two, we need two details to guide us.
-
of each liquid was used.
-
The highest temperature tested for methanol was 
, and at that temperature, 
dissolved.
So, the scientists had 
at 
C in 50 mL. We want to find how many grams will dissolve at 
C in 100 mL. We know that as temperature is increased, more grams of 
dissolve in the same amount of methanol.
So, we can eliminate any answers lower than or equal to 
. This leaves us with one answer choice, the correct one:
This question requires some careful reading and extrapolation. We want to find the number of grams dissolved in
In experiment two, we need two details to guide us.
-
-
The highest temperature tested for methanol was
So, the scientists had
So, we can eliminate any answers lower than or equal to
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A student performed the following procedures to study various photosynthetic pigments (light-absorbing chemicals) in tree leaves and the wavelengths of light they absorb.
Experiment 1:
The student obtained samples of leaves from oaks, maples, ashes, sycamores, and poplars. Each leaf sample was ground separately with a mortar and pestle to release the pigments, and then each sample was suspended in water to make a colored solution of the pigment. The student then measured the absorption spectrum (a graph of how much light is absorbed by a pigment at varying wavelengths of light) of each solution in a device called a spectrophotometer. The setup of a spectrophotometer is shown below in Diagram 1.
The light source emits white light, which is split into its various wavelengths by the prism. Next, a slit, which can be moved up or down to select a particular wavelength, is used to transmit just a single wavelength to the sample. The sample absorbs a fraction of this light that is characteristic to the pigment in the sample, and the rest is transmitted to the detector for a readout. Using the spectrophotometer, the student found the λmax (the wavelength of light in nanometers (nm) that the pigment absorbs most intensely, for each sample) and recorded the results in Table 1. Table 1 also shows the transmittance and absorbance values at λmax. Transmittance, T, is defined as the fraction of light, expressed as a decimal, which passes through the sample. Absorbance, A, is given by:
A = –log(T) or 10–A = T
Experiment 2:
A student is given a leaf from an unknown source. She crushes and extracts the pigment according to the procedure in Experiment 1. Measuring the absorbance spectrum in the spectrophotometer produces the following readout, shown in Diagram 2.
Diagram 2
During the experiment, the student finds the mechanism that moves the slit up and down has stopped functioning. Which of the following will result from this problem?
A student performed the following procedures to study various photosynthetic pigments (light-absorbing chemicals) in tree leaves and the wavelengths of light they absorb.
Experiment 1:
The student obtained samples of leaves from oaks, maples, ashes, sycamores, and poplars. Each leaf sample was ground separately with a mortar and pestle to release the pigments, and then each sample was suspended in water to make a colored solution of the pigment. The student then measured the absorption spectrum (a graph of how much light is absorbed by a pigment at varying wavelengths of light) of each solution in a device called a spectrophotometer. The setup of a spectrophotometer is shown below in Diagram 1.
The light source emits white light, which is split into its various wavelengths by the prism. Next, a slit, which can be moved up or down to select a particular wavelength, is used to transmit just a single wavelength to the sample. The sample absorbs a fraction of this light that is characteristic to the pigment in the sample, and the rest is transmitted to the detector for a readout. Using the spectrophotometer, the student found the λmax (the wavelength of light in nanometers (nm) that the pigment absorbs most intensely, for each sample) and recorded the results in Table 1. Table 1 also shows the transmittance and absorbance values at λmax. Transmittance, T, is defined as the fraction of light, expressed as a decimal, which passes through the sample. Absorbance, A, is given by:
A = –log(T) or 10–A = T
Experiment 2:
A student is given a leaf from an unknown source. She crushes and extracts the pigment according to the procedure in Experiment 1. Measuring the absorbance spectrum in the spectrophotometer produces the following readout, shown in Diagram 2.
Diagram 2
During the experiment, the student finds the mechanism that moves the slit up and down has stopped functioning. Which of the following will result from this problem?
The description of the spectrophotometer in Experiment 1 states that the purpose of the slit is to be able to select a single wavelength of light. This wavelength can be chosen by moving the slit up or down. Thus, if it cannot move up or down, it can only select the wavelength of light it is stuck on, and can no longer scan different wavelengths of light to pass through the sample.
Finding the transmittance is governed by the function of the detector, finding the absorbance is governed by a mathematical transformation of the transmittance value as shown by the equation in Experiment 1, and the splitting of white light into various wavelengths is governed by the function of the prism. Thus, the three other answers are incorrect.
The description of the spectrophotometer in Experiment 1 states that the purpose of the slit is to be able to select a single wavelength of light. This wavelength can be chosen by moving the slit up or down. Thus, if it cannot move up or down, it can only select the wavelength of light it is stuck on, and can no longer scan different wavelengths of light to pass through the sample.
Finding the transmittance is governed by the function of the detector, finding the absorbance is governed by a mathematical transformation of the transmittance value as shown by the equation in Experiment 1, and the splitting of white light into various wavelengths is governed by the function of the prism. Thus, the three other answers are incorrect.
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A student wanted to study the kinetics, or rates of a chemical reaction based on the concentrations of its reactants and products, of the reaction shown below.
This reaction is easy to monitor using a spectrophotometer, which measures how much light of a particular wavelength is absorbed by a solution. The deep purple potassium permanganate, or 
, absorbs light of a 550 nm wavelength in proportion to its concentration in the reaction solution. Manganese sulfate, or 
, is pale pink and absorbs light of a 500 nm wavelength in proportion to its concentration in the reaction solution. All other reactants and products are colorless and do not absorb visible light and thus cannot be monitored using the spectrophotometer.
Experiment 1:
The student constructed a standard curve, or a graph of the absorbance of solutions of varying concentrations of potassium permanganate, to quantify the relationship between concentration and absorbance. To prepare five sample of increasing concentration, he labeled five test tubes A, B, C, D, and E, weighed out 0.1, 0.2, 0.3, 0.4, and 0.5 grams of potassium permanganate into each, respectively, and added 1 milliliter (mL) of water to each test tube to dissolve. Then, he used the spectrophotometer to determine the absorbance at 550 nm of each sample. The data is graphed in Figure 1 below.
Figure 1
Experiment 2:
The student then studied potassium permanganate in the presence of oxalic acid, 
, to observe the reaction. Monitoring both the absorbances of potassium permanganate and manganese sulfate, he was able to determine the reaction rate using a special setting on the spectrophotometer. The reaction rate at various concentrations of reactants is shown below in Table 1.
A scientific relationship, known as Beer's Law, mathematically correlates absorbance to concentration via the following equation:
where 
is the absorbance, 
is the concentration of the sample, and 
is a constant specific for the chemical in the sample. According to Figure 1, what is the value of 
, in mL/g, for potassium permanganate?
A student wanted to study the kinetics, or rates of a chemical reaction based on the concentrations of its reactants and products, of the reaction shown below.
This reaction is easy to monitor using a spectrophotometer, which measures how much light of a particular wavelength is absorbed by a solution. The deep purple potassium permanganate, or
Experiment 1:
The student constructed a standard curve, or a graph of the absorbance of solutions of varying concentrations of potassium permanganate, to quantify the relationship between concentration and absorbance. To prepare five sample of increasing concentration, he labeled five test tubes A, B, C, D, and E, weighed out 0.1, 0.2, 0.3, 0.4, and 0.5 grams of potassium permanganate into each, respectively, and added 1 milliliter (mL) of water to each test tube to dissolve. Then, he used the spectrophotometer to determine the absorbance at 550 nm of each sample. The data is graphed in Figure 1 below.
Figure 1
Experiment 2:
The student then studied potassium permanganate in the presence of oxalic acid,
A scientific relationship, known as Beer's Law, mathematically correlates absorbance to concentration via the following equation:
where
You can solve for 
by plugging in corresponding values of 
and 
. For example, if we plugged in the concentration of 0.1 grams/mL for 
, and the corresponding absorbance it produces according to Figure 1 of 0.2 for 
, we obtain the following mathematical relationship:
By dividing, we can see that 
is 2.
Alternatively, you may view the equation 
like the equation of a line, like 
, where 
, 
, and 
, or the slope of the line. As the slope of the line in Figure 1 is clearly 2, we know the answer is 
.
You can solve for
By dividing, we can see that
Alternatively, you may view the equation
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A student wanted to study the kinetics, or rates of a chemical reaction based on the concentrations of its reactants and products, of the reaction shown below.
This reaction is easy to monitor using a spectrophotometer, which measures how much light of a particular wavelength is absorbed by a solution. The deep purple potassium permanganate, or , absorbs light of a 550 nm wavelength in proportion to its concentration in the reaction solution. Manganese sulfate, or , is pale pink and absorbs light of a 500 nm wavelength in proportion to its concentration in the reaction solution. All other reactants and products are colorless and do not absorb visible light and thus cannot be monitored using the spectrophotometer.
Experiment 1:
The student constructed a standard curve, or a graph of the absorbance of solutions of varying concentrations of potassium permanganate, to quantify the relationship between concentration and absorbance. To prepare five sample of increasing concentration, he labeled five test tubes A, B, C, D, and E, weighed out 0.1, 0.2, 0.3, 0.4, and 0.5 grams of potassium permanganate into each, respectively, and added 1 milliliter (mL) of water to each test tube to dissolve. Then, he used the spectrophotometer to determine the absorbance at 550 nm of each sample. The data is graphed in Figure 1 below.
Figure 1
Experiment 2:
The student then studied potassium permanganate in the presence of oxalic acid, 
, to observe the reaction. Monitoring both the absorbances of potassium permanganate and manganese sulfate, he was able to determine the reaction rate using a special setting on the spectrophotometer. The reaction rate at various concentrations of reactants is shown below in Table 1.
The "special setting" on the spectrophotometer underlined in the description of Experiment 2 likely involves what?
A student wanted to study the kinetics, or rates of a chemical reaction based on the concentrations of its reactants and products, of the reaction shown below.
This reaction is easy to monitor using a spectrophotometer, which measures how much light of a particular wavelength is absorbed by a solution. The deep purple potassium permanganate, or
Experiment 1:
The student constructed a standard curve, or a graph of the absorbance of solutions of varying concentrations of potassium permanganate, to quantify the relationship between concentration and absorbance. To prepare five sample of increasing concentration, he labeled five test tubes A, B, C, D, and E, weighed out 0.1, 0.2, 0.3, 0.4, and 0.5 grams of potassium permanganate into each, respectively, and added 1 milliliter (mL) of water to each test tube to dissolve. Then, he used the spectrophotometer to determine the absorbance at 550 nm of each sample. The data is graphed in Figure 1 below.
Figure 1
Experiment 2:
The student then studied potassium permanganate in the presence of oxalic acid,
The "special setting" on the spectrophotometer underlined in the description of Experiment 2 likely involves what?
"Measuring concentrations of potassium permanganate and manganese sulfate by observing their relative absorbances at 550 nm and 500 nm, respectively" is the correct answer. It is the only answer that contains chemicals that absorb visible light, and thus the only concentrations that may be monitored by the spectrophotometer, as stated in the introduction to the experiments.
"Measuring concentrations of potassium permanganate and manganese sulfate by observing their relative absorbances at 550 nm and 500 nm, respectively" is the correct answer. It is the only answer that contains chemicals that absorb visible light, and thus the only concentrations that may be monitored by the spectrophotometer, as stated in the introduction to the experiments.
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Clock reactions are chemical interactions that exhibit a physical change periodically over a given time interval. Many of these reactions involve iodine, the most famous being the Chlorine Dioxide-Iodine-Malonic Acid reaction. These reactions can be quite startling as flasks of colorless liquid periodically turn dark blue and then resolve back to their original colorless state. Even more striking, they seem to alternate between being colorless and blue several times. The term "clock reaction" is derived from the fact that the time at which these sudden changes occur can be predicted.
Beyond performing these reactions in a well stirred beaker, there are two other notable ways to conduct experiments with clock reactions that demonstrate interesting properties of these reactions. The first is in a continuous flow stirred tank reactor (CSTR). In a CSTR, the reactants are introduced at a continuous rate while the volume of liquid in the reactor is kept constant by siphoning off excess fluid. The result of this process is that one can maintain the ideal conditions in which the reaction may occur over time and restricts the buildup of excess product or reactant that would otherwise make the oscillations of the reactions decay. In a CSTR, clock reactions can be maintained switching predictably from colorless to blue, for example, for far longer than in a simple beaker.
The second way to conduct a clock reaction experiment is in a tank with no stirring at all. This allows the reactants to interact heterogeneously, or without being thoroughly mixed. When this occurs, we can get some parts of the tank that are one color and other parts that are another color. This means that we can observe two different stages of the reaction in one vessel. The patterns that this makes are called Turing patterns, named by the great computer scientist Alan Turing. Turing predicted that the heterogeneous mixing of chemicals called morphogens in complex organisms were responsible for biological pattern formation like spots on a leopard, stripes on a zebra, or patterns on a tropical fish. The existence of such patterns and chemicals has since been confirmed and clock reactions are often used to study these types of Turing patterns.
Given that different patterns happen when different concentrations of the reactants interact with each other, which of the following would NOT be a useful experimental variable in an experiment designed to explore the mechanism and dynamics of different patterns of chemicals in clock reactions?
Clock reactions are chemical interactions that exhibit a physical change periodically over a given time interval. Many of these reactions involve iodine, the most famous being the Chlorine Dioxide-Iodine-Malonic Acid reaction. These reactions can be quite startling as flasks of colorless liquid periodically turn dark blue and then resolve back to their original colorless state. Even more striking, they seem to alternate between being colorless and blue several times. The term "clock reaction" is derived from the fact that the time at which these sudden changes occur can be predicted.
Beyond performing these reactions in a well stirred beaker, there are two other notable ways to conduct experiments with clock reactions that demonstrate interesting properties of these reactions. The first is in a continuous flow stirred tank reactor (CSTR). In a CSTR, the reactants are introduced at a continuous rate while the volume of liquid in the reactor is kept constant by siphoning off excess fluid. The result of this process is that one can maintain the ideal conditions in which the reaction may occur over time and restricts the buildup of excess product or reactant that would otherwise make the oscillations of the reactions decay. In a CSTR, clock reactions can be maintained switching predictably from colorless to blue, for example, for far longer than in a simple beaker.
The second way to conduct a clock reaction experiment is in a tank with no stirring at all. This allows the reactants to interact heterogeneously, or without being thoroughly mixed. When this occurs, we can get some parts of the tank that are one color and other parts that are another color. This means that we can observe two different stages of the reaction in one vessel. The patterns that this makes are called Turing patterns, named by the great computer scientist Alan Turing. Turing predicted that the heterogeneous mixing of chemicals called morphogens in complex organisms were responsible for biological pattern formation like spots on a leopard, stripes on a zebra, or patterns on a tropical fish. The existence of such patterns and chemicals has since been confirmed and clock reactions are often used to study these types of Turing patterns.
Given that different patterns happen when different concentrations of the reactants interact with each other, which of the following would NOT be a useful experimental variable in an experiment designed to explore the mechanism and dynamics of different patterns of chemicals in clock reactions?
Since concentration is important to the pattern formation and the reactions happen over and over again in time, it seems that any answer that involves changing either the concentration of reactants directly or indirectly (via the volume of the reaction vessel into which the reactants are placed) is a valid experimental variable. The answer that would not be the most helpful is time because we know these reactions proceed over and over again in time.
Since concentration is important to the pattern formation and the reactions happen over and over again in time, it seems that any answer that involves changing either the concentration of reactants directly or indirectly (via the volume of the reaction vessel into which the reactants are placed) is a valid experimental variable. The answer that would not be the most helpful is time because we know these reactions proceed over and over again in time.
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The Millikin oil drop experiment is among the most important experiments in the history of science. It was used to determine one of the fundamental constants of the universe, the charge on the electron. For his work, Robert Millikin won the Nobel Prize in Physics in 1923.
Millikin used an experimental setup as follows in Figure 1. He opened a chamber of oil into an adjacent uniform electric field. The oil droplets sank into the electric field once the trap door opened, but were then immediately suspended by the forces of electricity present in the field.
Figure 1:
By determining how much force was needed to exactly counteract the gravity pulling the oil droplet down, Millikin was able to determine the force of electricity. This is depicted in Figure 2.
Using this information, he was able to calculate the exact charge on an electron. By changing some conditions, such as creating a vacuum in the apparatus, the experiment can be modified.
Figure 2:
When the drop is suspended perfectly, the total forces up equal the total forces down. Because Millikin knew the electric field in the apparatus, the force of air resistance, the mass of the drop, and the acceleration due to gravity, he was able to solve the following equation:
Table 1 summarizes the electric charge found on oil drops in suspension. Millikin correctly concluded that the calculated charges must all be multiples of the fundamental charge of the electron. A hypothetical oil drop contains some net charge due to lost electrons, and this net charge cannot be smaller than the charge on a single electron.
Table 1:
Trial # Electric Charge Calculated in Coulombs (C) Vacuum Used? 1 1.602176487 x 10-8 No 2 1.602176487 x 10-2 Yes 3 1.602176487 x 10-6 No 4 1.602176487 x 10-4 Yes
In Trial 1 and 3, the additional net force not present in Trial 2 and 4 is most probably acting:
The Millikin oil drop experiment is among the most important experiments in the history of science. It was used to determine one of the fundamental constants of the universe, the charge on the electron. For his work, Robert Millikin won the Nobel Prize in Physics in 1923.
Millikin used an experimental setup as follows in Figure 1. He opened a chamber of oil into an adjacent uniform electric field. The oil droplets sank into the electric field once the trap door opened, but were then immediately suspended by the forces of electricity present in the field.
Figure 1:
By determining how much force was needed to exactly counteract the gravity pulling the oil droplet down, Millikin was able to determine the force of electricity. This is depicted in Figure 2.
Using this information, he was able to calculate the exact charge on an electron. By changing some conditions, such as creating a vacuum in the apparatus, the experiment can be modified.
Figure 2:
When the drop is suspended perfectly, the total forces up equal the total forces down. Because Millikin knew the electric field in the apparatus, the force of air resistance, the mass of the drop, and the acceleration due to gravity, he was able to solve the following equation:
Table 1 summarizes the electric charge found on oil drops in suspension. Millikin correctly concluded that the calculated charges must all be multiples of the fundamental charge of the electron. A hypothetical oil drop contains some net charge due to lost electrons, and this net charge cannot be smaller than the charge on a single electron.
Table 1:
| Trial # | Electric Charge Calculated in Coulombs (C) | Vacuum Used? |
|---|---|---|
| 1 | 1.602176487 x 10-8 | No |
| 2 | 1.602176487 x 10-2 | Yes |
| 3 | 1.602176487 x 10-6 | No |
| 4 | 1.602176487 x 10-4 | Yes |
In Trial 1 and 3, the additional net force not present in Trial 2 and 4 is most probably acting:
The additional force in the absence of a vacuum is mainly air resistance, and the magnitude of the observed electric force suggests that the net force is acting parallel and opposite to gravity. Thus, it is in the same direction as the electric force.
The additional force in the absence of a vacuum is mainly air resistance, and the magnitude of the observed electric force suggests that the net force is acting parallel and opposite to gravity. Thus, it is in the same direction as the electric force.
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The Millikin oil drop experiment is among the most important experiments in the history of science. It was used to determine one of the fundamental constants of the universe, the charge on the electron. For his work, Robert Millikin won the Nobel Prize in Physics in 1923.
Millikin used an experimental setup as follows in Figure 1. He opened a chamber of oil into an adjacent uniform electric field. The oil droplets sank into the electric field once the trap door opened, but were then immediately suspended by the forces of electricity present in the field.
Figure 1:
By determining how much force was needed to exactly counteract the gravity pulling the oil droplet down, Millikin was able to determine the force of electricity. This is depicted in Figure 2.
Using this information, he was able to calculate the exact charge on an electron. By changing some conditions, such as creating a vacuum in the apparatus, the experiment can be modified.
Figure 2:
When the drop is suspended perfectly, the total forces up equal the total forces down. Because Millikin knew the electric field in the apparatus, the force of air resistance, the mass of the drop, and the acceleration due to gravity, he was able to solve the following equation:
Table 1 summarizes the electric charge found on oil drops in suspension. Millikin correctly concluded that the calculated charges must all be multiples of the fundamental charge of the electron. A hypothetical oil drop contains some net charge due to lost electrons, and this net charge cannot be smaller than the charge on a single electron.
Table 1:
Trial # Electric Charge Calculated in Coulombs (C) Vacuum Used? 1 1.602176487 x 10-8 No 2 1.602176487 x 10-2 Yes 3 1.602176487 x 10-6 No 4 1.602176487 x 10-4 Yes
The electric force experienced by oil drops will vary directly with the magnitude of charge on the drop. A scientist is measuring two different drops in two different experimental apparatuses, but each in perfect suspension and not moving. Drop 1 has a greater net charge than does drop 2. The magnitude of the electric force:
The Millikin oil drop experiment is among the most important experiments in the history of science. It was used to determine one of the fundamental constants of the universe, the charge on the electron. For his work, Robert Millikin won the Nobel Prize in Physics in 1923.
Millikin used an experimental setup as follows in Figure 1. He opened a chamber of oil into an adjacent uniform electric field. The oil droplets sank into the electric field once the trap door opened, but were then immediately suspended by the forces of electricity present in the field.
Figure 1:
By determining how much force was needed to exactly counteract the gravity pulling the oil droplet down, Millikin was able to determine the force of electricity. This is depicted in Figure 2.
Using this information, he was able to calculate the exact charge on an electron. By changing some conditions, such as creating a vacuum in the apparatus, the experiment can be modified.
Figure 2:
When the drop is suspended perfectly, the total forces up equal the total forces down. Because Millikin knew the electric field in the apparatus, the force of air resistance, the mass of the drop, and the acceleration due to gravity, he was able to solve the following equation:
Table 1 summarizes the electric charge found on oil drops in suspension. Millikin correctly concluded that the calculated charges must all be multiples of the fundamental charge of the electron. A hypothetical oil drop contains some net charge due to lost electrons, and this net charge cannot be smaller than the charge on a single electron.
Table 1:
| Trial # | Electric Charge Calculated in Coulombs (C) | Vacuum Used? |
|---|---|---|
| 1 | 1.602176487 x 10-8 | No |
| 2 | 1.602176487 x 10-2 | Yes |
| 3 | 1.602176487 x 10-6 | No |
| 4 | 1.602176487 x 10-4 | Yes |
The electric force experienced by oil drops will vary directly with the magnitude of charge on the drop. A scientist is measuring two different drops in two different experimental apparatuses, but each in perfect suspension and not moving. Drop 1 has a greater net charge than does drop 2. The magnitude of the electric force:
The electric force, in isolation, will be greater on drop 1 because it has a greater net charge to interact with the external electric field.
The electric force, in isolation, will be greater on drop 1 because it has a greater net charge to interact with the external electric field.
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