ACT Science : How to find conflicting viewpoints in chemistry

Study concepts, example questions & explanations for ACT Science

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Example Questions

Example Question #11 : How To Find Conflicting Viewpoints In Chemistry

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 a flask of water, which has been boiled to release any dissolved oxygen. The flask is attached to a vacuum pump which removes the air inside it. Then the flask is sealed. Assuming that the explanation of Scientist 1 is correct, which of the following results will be observed?

Possible Answers:

No hydrated iron oxide will form on the surface of the iron.

Oxygen will build up inside the flask.

Hydroxide ions will be produced in the solution.

Iron hydroxide will be produced, but will not be converted to iron oxide.

Hydrated iron oxide will form on the surface of the iron.

Correct answer:

No hydrated iron oxide will form on the surface of the iron.

Explanation:

Scientist 1 states that for rust (hydrated iron oxide) to form, oxygen must dissolve in water and to react with water to form hydroxide ions. However, in this question, the vacuum pump removes all the air (including oxygen) in the flask. So, no oxygen would be able to react to produce hydroxide ions—meaning that no iron hydroxide will be produced, and no rust will be produced either.

Example Question #12 : How To Find Conflicting Viewpoints In Chemistry

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 a test tube filled with water. Then, a layer of oil is poured over the water. After an extended period of time, no rust is observed to have formed on the iron nail. Scientist 1 would most likely explain this result by saying that:

Possible Answers:

The layer of oil prevented atmospheric oxygen from dissolving in the water, increasing the production of OH- ions.

The layer of oil prevented atmospheric oxygen from dissolving in the water, reducing the production of OH- ions.

The layer of oil allowed atmospheric oxygen to dissolve in the water, reducing the production of OH- ions.

The layer of oil allowed atmospheric oxygen to dissolve in the water, increasing the production of OH- ions.

Correct answer:

The layer of oil prevented atmospheric oxygen from dissolving in the water, reducing the production of OH- ions.

Explanation:

Scientist 1 states that for rust to form, oxygen must dissolve in water and react with water to form hydroxide (OH-) ions. In this case, no rust is observed to form. This suggests that the layer of oil blocked the diffusion of oxygen into the water, preventing the production of OH- ions—and thus, of rust.

Example Question #13 : How To Find Conflicting Viewpoints In Chemistry

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 1's hypothesis?

Possible Answers:

When table salt is dissolved in water, the water is better able to conduct an electrical current.

When the concentration of dissolved oxygen in a solution is increased, rust forms more quickly on iron in the solution. 

When the concentration of hydroxide ions in a solution is increased, rust forms less quickly on iron in the solution.

In the absence of liquid water, iron does not rust.

When table salt is dissolved in water, the rate at which Fe2+ ions are produced increases.

Correct answer:

When the concentration of hydroxide ions in a solution is increased, rust forms less quickly on iron in the solution.

Explanation:

According to Scientist 1, the production of hydroxide ions is needed in order for rust to form. Scientist 1 states that hydroxide ions combine with soluble iron ions to form iron hydroxide, which then changes into hydrated iron oxide, or rust. Since hydroxide ions are one of the reactants used to produce rust, increasing the concentration of hydroxide ions in a solution should speed up the formation of rust. However, if increasing the hydroxide concentration actually slows down the formation of rust, this would suggest that Scientist 1's explanation is incorrect.

Example Question #11 : How To Find Conflicting Viewpoints In Chemistry

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?

Possible Answers:

When two iron nails are immersed in identical solutions of acid and water, they rust at different rates.

When an iron nail is immersed in water in an open container, rust forms on the nail even in the absence of added acid.

When immersed in a solution of water and acid, a galvanized piece of iron does not rust.

When oxygen is prevented from dissolving into a solution which contains a piece of iron, the iron does not rust.

When a rusted piece of iron is immersed in lemon juice (citric acid), it becomes shiny again.

Correct answer:

When a rusted piece of iron is immersed in lemon juice (citric acid), it becomes shiny again.

Explanation:

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.

Example Question #15 : How To Find Conflicting Viewpoints In Chemistry

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 __________.

Possible Answers:

increase, because the concentration of H+ ions in the solution will increase

decrease, because the solution will become less acidic

increase, because rust requires hydroxide ions to form

increase, because more Fe2+ ions will be produced

decrease, because the solution will become more acidic

Correct answer:

decrease, because the solution will become less acidic

Explanation:

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.

Example Question #16 : How To Find Conflicting Viewpoints In Chemistry

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 __________.

Possible Answers:

the iron nail contained impurities, with reacted with water to form OH- ions

the iron nail contained impurities, which reacted with water to form carbonic acid

oxygen from the air dissolved in the water and reacted to form OH- ions

the iron nail contained impurities, which reacted with water to form iron oxide

carbon dioxide from the air dissolved in the water and reacted to form carbonic acid

Correct answer:

carbon dioxide from the air dissolved in the water and reacted to form carbonic acid

Explanation:

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.

Example Question #12 : How To Find Conflicting Viewpoints In Chemistry

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 __________.

Possible Answers:

sodium hydroxide neutralized the acid in the water, slowing the formation of iron hydroxide

sodium hydroxide increased the concentration of hydroxide irons in the water, facilitating the formation of iron hydroxide

sodium hydroxide neutralized the acid in the water, facilitating the formation of iron hydroxide

sodium hydroxide increased the concentration of hydroxide ions in the water, slowing the formation of iron hydroxide

sodium hydroxide increased the concentration of oxygen in the water, facilitating the formation of iron hydroxide

Correct answer:

sodium hydroxide increased the concentration of hydroxide irons in the water, facilitating the formation of iron hydroxide

Explanation:

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.

Example Question #18 : How To Find Conflicting Viewpoints In Chemistry

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?

Possible Answers:

Placing powdered iron in water at 30°C

Placing powdered iron in water at 5°C

Placing a strip of iron in water at 30°C

Placing powdered iron in water at 30°C and adding table salt

Placing a strip of iron in water at 5°C

Correct answer:

Placing a strip of iron in water at 5°C

Explanation:

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.

Example Question #13 : How To Find Conflicting Viewpoints In Chemistry

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?

Possible Answers:

An iron pot is coated with zinc, then immersed in water in an unsealed container.

Rust will not form in any of the situations listed.

An iron pot is placed in a sealed chamber containing carbon dioxide gas.

An iron pot is immersed in water in an unsealed container.

An iron pot is placed in a sealed chamber containing oxygen gas.

Correct answer:

An iron pot is immersed in water in an unsealed container.

Explanation:

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.

Example Question #20 : How To Find Conflicting Viewpoints In Chemistry

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?

Possible Answers:

Iron oxide will be produced because the solution is basic.

Iron oxide will not be produced because the solution is basic.

Iron oxide will not be produced because the solution is acidic.

Iron oxide will be produced because the solution is acidic.

Correct answer:

Iron oxide will not be produced because the solution is basic.

Explanation:

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.

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