Chemical Reactions - GRE
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What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
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What is the pH of a 0.03M hydrochloric acid solution?
What is the pH of a 0.03M hydrochloric acid solution?
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
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What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where 
is concentration of hydrogen ions and 
is the concentration of hydroxide ions. Solve for 
:
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since 
and 
are in 1:1 ratio, the concentration of hydrogen ions will equal the concentration 
; therefore, 
. Note that this won’t be the case if the acid was weak. For a weak acid, the concentration of 
will be less than the concentration of acid, even if it was 1:1 ratio. This occurs because a weak acid does not dissociate completely.
We can now use the 
to solve for 
.
Therefore, concentration of hydroxide ions in this solution is 
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since
We can now use the
Therefore, concentration of hydroxide ions in this solution is
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Which of the following substances is considered a Lewis acid?
Which of the following substances is considered a Lewis acid?
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question. 
, or borane, is considered a Lewis acid because it accepts an electron pair. Boron has four orbitals in its outermost shell. If we look at Boron in borane, we will notice that three orbitals are occupied by the electrons in the three single bonds (bound to hydrogen) whereas the last orbital is empty and is free to accept electrons. Since it accepts electrons, borane is considered a lewis acid. 
, or ammonia, is a lewis base. If we look at the nitrogen atom in ammonia, we will notice that all of its orbitals are occupied (three orbitals are occupied with the three bonds to hydrogen atoms and the last orbital is occupied with a lone electron pair). Since it has extra electrons in the last orbital, ammonia can donate electrons and is considered a lewis base.
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question.
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Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the 
of solution A is higher whereas the 
of acid in solution B is lower. What can be concluded about these results?
Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the
The question states that the 
of solution A is higher. The definition of 
is:
If we rearrange and solve for concentration of hydroxide ions, we get
This means that 
decreases as 
increases. The relationship between hydroxide ion and hydrogen ion is as follows
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher 
, its hydroxide ion concentration is lower than solution B. This means that solution A has higher hydrogen ion concentration and, therefore, is more acidic than solution B.
The question also states that the 
of solution B is lower. Recall that as 
of an acid decreases it becomes more acidic. Based on this, we conclude that solution B is more acidic. The two results given in this question conflict each other; therefore, these results seem invalid.
The question states that the
If we rearrange and solve for concentration of hydroxide ions, we get
This means that
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher
The question also states that the
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The pH of a solution
when the acid dissociation constant
.
The pH of a solution when the acid dissociation constant .
Acid dissociation constant, or 
, for a prototypical acid-base reaction is defined as
where 
is an acid and 
is its conjugate base. Based on this equation, we can determine that 
and 
are directly proportional to one another; therefore, increasing 
will increase 
and vice versa.
Recall the definition of 
Solving for 
gives us
This means that increasing pH will decrease 
and vice versa (has the opposite effect on each other); therefore, 
and 
also have an opposite effect on each other.
Acid dissociation constant, or
where
Recall the definition of
Solving for
This means that increasing pH will decrease
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A buffer can be created by adding equal amounts of weak acid and its conjugate base. What additional information is needed to determine the pKa of a buffer made in this manner?
A buffer can be created by adding equal amounts of weak acid and its conjugate base. What additional information is needed to determine the pKa of a buffer made in this manner?
The buffer is made by using weak acid and its conjugate base. The relationship between the concentration of the components (acid and conjugate base), pKa, and pH can be determined by using the Henderson-Hasselbalch equation.
where 
is weak acid and 
is the conjugate base. We know that equal amounts of 
and 
are added; therefore, 
for buffer solutions made in this manner. To calculate the pKa of the solution we need the pH.
The buffer is made by using weak acid and its conjugate base. The relationship between the concentration of the components (acid and conjugate base), pKa, and pH can be determined by using the Henderson-Hasselbalch equation.
where
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A researcher adds 
acid to 
. The concentration of hydrogen ions is
as the concentration of hydroxide ions.
A researcher adds
Hydrochloric acid (
) and sodium hydroxide (
) are both strong reagents. Adding equal amounts of strong acid to a strong base neutralizes the solution and gives the solution a neutral pH of 7. This means that the concentration of hydrogen ions and hydroxide ions are equal to each other. If pH was greater than 7 (basic pH), then the hydroxide ion concentration would be higher and if pH was less than 7 (acidic pH) then hydrogen ion concentration would be higher.
Hydrochloric acid (
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Solution A contains a weak acid and a weak base whereas solution B contains a weak acid and a strong base. What can you conclude about these two solutions?
I. Solution B will have a higher 
II. Solution B will have a higher pOH
III. Solution A will have a lower concentration of hydroxide ions
Solution A contains a weak acid and a weak base whereas solution B contains a weak acid and a strong base. What can you conclude about these two solutions?
I. Solution B will have a higher
II. Solution B will have a higher pOH
III. Solution A will have a lower concentration of hydroxide ions
Solution A has two weak reagents whereas solution B contains a strong base. This means that solution B will be more basic, will have a higher concentration of hydroxide ions, and a higher pH. 
is a constant and is not altered by the relative reagents (it is always equal to 
). Recall that pOH is defined as
This equation suggests that pOH decreases as the hydroxide ion concentration increases. Since it has the higher hydroxide ion concentration, solution B will have a lower pOH.
Solution A has two weak reagents whereas solution B contains a strong base. This means that solution B will be more basic, will have a higher concentration of hydroxide ions, and a higher pH.
This equation suggests that pOH decreases as the hydroxide ion concentration increases. Since it has the higher hydroxide ion concentration, solution B will have a lower pOH.
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What is the pH of a solution composed of 
acetic acid and 
acetate?
for acetic acid is 
What is the pH of a solution composed of
Since this problem involves both the acid and the conjugate base of the acid, we can use the Henderson-Hasselbach equation in order to determine the pH of the solution:
Since this problem involves both the acid and the conjugate base of the acid, we can use the Henderson-Hasselbach equation in order to determine the pH of the solution:
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If a 
solution of hydrofluoric acid is created, what fluoride ion concentration must be present in order to make the new pH of the solution equal to 
?
for hydrofluoric acid is 
If a
In order to determine what concentration of fluoride is needed, we can use the Henderson-Hasselbach equation:
In order to determine what concentration of fluoride is needed, we can use the Henderson-Hasselbach equation:
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Which of the following is not a redox reaction?
Which of the following is not a redox reaction?
All of the given choices represent oxidation-reduction reactions that are important in cellular metabolism. Oxidation-reduction reactions involve the changing of oxidation states (commonly through the transfer of electrons). In the first reaction NAD+ is reduced. The second reaction shows the polymerization of two molecules of glucose via a condensation (dehydration synthesis) reaction. In the third reaction glucose is oxidized.
NADH and are important electron carriers that bring electrons to the electron transport chain and are formed during glycolysis and the Krebs cycle via reduction. The final choice represents the overall oxidation-reduction reaction that occurs for one molecule of glucose.
All of the given choices represent oxidation-reduction reactions that are important in cellular metabolism. Oxidation-reduction reactions involve the changing of oxidation states (commonly through the transfer of electrons). In the first reaction NAD+ is reduced. The second reaction shows the polymerization of two molecules of glucose via a condensation (dehydration synthesis) reaction. In the third reaction glucose is oxidized.
NADH and are important electron carriers that bring electrons to the electron transport chain and are formed during glycolysis and the Krebs cycle via reduction. The final choice represents the overall oxidation-reduction reaction that occurs for one molecule of glucose.
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Consider the following reaction:
Which atom is oxidized in the reaction?
Consider the following reaction:
Which atom is oxidized in the reaction?
Oxidation is the process of losing electrons, or acquiring a more positive charge. We can determine which atom has lost electrons by comparing the oxidation number of the atom as a reactant and as a product. Aluminum is in elemental form as a reactant, so it has an oxidation number of 0. As a product, it is bonded with oxygen, giving each aluminum an oxidation number of +3. Since it has a more positive charge, the aluminum has been oxidized.
Oxidation is the process of losing electrons, or acquiring a more positive charge. We can determine which atom has lost electrons by comparing the oxidation number of the atom as a reactant and as a product. Aluminum is in elemental form as a reactant, so it has an oxidation number of 0. As a product, it is bonded with oxygen, giving each aluminum an oxidation number of +3. Since it has a more positive charge, the aluminum has been oxidized.
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Which mnemonic would be most useful for remembering what happens during an oxidation-reduction reaction?
Which mnemonic would be most useful for remembering what happens during an oxidation-reduction reaction?
LEO says GER is a mnemonic for Loss of Electrons is Oxidation, Gain of Electrons is Reduction. An oxidation-reduction reaction is a chemical interaction in which one substance is oxidized and loses electrons, and thus is increased in positive valance, while another substance gains an equal number of electrons and is reduced, thus decreasing in positive valance. This is called a redox system or reaction. Along with LEO says GER, another popular mnemonic for this system is "OIL RIG," which stands for Oxidation is Loss, Reduction is Gain (in reference to electrons).
BARF is a mnemonic for Break (a bond) Absorb (energy), Release (energy) Form (a bond). This is used to remember whether energy is required or released when chemical bonds are broken and formed. OCEAN describes the big five personality traits: openness, conscientiousness, extraversion, agreeableness, and neuroticism. PASS stands for pull, aim, squeeze, and sweep—how to use a fire extinguisher. ROME is a mnemonic for Respiratory Opposite, Metabolic Equal. The values for the respiratory form of acid-base balance are opposite; if pH is high, carbon dioxide will be low and vice versa. For the metabolic form, the values are equal. If pH is high, carbonic acid will be high. If pH is low, carbonic acid will be low.
LEO says GER is a mnemonic for Loss of Electrons is Oxidation, Gain of Electrons is Reduction. An oxidation-reduction reaction is a chemical interaction in which one substance is oxidized and loses electrons, and thus is increased in positive valance, while another substance gains an equal number of electrons and is reduced, thus decreasing in positive valance. This is called a redox system or reaction. Along with LEO says GER, another popular mnemonic for this system is "OIL RIG," which stands for Oxidation is Loss, Reduction is Gain (in reference to electrons).
BARF is a mnemonic for Break (a bond) Absorb (energy), Release (energy) Form (a bond). This is used to remember whether energy is required or released when chemical bonds are broken and formed. OCEAN describes the big five personality traits: openness, conscientiousness, extraversion, agreeableness, and neuroticism. PASS stands for pull, aim, squeeze, and sweep—how to use a fire extinguisher. ROME is a mnemonic for Respiratory Opposite, Metabolic Equal. The values for the respiratory form of acid-base balance are opposite; if pH is high, carbon dioxide will be low and vice versa. For the metabolic form, the values are equal. If pH is high, carbonic acid will be high. If pH is low, carbonic acid will be low.
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Reduction of a compound results in a
of electrons, thus rendering the compound's charge to be more
.
Reduction of a compound results in a of electrons, thus rendering the compound's charge to be more .
The process of reduction causes a gain of electrons. Because electrons are negatively charged, any compound that becomes reduced will be more negative than it was prior to the reaction.
The process of reduction causes a gain of electrons. Because electrons are negatively charged, any compound that becomes reduced will be more negative than it was prior to the reaction.
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What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
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What is the pH of a 0.03M hydrochloric acid solution?
What is the pH of a 0.03M hydrochloric acid solution?
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
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What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where is concentration of hydrogen ions and is the concentration of hydroxide ions. Solve for :
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since and are in 1:1 ratio, the concentration of hydrogen ions will equal the concentration ; therefore, . Note that this won’t be the case if the acid was weak. For a weak acid, the concentration of will be less than the concentration of acid, even if it was 1:1 ratio. This occurs because a weak acid does not dissociate completely.
We can now use the to solve for .
Therefore, concentration of hydroxide ions in this solution is
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since
We can now use the
Therefore, concentration of hydroxide ions in this solution is
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Which of the following substances is considered a Lewis acid?
Which of the following substances is considered a Lewis acid?
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question. , or borane, is considered a Lewis acid because it accepts an electron pair. Boron has four orbitals in its outermost shell. If we look at Boron in borane, we will notice that three orbitals are occupied by the electrons in the three single bonds (bound to hydrogen) whereas the last orbital is empty and is free to accept electrons. Since it accepts electrons, borane is considered a lewis acid. , or ammonia, is a lewis base. If we look at the nitrogen atom in ammonia, we will notice that all of its orbitals are occupied (three orbitals are occupied with the three bonds to hydrogen atoms and the last orbital is occupied with a lone electron pair). Since it has extra electrons in the last orbital, ammonia can donate electrons and is considered a lewis base.
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question.
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Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the of solution A is higher whereas the of acid in solution B is lower. What can be concluded about these results?
Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the
The question states that the of solution A is higher. The definition of is:
If we rearrange and solve for concentration of hydroxide ions, we get
This means that decreases as increases. The relationship between hydroxide ion and hydrogen ion is as follows
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher , its hydroxide ion concentration is lower than solution B. This means that solution A has higher hydrogen ion concentration and, therefore, is more acidic than solution B.
The question also states that the of solution B is lower. Recall that as of an acid decreases it becomes more acidic. Based on this, we conclude that solution B is more acidic. The two results given in this question conflict each other; therefore, these results seem invalid.
The question states that the
If we rearrange and solve for concentration of hydroxide ions, we get
This means that
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher
The question also states that the
Compare your answer with the correct one above