Acid-Base Equilibrium - MCAT Physical
Card 0 of 91
Compound Base strength, K b 1 1012 2 105 3 101 4 10-8
Students in a chemistry class are given one of four unknown samples in a laboratory. A student is told that his compound is the strongest acid of the four compounds. Based on the information in the above table, which compound was the student given?
| Compound | Base strength, K b |
|---|---|
| 1 | 1012 |
| 2 | 105 |
| 3 | 101 |
| 4 | 10-8 |
Students in a chemistry class are given one of four unknown samples in a laboratory. A student is told that his compound is the strongest acid of the four compounds. Based on the information in the above table, which compound was the student given?
The strongest acid of the group will also have the smallest Kb value. As the weakest base (smallest Kb), compound 4 will only partially dissociate in solution because it has a fairly strong conjugate acid. Were this question asking which base was the strongest, compound 1 would be the answer, due to its large Kb value.
The strongest acid of the group will also have the smallest Kb value. As the weakest base (smallest Kb), compound 4 will only partially dissociate in solution because it has a fairly strong conjugate acid. Were this question asking which base was the strongest, compound 1 would be the answer, due to its large Kb value.
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What is the pKa of acetic acid? (Ka = 1.8 * 10–5)
What is the pKa of acetic acid? (Ka = 1.8 * 10–5)
We know that pKa is equal to –log(Ka). Thus, pKa of acetic acid is –log(1.8 * 10–5). This is not an easy problem to solve in your head, but there is a trick.
We know that 1 * 10–4 > 1.8 * 10–5 > 1 * 10–5, and we know that –log(1 * 10–4) = 4 and –log(1 * 10–5) = 5. Now we can conclude that our pKa is somewhere between 4 and 5.
Two answer choices fall in this range: 4.2 and 4.7.
1.8 * 10–5 is closer to 1 * 10–5 than it is to 1 * 10–4, so we can pick the answer closer to 5 than to 4 : 4.7.
We know that pKa is equal to –log(Ka). Thus, pKa of acetic acid is –log(1.8 * 10–5). This is not an easy problem to solve in your head, but there is a trick.
We know that 1 * 10–4 > 1.8 * 10–5 > 1 * 10–5, and we know that –log(1 * 10–4) = 4 and –log(1 * 10–5) = 5. Now we can conclude that our pKa is somewhere between 4 and 5.
Two answer choices fall in this range: 4.2 and 4.7.
1.8 * 10–5 is closer to 1 * 10–5 than it is to 1 * 10–4, so we can pick the answer closer to 5 than to 4 : 4.7.
Compare your answer with the correct one above
As the value of Ka increases, __________
As the value of Ka increases, __________
Ka represents the equilibrium constant for the acid dissociation in water, HA → H+ + A–, so it is a measure of the products divided by the reactants. As this value increases, the reaction favors the products (the ions) more, meaning that the acid dissociates more. The definition of a strong acid is one that fully dissociates in water, so as Ka increases the strength of the acid increases, and the strength of the conjugate base decreases. pKa is defined as the –log(Ka), so as Ka increases pKa decreases. All of these answer choices are correct.
Ka represents the equilibrium constant for the acid dissociation in water, HA → H+ + A–, so it is a measure of the products divided by the reactants. As this value increases, the reaction favors the products (the ions) more, meaning that the acid dissociates more. The definition of a strong acid is one that fully dissociates in water, so as Ka increases the strength of the acid increases, and the strength of the conjugate base decreases. pKa is defined as the –log(Ka), so as Ka increases pKa decreases. All of these answer choices are correct.
Compare your answer with the correct one above
Diffusion can be defined as the net transfer of molecules down a gradient of differing concentrations. This is a passive and spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic unit of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveoli separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One such equation used in determining gas exchange is Fick's law, given by:
ΔV = (Area/Thickness) · Dgas · (P1 – P2)
Where ΔV is flow rate and area and thickness refer to the permeable membrane through which the gas passes, in this case, the wall of the avlveoli. P1 and P2 refer to the partial pressures upstream and downstream, respectively. Further, Dgas, the diffusion constant of the gas, is defined as:
Dgas = Solubility / (Molecular Weight)^(1/2)
Which following pair gives the correct equation, and change in pH, when carbon dioxide diffuses into blood?
Diffusion can be defined as the net transfer of molecules down a gradient of differing concentrations. This is a passive and spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic unit of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveoli separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One such equation used in determining gas exchange is Fick's law, given by:
ΔV = (Area/Thickness) · Dgas · (P1 – P2)
Where ΔV is flow rate and area and thickness refer to the permeable membrane through which the gas passes, in this case, the wall of the avlveoli. P1 and P2 refer to the partial pressures upstream and downstream, respectively. Further, Dgas, the diffusion constant of the gas, is defined as:
Dgas = Solubility / (Molecular Weight)^(1/2)
Which following pair gives the correct equation, and change in pH, when carbon dioxide diffuses into blood?
This is essentially a two-part question. The first asks you to generate the production of carbonic acid; and the second, requires you to infer that an acid will lower blood pH. Only one answer choice is both balanced correctly and gives an accurate change in pH. Although this knowledge is not required for the MCAT, your body constantly monitors blood pH to determine if concentrations of CO2 are too high, or alternatively, if O2 concentrations are too low.
This is essentially a two-part question. The first asks you to generate the production of carbonic acid; and the second, requires you to infer that an acid will lower blood pH. Only one answer choice is both balanced correctly and gives an accurate change in pH. Although this knowledge is not required for the MCAT, your body constantly monitors blood pH to determine if concentrations of CO2 are too high, or alternatively, if O2 concentrations are too low.
Compare your answer with the correct one above
Given the above values of Ka, place the acids in order from strongest to weakest.
Given the above values of Ka, place the acids in order from strongest to weakest.
The acid dissociation constant, Ka, describes how strongly an acid tends to break apart into hydrogen ions (H+) and its conjugate base (A-). The higher the dissociation constant, the stronger the acid. HF has the largest Ka of these acids, making it the strongest, and H2CO3 has the smallest Ka, making it the weakest.
The acid dissociation constant, Ka, describes how strongly an acid tends to break apart into hydrogen ions (H+) and its conjugate base (A-). The higher the dissociation constant, the stronger the acid. HF has the largest Ka of these acids, making it the strongest, and H2CO3 has the smallest Ka, making it the weakest.
Compare your answer with the correct one above
What is the pH of a solution which has a hydroxide ion concentration of 5 * 10-4M?
What is the pH of a solution which has a hydroxide ion concentration of 5 * 10-4M?
First convert concentration of OH- into concentration of H+. Remember that Kw is 1*10-14.
Then, convert concentration of H+ into pH.
Alternatively, you can use the hydroxide concentration to solve for pOH and convert to pH.
First convert concentration of OH- into concentration of H+. Remember that Kw is 1*10-14.
Then, convert concentration of H+ into pH.
Alternatively, you can use the hydroxide concentration to solve for pOH and convert to pH.
Compare your answer with the correct one above
HCN dissociates based on the following reaction.
The Ka for hydrogen cyanide is 
.
What is the Kb for CN-?
HCN dissociates based on the following reaction.
The Ka for hydrogen cyanide is
What is the Kb for CN-?
Remember that the Ka for the acid and the Kb for the conjugate base, when multiplied will equal the autoionization of water constant (Kw).
Remember that the Ka for the acid and the Kb for the conjugate base, when multiplied will equal the autoionization of water constant (Kw).
Compare your answer with the correct one above
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
In aqueous conditions the equilibrium constant for a Brønsted-Lowry base, 
, can be expressed as which of the following?
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
In aqueous conditions the equilibrium constant for a Brønsted-Lowry base,
The base reaction will essentially be the reverse of the acid reaction. In the question, the aqueous conditions mean that the base, 
, reacts with water to give the following reaction:
Following normal equilibrium convention, we omit water from the equation because it is a pure liquid.
The base reaction will essentially be the reverse of the acid reaction. In the question, the aqueous conditions mean that the base,
Following normal equilibrium convention, we omit water from the equation because it is a pure liquid.
Compare your answer with the correct one above
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
Which of the following expressions most closely approximates the equilibrium constant of pure water?
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
Which of the following expressions most closely approximates the equilibrium constant of pure water?
The autionization of water proceeds as follows:
The equilibrium constant is calculated by the following formula.
The equilibrium expression is 
, with the pure water reactant excluded. Pure solids and liquids are not included in the equilibrium calculation.
The autionization of water proceeds as follows:
The equilibrium constant is calculated by the following formula.
The equilibrium expression is
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What is the hydroxide concentration in an aqueous solution with a pH of 2?
What is the hydroxide concentration in an aqueous solution with a pH of 2?
The hydroxide concentration can be determined by considering the autoionization of water in a solution. At 
, water has the equilibrium constant of 
. This value is based on the autoionization of water.
Since the reaction is in terms of proton and hydroxide ion concentrations, we can set the expression equal to this value in order to determine the concentration of hydroxide ions at the given pH. We start by determining the concentration of protons in the solution by using the following equation:
Now, we can solve for the hydroxide concentration.
This problem can also be solved by calculating the pOH of the solution and using this value to find the hydroxide ion concentration.
The hydroxide concentration can be determined by considering the autoionization of water in a solution. At
Since the reaction is in terms of proton and hydroxide ion concentrations, we can set the expression equal to this value in order to determine the concentration of hydroxide ions at the given pH. We start by determining the concentration of protons in the solution by using the following equation:
Now, we can solve for the hydroxide concentration.
This problem can also be solved by calculating the pOH of the solution and using this value to find the hydroxide ion concentration.
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Based on the above information, it is expected that __________.
Based on the above information, it is expected that __________.
Since the product of the cation and anion is 
, the only true statement is that the concentration of the cation 
is the square root of this number:
Since the product of the cation and anion is
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A solution of hydrofluoric acid has a concentration of 
The 
for 
is 
.
What is the pH of the solution?
A solution of hydrofluoric acid has a concentration of
The
What is the pH of the solution?
Since hydrofluoric acid is a weak acid, an ICE table needs to be set up in order to determine the hydronium ion concentration. Since both fluoride ion and hydronium ion concentrations will increase by 
, while the acid concentration will decrease by 
, the equilibrium expression comes out to be:
Note that the 
in the denominator will have a negligible effect and can be ignored.
Since 
is equal to the hydronium ion concentration, we can calculate the pH by taking the negative log of the concentration:
Since hydrofluoric acid is a weak acid, an ICE table needs to be set up in order to determine the hydronium ion concentration. Since both fluoride ion and hydronium ion concentrations will increase by
Note that the
Since
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A solution of hydrofluoric acid has a concentration of .
The 
for 
is 
.
If sodium hydroxide is slowly added to the acid solution, what will the pH be at the equivalence point?
Assume the concentration of the acid is not changed with the addition.
A solution of hydrofluoric acid has a concentration of
The
If sodium hydroxide is slowly added to the acid solution, what will the pH be at the equivalence point?
Assume the concentration of the acid is not changed with the addition.
At the equivalence point, there are equimolar amounts of acid and base. This means that all weak acid has been neutralized, and only the conjugate base remains. Since the conjugate base of a weak acid will affect the pH, we need to use an ICE table in order to find the pH. First, we start by finding the base dissociation constant of the conjugate base, using the equation:
The balanced equation for the conjugate base dissociation is:
As the hydroxide ion and acid concentrations increase by 
, the fluoride ion concentration will decrease by 
. This makes the equilibrium expression:
Since this is the hydroxide concentration, we can find the pH by taking the negative log of this value, then subtracting from 14:
At the equivalence point, there are equimolar amounts of acid and base. This means that all weak acid has been neutralized, and only the conjugate base remains. Since the conjugate base of a weak acid will affect the pH, we need to use an ICE table in order to find the pH. First, we start by finding the base dissociation constant of the conjugate base, using the equation:
The balanced equation for the conjugate base dissociation is:
As the hydroxide ion and acid concentrations increase by
Since this is the hydroxide concentration, we can find the pH by taking the negative log of this value, then subtracting from 14:
Compare your answer with the correct one above
As the value of Ka increases, __________
As the value of Ka increases, __________
Ka represents the equilibrium constant for the acid dissociation in water, HA → H+ + A–, so it is a measure of the products divided by the reactants. As this value increases, the reaction favors the products (the ions) more, meaning that the acid dissociates more. The definition of a strong acid is one that fully dissociates in water, so as Ka increases the strength of the acid increases, and the strength of the conjugate base decreases. pKa is defined as the –log(Ka), so as Ka increases pKa decreases. All of these answer choices are correct.
Ka represents the equilibrium constant for the acid dissociation in water, HA → H+ + A–, so it is a measure of the products divided by the reactants. As this value increases, the reaction favors the products (the ions) more, meaning that the acid dissociates more. The definition of a strong acid is one that fully dissociates in water, so as Ka increases the strength of the acid increases, and the strength of the conjugate base decreases. pKa is defined as the –log(Ka), so as Ka increases pKa decreases. All of these answer choices are correct.
Compare your answer with the correct one above
What is the pKa of acetic acid? (Ka = 1.8 * 10–5)
What is the pKa of acetic acid? (Ka = 1.8 * 10–5)
We know that pKa is equal to –log(Ka). Thus, pKa of acetic acid is –log(1.8 * 10–5). This is not an easy problem to solve in your head, but there is a trick.
We know that 1 * 10–4 > 1.8 * 10–5 > 1 * 10–5, and we know that –log(1 * 10–4) = 4 and –log(1 * 10–5) = 5. Now we can conclude that our pKa is somewhere between 4 and 5.
Two answer choices fall in this range: 4.2 and 4.7.
1.8 * 10–5 is closer to 1 * 10–5 than it is to 1 * 10–4, so we can pick the answer closer to 5 than to 4 : 4.7.
We know that pKa is equal to –log(Ka). Thus, pKa of acetic acid is –log(1.8 * 10–5). This is not an easy problem to solve in your head, but there is a trick.
We know that 1 * 10–4 > 1.8 * 10–5 > 1 * 10–5, and we know that –log(1 * 10–4) = 4 and –log(1 * 10–5) = 5. Now we can conclude that our pKa is somewhere between 4 and 5.
Two answer choices fall in this range: 4.2 and 4.7.
1.8 * 10–5 is closer to 1 * 10–5 than it is to 1 * 10–4, so we can pick the answer closer to 5 than to 4 : 4.7.
Compare your answer with the correct one above
Diffusion can be defined as the net transfer of molecules down a gradient of differing concentrations. This is a passive and spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic unit of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveoli separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One such equation used in determining gas exchange is Fick's law, given by:
ΔV = (Area/Thickness) · Dgas · (P1 – P2)
Where ΔV is flow rate and area and thickness refer to the permeable membrane through which the gas passes, in this case, the wall of the avlveoli. P1 and P2 refer to the partial pressures upstream and downstream, respectively. Further, Dgas, the diffusion constant of the gas, is defined as:
Dgas = Solubility / (Molecular Weight)^(1/2)
Which following pair gives the correct equation, and change in pH, when carbon dioxide diffuses into blood?
Diffusion can be defined as the net transfer of molecules down a gradient of differing concentrations. This is a passive and spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic unit of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveoli separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One such equation used in determining gas exchange is Fick's law, given by:
ΔV = (Area/Thickness) · Dgas · (P1 – P2)
Where ΔV is flow rate and area and thickness refer to the permeable membrane through which the gas passes, in this case, the wall of the avlveoli. P1 and P2 refer to the partial pressures upstream and downstream, respectively. Further, Dgas, the diffusion constant of the gas, is defined as:
Dgas = Solubility / (Molecular Weight)^(1/2)
Which following pair gives the correct equation, and change in pH, when carbon dioxide diffuses into blood?
This is essentially a two-part question. The first asks you to generate the production of carbonic acid; and the second, requires you to infer that an acid will lower blood pH. Only one answer choice is both balanced correctly and gives an accurate change in pH. Although this knowledge is not required for the MCAT, your body constantly monitors blood pH to determine if concentrations of CO2 are too high, or alternatively, if O2 concentrations are too low.
This is essentially a two-part question. The first asks you to generate the production of carbonic acid; and the second, requires you to infer that an acid will lower blood pH. Only one answer choice is both balanced correctly and gives an accurate change in pH. Although this knowledge is not required for the MCAT, your body constantly monitors blood pH to determine if concentrations of CO2 are too high, or alternatively, if O2 concentrations are too low.
Compare your answer with the correct one above
Given the above values of Ka, place the acids in order from strongest to weakest.
Given the above values of Ka, place the acids in order from strongest to weakest.
The acid dissociation constant, Ka, describes how strongly an acid tends to break apart into hydrogen ions (H+) and its conjugate base (A-). The higher the dissociation constant, the stronger the acid. HF has the largest Ka of these acids, making it the strongest, and H2CO3 has the smallest Ka, making it the weakest.
The acid dissociation constant, Ka, describes how strongly an acid tends to break apart into hydrogen ions (H+) and its conjugate base (A-). The higher the dissociation constant, the stronger the acid. HF has the largest Ka of these acids, making it the strongest, and H2CO3 has the smallest Ka, making it the weakest.
Compare your answer with the correct one above
What is the pH of a solution which has a hydroxide ion concentration of 5 * 10-4M?
What is the pH of a solution which has a hydroxide ion concentration of 5 * 10-4M?
First convert concentration of OH- into concentration of H+. Remember that Kw is 1*10-14.
Then, convert concentration of H+ into pH.
Alternatively, you can use the hydroxide concentration to solve for pOH and convert to pH.
First convert concentration of OH- into concentration of H+. Remember that Kw is 1*10-14.
Then, convert concentration of H+ into pH.
Alternatively, you can use the hydroxide concentration to solve for pOH and convert to pH.
Compare your answer with the correct one above
HCN dissociates based on the following reaction.
The Ka for hydrogen cyanide is .
What is the Kb for CN-?
HCN dissociates based on the following reaction.
The Ka for hydrogen cyanide is
What is the Kb for CN-?
Remember that the Ka for the acid and the Kb for the conjugate base, when multiplied will equal the autoionization of water constant (Kw).
Remember that the Ka for the acid and the Kb for the conjugate base, when multiplied will equal the autoionization of water constant (Kw).
Compare your answer with the correct one above
Compound Base strength, K b 1 1012 2 105 3 101 4 10-8
Students in a chemistry class are given one of four unknown samples in a laboratory. A student is told that his compound is the strongest acid of the four compounds. Based on the information in the above table, which compound was the student given?
| Compound | Base strength, K b |
|---|---|
| 1 | 1012 |
| 2 | 105 |
| 3 | 101 |
| 4 | 10-8 |
Students in a chemistry class are given one of four unknown samples in a laboratory. A student is told that his compound is the strongest acid of the four compounds. Based on the information in the above table, which compound was the student given?
The strongest acid of the group will also have the smallest Kb value. As the weakest base (smallest Kb), compound 4 will only partially dissociate in solution because it has a fairly strong conjugate acid. Were this question asking which base was the strongest, compound 1 would be the answer, due to its large Kb value.
The strongest acid of the group will also have the smallest Kb value. As the weakest base (smallest Kb), compound 4 will only partially dissociate in solution because it has a fairly strong conjugate acid. Were this question asking which base was the strongest, compound 1 would be the answer, due to its large Kb value.
Compare your answer with the correct one above