Acid-Base Reactions - AP Chemistry
Card 0 of 796
Which of the following would best buffer a solution from a pH of 4 to 6?
Which of the following would best buffer a solution from a pH of 4 to 6?
A weak acid/base best buffers about 1 pH point above and below its pKa. The pKA closest to the middle of 4 and 6 (so want as close to 5) is acetic acid at 4.7.
A weak acid/base best buffers about 1 pH point above and below its pKa. The pKA closest to the middle of 4 and 6 (so want as close to 5) is acetic acid at 4.7.
Compare your answer with the correct one above
A buffer using acetic acid (pKa=4.76) is titrated with NaOH. What is the pH at half the equivalence point?
A buffer using acetic acid (pKa=4.76) is titrated with NaOH. What is the pH at half the equivalence point?
The pH at half the equivalence point is equal to the pKa of the acid.
The pH at half the equivalence point is equal to the pKa of the acid.
Compare your answer with the correct one above
Which of the following solutions has the greatest buffering capacity?
Which of the following solutions has the greatest buffering capacity?
Nitric Acid is a strong acid and can't buffer. Rubidium Hydroxide is a strong base and thus can't buffer. Of the remaining, both are weak acids, but the one with a greater concentration has a greater buffering capacity.
Nitric Acid is a strong acid and can't buffer. Rubidium Hydroxide is a strong base and thus can't buffer. Of the remaining, both are weak acids, but the one with a greater concentration has a greater buffering capacity.
Compare your answer with the correct one above
To create a buffer solution, you can use a weak acid and .
To create a buffer solution, you can use a weak acid and .
The definition of a buffer solution is that it contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Since we are starting with a weak acid in this case, we need its conjugate base.
The definition of a buffer solution is that it contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Since we are starting with a weak acid in this case, we need its conjugate base.
Compare your answer with the correct one above
Which of the following can be used in a buffer solution?
Which of the following can be used in a buffer solution?
For a buffer solution, you need a weak acid and its conjugate base, or a weak base and its conjugate acid. HCO3 from the NaHCO3 and CO3– from K2CO3 are this pair.
For a buffer solution, you need a weak acid and its conjugate base, or a weak base and its conjugate acid. HCO3 from the NaHCO3 and CO3– from K2CO3 are this pair.
Compare your answer with the correct one above
Which of the following will increase the pH of an 
buffer solution?
I. Removing carbonic acid
II. Adding sodium bicarbonate
Which of the following will increase the pH of an
I. Removing carbonic acid
II. Adding sodium bicarbonate
To answer this question we need to look at the reaction below:
An increase in the pH will result in a decrease in the concentration of hydrogen ions (
). Using Le Chatelier’s principle we can find out which answer choices will decrease 
.
Removing carbonic acid will decrease the concentration of 
. To maintain equilibrium, the reaction will shift to the left and make more reactants from products; therefore, there will be a decrease in the 
and an increase in pH.
Recall that salts like sodium bicarbonate, or 
, will dissociate in water and form ions. Sodium bicarbonate will form sodium (
) and bicarbonate (
) ions. This side reaction will result in an increase in the bicarbonate ion concentration. Le Chatelier’s principle will shift the equilibrium of the given reaction to the left and, therefore, decrease the 
. Adding sodium bicarbonate will increase the pH.
To answer this question we need to look at the reaction below:
An increase in the pH will result in a decrease in the concentration of hydrogen ions (
Removing carbonic acid will decrease the concentration of
Recall that salts like sodium bicarbonate, or
Compare your answer with the correct one above
Which of the following combinations cannot be used to produce a buffer solution?
Which of the following combinations cannot be used to produce a buffer solution?
Buffer solutions can be made via two methods. The first method involves adding equal amounts of a weak acid and a salt of its weak conjugate base (or vice versa). The second methods involves adding a weak acid and a half equivalent of a strong base (or vice versa).
is a weak acid and 
is a salt of its weak conjugate base; therefore, this can form a buffer.
is a weak base and 
is a salt of its weak conjugate acid; this can also form a buffer. Note that this is the converse of the first method (weak base with salt of weak acid), but it can still form a buffer solution.
is a strong acid and 
is a weak base; therefore, adding 
and a half equivalent of 
will create a buffer solution. This is the converse of the second method (adding a weak base to a half equivalent of strong acid).
and 
are both strong reagents (acid and base, respectively); therefore, they cannot form a buffer solution.
Buffer solutions can be made via two methods. The first method involves adding equal amounts of a weak acid and a salt of its weak conjugate base (or vice versa). The second methods involves adding a weak acid and a half equivalent of a strong base (or vice versa).
Compare your answer with the correct one above
Blood is a physiological buffer. The carbonic acid/bicarbonate system maintains blood’s pH at around 7.35. Carbon dioxide in blood undergoes a complex equilibrium reaction as follows:
Alterations to carbon dioxide levels can change the blood pH.
A patient has abnormally low levels of carbon dioxide in the blood. What can you conclude about this patient?
Blood is a physiological buffer. The carbonic acid/bicarbonate system maintains blood’s pH at around 7.35. Carbon dioxide in blood undergoes a complex equilibrium reaction as follows:
Alterations to carbon dioxide levels can change the blood pH.
A patient has abnormally low levels of carbon dioxide in the blood. What can you conclude about this patient?
The question states that the patient has low levels of carbon dioxide. If we look at the given reaction, we will notice that the reaction will compensate for this by shifting the reaction equilibrium to the left. This phenomenon is called Le Chatelier’s principle and occurs to maintain the equilibrium of the reaction; therefore, the reaction will create more carbon dioxide by utilizing bicarbonate and hydrogen ions in the blood. A decrease in hydrogen ion concentration in blood will increase the pH and cause alkalosis (basicity in the blood). Since carbon dioxide is the cause of alkalosis, this patient will experience respiratory alkalosis. If he experienced alkalosis due to a change in bicarbonate ion concentration, the patient will have metabolic alkalosis.
The ratio of carbonic acid to bicarbonate will stay the same because both will be used in equal amounts (1:1 ratio) to produce carbon dioxide. Increasing respiratory rate, or hyperventilation, will result in an increase in the amount of carbon dioxide expelled by the patient; this will decrease the carbon dioxide concentration in the blood and will worsen the respiratory alkalosis. Recall that we are utilizing the bicarbonate ion (in conjunction with hydrogen ions) to create carbonic acid. The carbonic acid will be further broken down to replenish the carbon dioxide. A decrease in the bicarbonate concentration will slow down this process.
The question states that the patient has low levels of carbon dioxide. If we look at the given reaction, we will notice that the reaction will compensate for this by shifting the reaction equilibrium to the left. This phenomenon is called Le Chatelier’s principle and occurs to maintain the equilibrium of the reaction; therefore, the reaction will create more carbon dioxide by utilizing bicarbonate and hydrogen ions in the blood. A decrease in hydrogen ion concentration in blood will increase the pH and cause alkalosis (basicity in the blood). Since carbon dioxide is the cause of alkalosis, this patient will experience respiratory alkalosis. If he experienced alkalosis due to a change in bicarbonate ion concentration, the patient will have metabolic alkalosis.
The ratio of carbonic acid to bicarbonate will stay the same because both will be used in equal amounts (1:1 ratio) to produce carbon dioxide. Increasing respiratory rate, or hyperventilation, will result in an increase in the amount of carbon dioxide expelled by the patient; this will decrease the carbon dioxide concentration in the blood and will worsen the respiratory alkalosis. Recall that we are utilizing the bicarbonate ion (in conjunction with hydrogen ions) to create carbonic acid. The carbonic acid will be further broken down to replenish the carbon dioxide. A decrease in the bicarbonate concentration will slow down this process.
Compare your answer with the correct one above
A researcher is trying to make a buffer solution from a weak acid and its weak conjugate base. The pKa of the acid is 5.9 and the desired pH of the buffer solution is 3.5. Which of the following is the best way to make this buffer solution?
A researcher is trying to make a buffer solution from a weak acid and its weak conjugate base. The pKa of the acid is 5.9 and the desired pH of the buffer solution is 3.5. Which of the following is the best way to make this buffer solution?
One way to make a buffer is by adding equal amounts of a weak acid to its weak conjugate base. For example, you can add 1M acetic acid to 1M acetate to create a buffer solution (note that both acetic acid and its conjugate base (acetate) are weak). However, when using this method you have to remember that the desired pH of the buffer solution has to equal the pKa of the weak acid. The question states that the pKa of the acid is 5.9 and the desired pH of the buffer is 3.5; therefore, it is not possible to make the buffer with the given acid. The researcher would have to find another acid that has a pKa near 3.5.
One way to make a buffer is by adding equal amounts of a weak acid to its weak conjugate base. For example, you can add 1M acetic acid to 1M acetate to create a buffer solution (note that both acetic acid and its conjugate base (acetate) are weak). However, when using this method you have to remember that the desired pH of the buffer solution has to equal the pKa of the weak acid. The question states that the pKa of the acid is 5.9 and the desired pH of the buffer is 3.5; therefore, it is not possible to make the buffer with the given acid. The researcher would have to find another acid that has a pKa near 3.5.
Compare your answer with the correct one above
There are many solution systems which can only function as desired when the pH of that solution stays within a narrow range. Maintaining a stable pH in an unstable environment is most often achieved by the use of a buffer system, which is composed of a conjugate acid-base pair. One physiologically important buffer system is the bicarbonate buffer system that resists changes in blood pH.
The acid dissociation constant of carbonic acid 
The normal blood pH is tightly regulated between 7.35 and 7.45
When blood pH falls below 7.35 a person is said to have acidosis. Depending upon how far the pH drops, this condition could lead to nervous system impairment, coma, and death.
What is the ratio of bicarbonate ion concentration to carbonic acid concentration at which an individual will be at the threshold of experiencing acidosis 
There are many solution systems which can only function as desired when the pH of that solution stays within a narrow range. Maintaining a stable pH in an unstable environment is most often achieved by the use of a buffer system, which is composed of a conjugate acid-base pair. One physiologically important buffer system is the bicarbonate buffer system that resists changes in blood pH.
The acid dissociation constant of carbonic acid
The normal blood pH is tightly regulated between 7.35 and 7.45
When blood pH falls below 7.35 a person is said to have acidosis. Depending upon how far the pH drops, this condition could lead to nervous system impairment, coma, and death.
What is the ratio of bicarbonate ion concentration to carbonic acid concentration at which an individual will be at the threshold of experiencing acidosis
When performing acid/base calculations, the Henderson-Hasselbalch equation is useful:
To use this equation we need to convert the 
to the 
, and can use the following definition to do so:
Since an individual will begin experiencing acidosis when the blood falls below 7.35 we can use 7.35 as the pH in the Henderson-Hasselbalch equation. Adding in the 
of 6.10 calculated from the 
gives the equation below:
Plug in known values and solve:
Correct Answer:
The answer is unitless because 
all units cancel out.
When performing acid/base calculations, the Henderson-Hasselbalch equation is useful:
To use this equation we need to convert the
Since an individual will begin experiencing acidosis when the blood falls below 7.35 we can use 7.35 as the pH in the Henderson-Hasselbalch equation. Adding in the
Plug in known values and solve:
Correct Answer:
The answer is unitless because
Compare your answer with the correct one above
What is the pH of a solution that has \[OH-\] 1 X 10–4 M?
What is the pH of a solution that has \[OH-\] 1 X 10–4 M?
pOH would be 4 (use –log \[OH–\]) and pH would be 14–pOH = 14 – 4 = 10
pOH would be 4 (use –log \[OH–\]) and pH would be 14–pOH = 14 – 4 = 10
Compare your answer with the correct one above
What is the pH of a solution with \[OH-\] = 4 X 10-6
What is the pH of a solution with \[OH-\] = 4 X 10-6
\[OH-\] = 4 X 10-6
pOH = 5.4 — use –log \[OH–\] to find pOH
pH = 14– pOH = 8.6
\[OH-\] = 4 X 10-6
pOH = 5.4 — use –log \[OH–\] to find pOH
pH = 14– pOH = 8.6
Compare your answer with the correct one above
What is the pH of a soution containing .0001 M HCl?
What is the pH of a soution containing .0001 M HCl?
The pH of a solution is determined by taking the negative log of the concentration of hydrogen ions in solution. HCl is strong acid so it completely dissociates in solution. So adding .0001 M HCl is the same as saying that 1 *10-4 moles of H+ ions have been added to solution. The -log\[.0001\] =4, so the pH of the solution =4.
The pH of a solution is determined by taking the negative log of the concentration of hydrogen ions in solution. HCl is strong acid so it completely dissociates in solution. So adding .0001 M HCl is the same as saying that 1 *10-4 moles of H+ ions have been added to solution. The -log\[.0001\] =4, so the pH of the solution =4.
Compare your answer with the correct one above
What is the pOH of a solution that has a \[H+\] = 3.2 X 10-7 mol?
What is the pOH of a solution that has a \[H+\] = 3.2 X 10-7 mol?
\[H+\] = 3.2 X 10-7 mol
pH = -log \[H+\]
= 7 - log 3.2
= 7 -.505
=6.495
pOH = 14 - pH
= 7.5
\[H+\] = 3.2 X 10-7 mol
pH = -log \[H+\]
= 7 - log 3.2
= 7 -.505
=6.495
pOH = 14 - pH
= 7.5
Compare your answer with the correct one above
Which of the following solutions contains the greatest number of H+ ions?
Which of the following solutions contains the greatest number of H+ ions?
This question asks for the solution with the greatest number H+ ions, we can also approach this problem as if we are looking for the solution with the lowest pH. HCl is strong acid, therefore it will dissociate completely in solution. So the solution containing 0.010 mL of HCL contains 0.010 mL of H+ ions in solution, in addition to the H+ ions that are already in solution due to the auto-ionization of water. The only other solution that could have a pH less than 7 would be the one with 0.010 mL of CH3OH in excess water, becasue CH3OH is very slightly acidic. But since it is compared with an equal volume of HCl which is strong acid, it can be said that the most H+ ions will be found in the solution containing a small amount of strong acid, HCl.
This question asks for the solution with the greatest number H+ ions, we can also approach this problem as if we are looking for the solution with the lowest pH. HCl is strong acid, therefore it will dissociate completely in solution. So the solution containing 0.010 mL of HCL contains 0.010 mL of H+ ions in solution, in addition to the H+ ions that are already in solution due to the auto-ionization of water. The only other solution that could have a pH less than 7 would be the one with 0.010 mL of CH3OH in excess water, becasue CH3OH is very slightly acidic. But since it is compared with an equal volume of HCl which is strong acid, it can be said that the most H+ ions will be found in the solution containing a small amount of strong acid, HCl.
Compare your answer with the correct one above
What is the approximate pH of a 1.0 M solution of soluble CaCO3?
What is the approximate pH of a 1.0 M solution of soluble CaCO3?
Calcium carbonate is a base since it's the salt of a strong base (NaOH) and a weak acid (carbonic acid). The only basic pH on the list is 8, making it the correct answer.
Calcium carbonate is a base since it's the salt of a strong base (NaOH) and a weak acid (carbonic acid). The only basic pH on the list is 8, making it the correct answer.
Compare your answer with the correct one above
What is the pH of a 1 * 10–3M solution of H2CO3 acid? (pKa is 6.4)
What is the pH of a 1 * 10–3M solution of H2CO3 acid? (pKa is 6.4)
The –log of the pKa will give you the Ka, so take the –log (6.4), which gives you approximately 4 * 10–7. The Ka expression is set up with products over reactants (hydrogen carbonate ion * hydrogen ion/carbonic acid). The undissociated carbonic acid is 0.001M, and you should use the variable 'x' to account for how much it dissociates and how many of the ions are produced. Ka = 4 * 10–7 = x2/0.001 ends up being your Ka expression, if you assume x is negligible compared to the original concentration of 0.001. Solving for x, you get 2 * 10–5. This is the hydrogen ion concentration. pH = –log (hydrogen ion concentration), so pH = –long(2 * 10–5), which is approximately 4.7.
The –log of the pKa will give you the Ka, so take the –log (6.4), which gives you approximately 4 * 10–7. The Ka expression is set up with products over reactants (hydrogen carbonate ion * hydrogen ion/carbonic acid). The undissociated carbonic acid is 0.001M, and you should use the variable 'x' to account for how much it dissociates and how many of the ions are produced. Ka = 4 * 10–7 = x2/0.001 ends up being your Ka expression, if you assume x is negligible compared to the original concentration of 0.001. Solving for x, you get 2 * 10–5. This is the hydrogen ion concentration. pH = –log (hydrogen ion concentration), so pH = –long(2 * 10–5), which is approximately 4.7.
Compare your answer with the correct one above
If the Ksp of Mg(OH)2 is 1.2 * 10–11 and the magnesium ion concentration is 1.2 * 10–5M, at what pH does the Mg(OH)2 compound begin to precipitate?
If the Ksp of Mg(OH)2 is 1.2 * 10–11 and the magnesium ion concentration is 1.2 * 10–5M, at what pH does the Mg(OH)2 compound begin to precipitate?
The expression for Ksp is Ksp = \[Mg2+\]\[OH–\]2.
Thus, \[OH–\] = √(1.2 * 10–11)/(1.2 * 10–5)
\[OH–\] = 1 * 10–3
Thus, pH = –log(1 X 10–3) = 3
pH = 14 – 3 = 11
The expression for Ksp is Ksp = \[Mg2+\]\[OH–\]2.
Thus, \[OH–\] = √(1.2 * 10–11)/(1.2 * 10–5)
\[OH–\] = 1 * 10–3
Thus, pH = –log(1 X 10–3) = 3
pH = 14 – 3 = 11
Compare your answer with the correct one above
What is the range of possible hydrogen ion concentrations in acidic solution?
What is the range of possible hydrogen ion concentrations in acidic solution?
For a solution to be acidic, it must have a pH between 1 and 6.99, since 7 is neutral; pH is –log(hydrogen ion concentration), the range of possible values is between 10–1 and 10–6.999.
For a solution to be acidic, it must have a pH between 1 and 6.99, since 7 is neutral; pH is –log(hydrogen ion concentration), the range of possible values is between 10–1 and 10–6.999.
Compare your answer with the correct one above
What is the range of possible hydrogen ion concentrations in basic solution?
What is the range of possible hydrogen ion concentrations in basic solution?
For a solution to be basic, it must have a pH between 8 and 14, since 7 is neutral; pH is –log(hydrogen ion concentration); the range of possible values is between 10–13 and 10–7.001.
For a solution to be basic, it must have a pH between 8 and 14, since 7 is neutral; pH is –log(hydrogen ion concentration); the range of possible values is between 10–13 and 10–7.001.
Compare your answer with the correct one above