Question 1

The pK_a of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 2.0 M and the sodium lactate concentration is 0.50 M? A) 2.86 B) 3.26 C) 4.46 D) 4.86

Accepted Answer

The pH of the buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base (sodium lactate in this case) and [HA] is the concentration of the acid (lactic acid). Substituting the given values: pH = 3.86 + log(0.50/2.0) = 3.86 - 0.60 = 3.26.

Question 2

Which of the following is true of a buffer prepared with equal concentrations of an acid and its conjugate base? A) pH = 7 B) pH = pK_a C) The pH depends on the concentration of the buffer. D) none of the above

Accepted Answer

A buffer prepared with equal concentrations of an acid and its conjugate base has a pH equal to the pKa of the weak acid component. Therefore, the pH can be calculated as pK_a, where K_a is the pKa of the weak acid. It does not depend on the concentration of the buffer.

Question 3

Increasing which of the following will increase the pH of a buffer made using acetic acid and sodium acetate? A) the amount of water present B) the [C2H3O2^-] C) the [HC₂H₃O₂] D) both the [C2H3O2^-] and [HC2H3O2]

Accepted Answer

Increasing the concentration of the acetate ion ([C2H3O2^-]) will increase the pH of the buffer, as it will shift the equilibrium towards the formation of more acetic acid, reducing the concentration of hydrogen ions.

Question 4

Which of the following buffers will have the lowest pH? A) a solution containing 0.20 M HC₂H₃O₂ and 0.20 M NaC₂H₃O₂ B) a solution containing 0.25 M HC₂H₃O₂ and 0.15 M NaC₂H₃O₂ C) a solution containing 0.15 M HC₂H₃O₂ and 0.25 M NaC₂H₃O₂ D) They all have the same pH.

Accepted Answer

The buffer with the lowest pH will have a higher concentration of the weak acid (HC2H3O2) relative to its conjugate base (NaC2H3O2). Option B has a higher concentration of the acid (0.25 M) compared to the base (0.15 M), resulting in a lower pH.

Question 5

Human blood contains which of the following buffers? A) H₂CO₃/HCO₃^- B) H₂PO₄^-/HPO₄^2- C) both a and b D) neither a nor b

Accepted Answer

Human blood contains both the bicarbonate buffer system (H2CO3/HCO3-) and the phosphate buffer system (H2PO4-/HPO4^2-), which help maintain pH balance.

Question 6

Which of the following species has the largest concentration in buffering systems of human blood? A) H₂CO₃ B) HCO₃^- C) H₂PO₄^- D) HPO₄^2-

Accepted Answer

Bicarbonate (HCO₃⁻) is the predominant buffer in human blood, playing a crucial role in maintaining pH balance.

Question 7

As given in the text, which of the following appears in the numerator of the fractional term of the Henderson-Hasselbalch equation?
A) the amount of the conjugate base
B) the amount of weak acid
C) the concentration of conjugate base
D) the concentration of weak acid

Accepted Answer

The Henderson-Hasselbalch equation is pH = pKa + log([conjugate base]/[weak acid]), where the concentration of the conjugate base appears in the numerator.

Question 8

Which of the following buffers will have the lowest pH? A) a solution containing 0.10 M HC₂H₃O₂ and 0.10 M NaC₂H₃O₂ B) a solution containing 0.20 M HC₂H₃O₂ and 0.20 M NaC₂H₃O₂ C) a solution containing 0.30 M HC₂H₃O₂ and 0.30 M NaC₂H₃O₂ D) They all have the same pH.

Accepted Answer

The pH of a buffer solution depends on the ratio of the concentrations of the acid and its conjugate base, not their absolute concentrations. Since all solutions have the same ratio of HC2H3O2 to NaC2H3O2, they all have the same pH.

Question 9

Which of the following buffers will have the highest pH? A) a solution containing 0.20 M HC₂H₃O₂ and 0.20 M NaC₂H₃O₂ B) a solution containing 0.25 M HC₂H₃O₂ and 0.15 M NaC₂H₃O₂ C) a solution containing 0.15 M HC₂H₃O₂ and 0.25 M NaC₂H₃O₂ D) They all have the same pH.

Accepted Answer

The buffer with the highest pH will have a higher concentration of the conjugate base (NaC₂) compared to the acid (HC₂H₃O₂). Therefore, option C, which has a higher concentration of NaC₂, will have a higher pH compared to the other options.

Question 10

Human blood contains which of the following buffers? A) H₂CO₂/HCO₃^- B) HC₂H₃O₂/C₂H₃O₂^- C) both a and b D) neither a nor b

Accepted Answer

The primary buffer system in human blood is the bicarbonate buffer system, which consists of carbonic acid (H2CO3) and bicarbonate ions (HCO3-).

Question 11

Which of the following will determine the pH of a buffer made using acetic acid and sodium acetate? A) the amount of water present B) the [C₂H₃O₂-] C) the [HC₂H₃O₂] D) the ratio [C2H3O2^-]/[HC2H3O2]

Accepted Answer

The pH of a buffer made using acetic acid and sodium acetate is determined by the ratio of the concentrations of the conjugate base (C2H3O2-) and the weak acid (HC2H3O2). This is represented by the expression [C2H3O2-]/[HC2H3O2]. This ratio is equivalent to the expression [CS-]/[HS], where CS- is the concentration of the conjugate base (sodium acetate) and HS is the concentration of the weak acid (acetic acid). Therefore, the best choice is D, which represents the ratio [C2H3O2-]/[HC2H3O2]. The other options (A, B, and C) are not relevant to determining the pH of a buffer made using acetic acid and sodium acetate.

Question 12

The pK_a of acetic acid, HC₂H₃O₂, is 4.75. What is the pH of a buffer in which [HC₂H₃O₂] = 0.20 M and [NaC₂H₃O₂] = 2.0 M? A) 3.75 B) 4.75 C) 5.75 D) 7.00

Accepted Answer

To calculate the pH of a buffer, we use the Henderson-Hasselbalch equation: pH = pK_a + log([A-]/[HA]) where [HA] is the concentration of the weak acid (acetic acid in this case) and [A-] is the concentration of its conjugate base (acetate ion in this case). First, we need to calculate the concentrations of [HA] and [A-]. Since the buffer is made up of acetic acid and its conjugate base (sodium acetate), we need to use the dissociation constants of both species. The dissociation constant for acetic acid is given in the problem statement as pK_a = 4.75. We can use this value to calculate the dissociation constant for the acetate ion: pK_a + pOH = pKw 4.75 + pOH = 14.00 pOH = 9.25 pOH = -log[OH-] [OH-] = 10^-pOH = 5.6 x 10^-10 Kb = Kw/Ka = 1.0 x 10^-14/1.8 x 10^-5 = 5.6 x 10^-10 Now we can use the concentrations of the two species to calculate the pH: [HA] = 0.20 M (from the problem statement) [A-] = 2.0 M (from the problem statement) pH = 4.75 + log(2.0/0.20) pH = 5.75 Therefore, the pH of the buffer is 5.75, which is closest to choice (C).

Question 13

Which of the following buffers will have the best buffer capacity? A) a solution containing 0.1 M HC₂H₃O₂ and 0.1 M NaC₂H₃O₂ B) a solution containing 0.05 M HC₂H₃O₂ and 0.15 M NaC₂H₃O₂ C) a solution containing 0.15 M HC₂H₃O₂ and 0.05 M NaC₂H₃O₂ D) They all have the same buffer capacity.

Accepted Answer

A buffer has the best capacity when the concentrations of the acid and its conjugate base are equal, as in option A.

Question 14

Human blood contains which of the following buffers? A) HC₂H₃O₂/C₂H₃O₂^- B) H₂PO₄^-/HPO₄^2- C) both a and b D) neither a nor b

Accepted Answer

The primary buffer system in human blood is the bicarbonate buffer system, but the phosphate buffer system (H2PO4-/HPO4^2-) also plays a role in maintaining pH balance. The acetate buffer (HC2H3O2/C2H3O2-) is not a significant buffer in human blood.

Question 15

Which of the following is true of a buffer prepared with equal concentrations of an acid and its conjugate base?
A) The buffer capacity depends on the concentration of the acid and base
B) The pH depends on the concentration of the buffer
C) both a and b
D) neither a nor b

Accepted Answer

The buffer capacity is influenced by the concentration of the acid and base, as higher concentrations can neutralize more added acid or base. The pH of the buffer, however, is determined by the pKa of the acid and the ratio of the concentrations of the acid and its conjugate base, not the overall concentration of the buffer.

Question 16

Increasing which of the following will decrease the buffer capacity of a buffer made using acetic acid and sodium acetate? A) the amount of water present B) the [C₂H₃O₂^-] C) the [HC₂H₃O₂] D) the ratio [C₂H₃O₂^-]/[HC₂H₃O₂]

Accepted Answer

The buffer capacity of a buffer solution is directly related to the concentrations of the acid and its conjugate base. Increasing the amount of water present in the buffer solution will dilute the concentrations of both acetic acid and sodium acetate, leading to a decrease in buffer capacity. Thus, choice A is the correct answer. B and C are not relevant factors for calculating buffer capacity. D is an inverse relationship between the concentrations of the acid and its conjugate base, so it does not address a factor that could positively or negatively impact buffer capacity.

Question 17

As given in the text, which of the following appears in the denominator of the fractional term of the Henderson-Hasselbalch equation?
A) the amount of the conjugate base
B) the amount of weak acid
C) the concentration of conjugate base
D) the concentration of weak acid

Accepted Answer

The concentration of weak acid appears in the denominator of the fractional term of the Henderson-Hasselbalch equation.

Question 18

The pK_a of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 0.20 M and the sodium lactate concentration is 2.0 M? A) 2.86 B) 3.86 C) 4.86 D) 7.00

Accepted Answer

The Henderson-Hasselbalch equation for a buffer is pH = pKa + log([base]/[acid]).
In this case, the acid is lactic acid and the base is sodium lactate. 
pKa = 3.86
[base]/[acid] = 2.0/0.20 = 10
pH = 3.86 + log(10) = 4.86. 
Therefore, the pH of the buffer is 4.86, which corresponds to choice C.

Question 19

The pK_a of acetic acid, HC₂H₃O₂, is 4.75. What is the pH of a buffer in which [HC₂H₃O₂] = 2.0 M and [NaC₂H₃O₂] = 0.20 M? A) 3.75 B) 4.75 C) 5.75 D) 7.00

Accepted Answer

The answer of The pK_a of acetic acid, HC₂H₃O₂, is...

Question 20

Increasing which of the following will decrease the pH of a buffer made using acetic acid and sodium acetate? A) the amount of water present B) the [C2H3O2^-] C) the [HC₂H₃O₂] D) the ratio [C2H3O2^-]/[HC2H3O2]

Accepted Answer

Increasing the concentration of acetic acid (HC2H3O2) will increase the concentration of hydrogen ions, thus decreasing the pH of the buffer solution.

Quiz 8: Acids and Bases

The pKa of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 2.0 M and the sodium lactate concentration is 0.50 M?

Which of the following is true of a buffer prepared with equal concentrations of an acid and its conjugate base?

Increasing which of the following will increase the pH of a buffer made using acetic acid and sodium acetate?

Which of the following buffers will have the lowest pH?

Human blood contains which of the following buffers?

Which of the following species has the largest concentration in buffering systems of human blood?

As given in the text, which of the following appears in the numerator of the fractional term of the Henderson-Hasselbalch equation?

Which of the following buffers will have the lowest pH?

Which of the following buffers will have the highest pH?

Human blood contains which of the following buffers?

Which of the following will determine the pH of a buffer made using acetic acid and sodium acetate?

The pKa of acetic acid, HC2H3O2, is 4.75. What is the pH of a buffer in which [HC2H3O2] = 0.20 M and [NaC2H3O2] = 2.0 M?

Which of the following buffers will have the best buffer capacity?

Human blood contains which of the following buffers?

Which of the following is true of a buffer prepared with equal concentrations of an acid and its conjugate base?

Increasing which of the following will decrease the buffer capacity of a buffer made using acetic acid and sodium acetate?

As given in the text, which of the following appears in the denominator of the fractional term of the Henderson-Hasselbalch equation?

The pKa of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 0.20 M and the sodium lactate concentration is 2.0 M?

The pKa of acetic acid, HC2H3O2, is 4.75. What is the pH of a buffer in which [HC2H3O2] = 2.0 M and [NaC2H3O2] = 0.20 M?

Increasing which of the following will decrease the pH of a buffer made using acetic acid and sodium acetate?

The pK_a of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 2.0 M and the sodium lactate concentration is 0.50 M?

The pK_a of acetic acid, HC₂H₃O₂, is 4.75. What is the pH of a buffer in which [HC₂H₃O₂] = 0.20 M and [NaC₂H₃O₂] = 2.0 M?

The pK_a of lactic acid is 3.86. What is the pH of a buffer in which the lactic acid concentration is 0.20 M and the sodium lactate concentration is 2.0 M?

The pK_a of acetic acid, HC₂H₃O₂, is 4.75. What is the pH of a buffer in which [HC₂H₃O₂] = 2.0 M and [NaC₂H₃O₂] = 0.20 M?