Question 1

Which of the following best describes the function of a buffer solution?

Accepted Answer

A buffer solution maintains a constant pH when small amounts of strong acid or base are added.

Question 2

Which equation represents the equilibrium of a weak acid buffer system?

Accepted Answer

$$\mathrm{HA} \rightleftharpoons \mathrm{H}^+ + \mathrm{A}^-$$

Question 3

A buffer is made from acetic acid and acetate ion. Which of the following is true when a small amount of NaOH is added?

Accepted Answer

The pH remains nearly constant.

Question 4

Which of the following pairs can be used to make a buffer solution?

Accepted Answer

Weak acid and its conjugate base

Question 5

What is the pH of a PBS buffer after adding 10.0 mL of 0.10 M NaOH to 1.000 L of PBS buffer, given $$[\mathrm{HPO}_4$$^{2-}$$] = 0.00822\,\mathrm{M}$$, $$[\mathrm{H}_2\mathrm{PO}_4^-] = 0.00356\,\mathrm{M}$$, and $$K_a = 6.2 	imes 10$$^{-8}$$?

Accepted Answer

$$pH = 7.57$$

Question 6

Which of the following is a common biological buffer and its main purpose?

Accepted Answer

Phosphate Buffered Saline (PBS); maintains stable pH and salt concentration in biological samples.

Question 7

If you add a strong acid to a buffer, what happens to the concentration of the conjugate base?

Accepted Answer

It decreases.

Question 8

Given the buffer reaction $$\mathrm{H}_2\mathrm{PO}_4^- + \mathrm{OH}^- \rightarrow \mathrm{HPO}_4$$^{2-}$$ + \mathrm{H}_2\mathrm{O}$$, what is the effect of adding NaOH to PBS buffer?

Accepted Answer

The concentration of $$\mathrm{HPO}_4$$^{2-}$$ increases.

Question 9

Which formula is used to calculate the pH of a buffer solution after addition of acid or base?

Accepted Answer

$$pH = -\log[\mathrm{H}^+]$$

Question 10

Which of the following is NOT a property of a buffer solution?

Accepted Answer

Maintains pH even after large amounts of acid or base are added.

Question 11

A buffer solution initially contains 100 molecules of HA. After adding 40 molecules of NaOH, what is the main chemical reaction occurring?

Accepted Answer

$$\mathrm{OH}^- + \mathrm{HA} \rightarrow \mathrm{A}^- + \mathrm{H}_2\mathrm{O}$$

Question 12

Which buffer pair would be most effective at maintaining a pH near 7.2?

Accepted Answer

Dihydrogen phosphate/hydrogen phosphate ($$pK_a = 7.21)$$

Question 13

What is the effect of adding a large amount of strong acid to a buffer solution?

Accepted Answer

The buffer will eventually lose its ability to resist pH change.

Question 14

Which of the following is the correct $$K_a$$ expression for the equilibrium $$\mathrm{H}_2\mathrm{PO}_4^- \rightleftharpoons \mathrm{H}^+ + \mathrm{HPO}_4$$^{2-}$$?

Accepted Answer

$$K_a = \frac{[\mathrm{H}^+][\mathrm{HPO}_4$$^{2-}$$]}{[\mathrm{H}_2\mathrm{PO}_4^-]}$$

Question 15

Why is PBS buffer used in immunoassays such as ELISA?

Accepted Answer

It prevents antibody denaturation by maintaining stable pH.

Question 16

If you add 10.0 mL of 0.10 M HCl to 1.000 L of PBS buffer, what is the new pH, given $$[\mathrm{H}_2\mathrm{PO}_4^-] = 0.00554\,\mathrm{M}$$, $$[\mathrm{HPO}_4$$^{2-}$$] = 0.00624\,\mathrm{M}$$, and $$K_a = 6.2 	imes 10$$^{-8}$$?

Accepted Answer

$$pH = 7.26$$

Question 17

Which step is NOT part of the process for calculating the pH of a buffer after addition of acid or base?

Accepted Answer

Ignore the change in volume after addition.

Question 18

A buffer solution is prepared using lactic acid and lactate ion. If the $$K_a of $$lactic acid is $$1.4 	imes 10$$^{-4}$$, what is its pK_a$?

Accepted Answer

$$pK_a = 3.85$$

Buffers: Composition, Function, and pH Calculations

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