Question 1

Which of the following best describes the function of a buffer solution as illustrated in the diagram above?

Accepted Answer

A buffer solution resists changes in pH by converting added strong acids or bases into weak acids or bases, as shown by the shift in the relative amounts of CH$$_3$$COOH and CH$$_3$$COO$$^-.$$

Question 2

According to the diagram, what happens to the concentrations of CH$$_3$$COOH and CH$$_3$$COO$$^-$$ when a strong acid (H$$_3O$^+) is $$added to the buffer solution?

Accepted Answer

The concentration of CH$$_3$$COOH increases and the concentration of CH$$_3$$COO$$^-$$ decreases.

Question 3

What is the chemical equation that represents the buffer system shown in the diagram?

Accepted Answer

$$\mathrm{CH_3COOH(aq) + H_2O(l) \rightleftharpoons H_3O^+(aq) + CH_3COO^-(aq)}$$

Question 4

If a strong base (OH$$^-) is $$added to the buffer solution, as shown in the diagram, what is the immediate effect on the buffer components?

Accepted Answer

CH$$_3$$COOH is converted to CH$$_3$$COO$$^-$$, increasing the concentration of CH$$_3$$COO$$^-$$ and decreasing CH$$_3$$COOH.

Question 5

Which equation correctly represents the Henderson-Hasselbalch equation for the buffer system in the diagram?

Accepted Answer

$$\mathrm{pH = pK_a + \log \frac{[CH_3COO^-]}{[CH_3COOH]}}$$

Question 6

Why does the buffer solution in the diagram not experience a large change in pH upon addition of a small amount of strong acid or base?

Accepted Answer

Because the buffer components react with the added acid or base, converting them into weak acid or base forms and minimizing the change in [H$$^+$$].

Question 7

If the buffer solution in the diagram originally contains 0.10 M CH$$_3$$COOH and 0.10 M CH$$_3$$COO$$^-$$, what is the pH if the $$K_a of $$acetic acid is $$1.8 	imes 10$$^{-5}$$?

Accepted Answer

$$\mathrm{pH = 4.74}$$

Question 8

What is the main reason a buffer solution loses its ability to resist pH changes when too much strong acid or base is added?

Accepted Answer

The buffer components are consumed, and the solution no longer contains significant amounts of both the weak acid and its conjugate base.

Question 9

Which of the following best describes the common ion effect as it relates to the buffer system in the diagram?

Accepted Answer

Adding sodium acetate (NaCH$$_3$$COO) to acetic acid suppresses the ionization of acetic acid, decreasing [H$$^+$$].

Question 10

A buffer is most effective when the concentrations of acid and conjugate base are:

Accepted Answer

Approximately equal, so that the ratio $$\frac{[A^-]}{[HA]} is $$close to 1.

Question 11

If you want to prepare a buffer with a pH of 5.00 using acetic acid ($$pK_a = 4.74$$), what should the ratio $$\frac{[CH_3COO^-]}{[CH_3COOH]} be$$?

Accepted Answer

$$\mathrm{1.82}$$

Question 12

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity is greatest when the concentrations of acid and conjugate base are high and nearly equal.

Question 13

Which of the following is a real-life example of a buffer system in the human body?

Accepted Answer

$$\mathrm{H_2CO_3 \rightleftharpoons H^+ + HCO_3^-} ($$carbonic acid/bicarbonate buffer in blood plasma)

Buffer Solutions and the Common Ion Effect: Structure, Function, and Calculations

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