14.6 Buffers

Explain why the pH does not change significantly when a small amount of an acid or a base is added to a solution that contains equal amounts of the acid H₃PO₄ and a salt of its conjugate base NaH₂PO₄.

What is [H₃O⁺] in a solution of 0.25 M CH₃CO₂H and 0.030 M NaCH₃CO₂?
$\text{CH}_{3} \text{CO}_{2} \text{H} \left(a q\right) + \text{H}_{2} \text{O} \left(l\right) \rightleftharpoons \text{H}_{3} \text{O}^{+} \left(a q\right) + \text{CH}_{3} \text{CO}_{2} ^{−} \left(a q\right) K_{\text{a}} = 1.8 \times 10^{−5}$

What is [OH⁻] in a solution of 0.125 M CH₃NH₂ and 0.130 M CH₃NH₃Cl?
$\text{CH}_{3} \text{NH}_{2} \left(a q\right) + \text{H}_{2} \text{O} \left(l\right) \rightleftharpoons \text{CH}_{3} \text{NH}_{3} ^{+} \left(a q\right) + \text{OH}^{−} \left(a q\right) K_{\text{b}} = 4.4 \times 10^{−4}$

What is the effect on the concentration of acetic acid, hydronium ion, and acetate ion when the following are added to an acidic buffer solution of equal concentrations of acetic acid and sodium acetate:

(a) HCl

(b) KCH₃CO₂

(c) NaCl

(d) KOH

(e) CH₃CO₂H

What will be the pH of a buffer solution prepared from 0.20 mol NH₃, 0.40 mol NH₄NO₃, and just enough water to give 1.00 L of solution?

How much solid NaCH₃CO₂•3H₂O must be added to 0.300 L of a 0.50-M acetic acid solution to give a buffer with a pH of 5.00? (Hint: Assume a negligible change in volume as the solid is added.)

A buffer solution is prepared from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate. Use 1.80 $\times$ 10⁻⁵ as K_a for acetic acid.

(a) What is the pH of the solution?

(b) Is the solution acidic or basic?

(c) What is the pH of a solution that results when 3.00 mL of 0.034 M HCl is added to 0.200 L of the original buffer?