Buffers Knowledge-Based Practice

Questions

1. 1.

   Which of the following weak acids, when paired with its conjugate base, is most suitable for preparing an aqueous buffer solution with a target pH of 5.00?

   • A) Hypochlorous acid, $\text{HClO}$ ($K_a = 3.0 \times 10^{-8}$)
   • B) Formic acid, $\text{HCOOH}$ ($K_a = 1.8 \times 10^{-4}$)
   • C) Acetic acid, $\text{CH}_3\text{COOH}$ ($K_a = 1.8 \times 10^{-5}$)
   • D) Hydrocyanic acid, $\text{HCN}$ ($K_a = 6.2 \times 10^{-10}$)
2. 2.

   Two separate buffer solutions, X and Y, are prepared using the same weak acid, $\text{HA}$, and its conjugate base salt, $\text{NaA}$. Solution X contains 0.50 M $\text{HA}$ and 0.50 M $\text{NaA}$, whereas Solution Y contains 0.050 M $\text{HA}$ and 0.050 M $\text{NaA}$. Which of the following statements correctly compares Solution X to Solution Y?

   • A) Solution X has a lower pH than Solution Y, but both solutions have identical buffer capacities.
   • B) Solution X has a higher pH and a greater buffer capacity than Solution Y.
   • C) Solution X has the same initial pH and the same buffer capacity as Solution Y because their component ratios are identical.
   • D) Solution X has the same initial pH as Solution Y, but Solution X has a greater buffer capacity.
3. 3.

   A buffer solution is prepared containing equal concentrations of a weak acid, $\text{HA}$, and its conjugate base, $\text{A}^-$. Which of the following statements correctly describes what occurs when this buffer is diluted tenfold with distilled water?

   • A) Its pH increases by 1, while its buffer capacity remains unchanged.
   • B) Its pH remains essentially unchanged, while its buffer capacity decreases.
   • C) Its pH decreases by 1, while its buffer capacity increases.
   • D) Both its pH and its buffer capacity remain completely unchanged.
4. 4.

   When a small amount of hydrochloric acid is added to an aqueous buffer containing equimolar amounts of nitrous acid ($\text{HNO}_2$) and potassium nitrite ($\text{KNO}_2$), which species primarily consumes the added hydronium ions?

   • A) $\text{HNO}_2$
   • B) $\text{NO}_2^-$
   • C) $\text{K}^+$
   • D) $\text{OH}^-$
5. 5.

   Which of the following aqueous mixtures acts as an effective buffer solution?

   • A) 0.10 M $\text{HCl}$ and 0.10 M $\text{NaCl}$
   • B) 0.10 M $\text{NaOH}$ and 0.10 M $\text{NH}_3$
   • C) 0.10 M $\text{CH}_3\text{COOH}$ and 0.10 M $\text{CH}_3\text{COONa}$
   • D) 0.10 M $\text{HNO}_3$ and 0.10 M $\text{KNO}_3$

Answers and step-by-step solutions appear after you finish the test.