Henderson–Hasselbalch equation Knowledge-Based Download PDF

Questions

1. 1.

   A buffer solution has a pH of 4.20 and is prepared from a weak acid, $\text{HA}$ ($pK_a = 4.80$), and its conjugate base, $\text{A}^-$. If the total concentration of the buffer components ($[\text{HA}] + [\text{A}^-]$) is 0.20 M, what is the concentration of $\text{A}^-$ in the solution? (Given: $\log 2 \approx 0.30$)

   • A) 0.16 M
   • B) 0.10 M
   • C) 0.040 M
   • D) 0.050 M
2. 2.

   A buffer solution contains 0.050 mol of a weak acid $\text{HA}$ ($pK_a = 6.80$) and 0.050 mol of its conjugate base $\text{A}^-$ in 1.0 L of water. What is the pH of the solution after 0.010 mol of solid $\text{NaOH}$ is added without changing the total volume? (Given: $\log 1.5 \approx 0.18$)

   • A) 6.62
   • B) 6.80
   • C) 6.98
   • D) 7.10
3. 3.

   A buffer solution containing 0.12 M of a weak acid, $\text{HA}$, and 0.030 M of its conjugate base, $\text{A}^-$, has a pH of 3.80. What is the acid dissociation constant ($K_a$) of $\text{HA}$? (Given: $\log 2 \approx 0.30$)

   • A) $6.3 \times 10^{-4}$
   • B) $2.5 \times 10^{-5}$
   • C) $4.0 \times 10^{-5}$
   • D) $1.6 \times 10^{-4}$
4. 4.

   What molar ratio of sodium acetate ($\text{CH}_3\text{COONa}$) to acetic acid ($\text{CH}_3\text{COOH}$) is required to prepare a buffer solution with a pH of 5.05? (Assume the $pK_a$ of acetic acid is 4.75 and $10^{0.30} \approx 2.0$.)

   • A) 0.30
   • B) 0.50
   • C) 2.0
   • D) 3.3
5. 5.

   A buffer solution is prepared by mixing 0.20 M nitrous acid ($\text{HNO}_2$, $K_a = 4.0 \times 10^{-4}$) and 0.50 M sodium nitrite ($\text{NaNO}_2$). What is the pH of this buffer solution? (Given: $\log 2 \approx 0.30$, $\log 2.5 \approx 0.40$)

   • A) 3.00
   • B) 3.40
   • C) 3.60
   • D) 3.80