Henderson–Hasselbalch equation Knowledge-Based Practice

Questions

1. 1.

   A 500 mL buffer solution contains 0.12 mol of a monoprotic weak acid, $\text{HA}$, and 0.48 mol of its conjugate base, $\text{A}^-$. If the measured pH of this buffer solution is 5.30, what is the $\text{p}K_a$ of the weak acid? (Assume $\log 2 = 0.30$)

   • A) 5.90
   • B) 5.60
   • C) 5.00
   • D) 4.70
2. 2.

   A 1.0 L buffer solution contains 0.30 mol of a weak acid, $\text{HA}$ ($\text{p}K_a = 5.00$), and 0.30 mol of its conjugate base, $\text{A}^-$. What is the pH of the solution after 0.10 mol of solid $\text{NaOH}$ is added without changing the total volume? (Assume $\log 2 = 0.30$)

   • A) 4.70
   • B) 5.30
   • C) 5.18
   • D) 5.00
3. 3.

   A buffer solution is prepared using nitrous acid, $\text{HNO}_2$ ($\text{p}K_a = 3.40$), and potassium nitrite, $\text{KNO}_2$. If the measured pH of the buffer solution is 2.40, what is the concentration ratio of weak acid to conjugate base, $[\text{HNO}_2] / [\text{NO}_2^-]$?

   • A) 0.010
   • B) 0.10
   • C) 1.0
   • D) 10
4. 4.

   A buffer solution with a pH of 9.55 is prepared using a weak acid, $\text{HA}$ ($\text{p}K_a = 9.25$), and its conjugate base, $\text{A}^-$. If the concentration of $\text{HA}$ in the buffer is 0.15 M, what is the concentration of $\text{A}^-$ in this solution?

   • A) 0.075 M
   • B) 0.15 M
   • C) 0.20 M
   • D) 0.30 M
5. 5.

   A buffer solution contains 0.20 M of a weak acid, $\text{HA}$ ($\text{p}K_a = 4.80$), and 0.020 M of its conjugate base, $\text{A}^-$. What is the pH of this buffer solution?

   • A) 5.80
   • B) 4.80
   • C) 4.00
   • D) 3.80

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