Ka and Kb Knowledge-Based Download PDF

Questions

1. 1.

   What is the pH of a 0.10 M aqueous solution of a weak base, B, with a base dissociation constant of $K_b = 1.0 \times 10^{-5}$ at 25 °C?

   • A) 3.00
   • B) 8.00
   • C) 9.00
   • D) 11.00
2. 2.

   A 0.10 M aqueous solution of a weak monoprotic acid, HA, has a pH of 4.00 at 25 °C. What is the acid dissociation constant, $K_a$, of this acid?

   • A) $1.0 \times 10^{-7}$
   • B) $1.0 \times 10^{-4}$
   • C) $1.0 \times 10^{-8}$
   • D) $1.0 \times 10^{-3}$
3. 3.

   What is the equilibrium constant, $K$, at 25 °C for the reaction $HF(aq) + NH_3(aq) \rightleftharpoons F^-(aq) + NH_4^+(aq)$, given that $K_a(HF) = 6.8 \times 10^{-4}$ and $K_b(NH_3) = 1.8 \times 10^{-5}$?

   • A) $3.8 \times 10^1$
   • B) $1.2 \times 10^{-8}$
   • C) $8.2 \times 10^{-7}$
   • D) $1.2 \times 10^6$
4. 4.

   The acid dissociation constants for four weak monoprotic acids at 25 °C are given as $HX$ ($K_a = 7.2 \times 10^{-4}$), $HY$ ($K_a = 3.5 \times 10^{-11}$), $HZ$ ($K_a = 1.8 \times 10^{-5}$), and $HQ$ ($K_a = 4.9 \times 10^{-8}$). Which of the conjugate bases has the largest base dissociation constant ($K_b$) at this temperature?

   • A) $X^-$
   • B) $Y^-$
   • C) $Z^-$
   • D) $Q^-$
5. 5.

   Hypochlorous acid ($HClO$) has an acid dissociation constant of $K_a = 3.0 \times 10^{-8}$ at 25 °C. What is the value of the base dissociation constant ($K_b$) for its conjugate base, the hypochlorite ion ($ClO^-$), at the same temperature?

   • A) $3.0 \times 10^{-6}$
   • B) $3.0 \times 10^{-22}$
   • C) $3.3 \times 10^{-7}$
   • D) $3.3 \times 10^{-8}$