Question

If the base-dissociation constant, Kb, for a substance is 4.3 x 10^–10, what does this tell you about Ka?
A) Ka = 2.3 x 10^–5
B) Ka = 1.0 x 10^–4
C) Ka = 2.3 x 10^2
D) Ka = 1.0 x 10^3

Answer 1

Ka*Kb=Kw=10^-14
Ka=10^-14/(4.3*10^-10) (at 25°C)
=2.3*10^-5 (A)

Answer 2

Answer: The correct answer is option (A) $K_a=2.3\times 10^{-5}$

Explanation:

$K_b=4.3\times 10^{-5}$

$K_w=1\times 10^{-14}$

The relation between $K_w,K_a and K_b$ is given as:

$K_w=K_a\times K_b$

$K_a=\frac{K_w}{K_b}=\frac{1\times 10^{-14}}{4.3\times 10^{-10}}$

$K_a=2.3\times 10^{-5}$

Hence, the correct answer is option (A).