Question

The Ka of an acid is 1.3 x 10–7. Based on the Ka and its relationship with Kw, what is the value of Kb?

A) 1.3 x 10–21

B) 7.7 x 10–15

C) 1.3 x 10–14

D) 7.7 x 10–8

Answer 1

Ka x Kb = Kw Kw = 1 x 10⁻¹⁴

(1.3 x 10⁻⁷) x Kb = 1 x 10⁻¹⁴

Kb = ( 1 x 10⁻¹⁴ ) / ( 1.3 x 10⁻⁷)

Kb = 7.7 x 10⁻⁸

Answer D

hope this helps!

Answer 2

Ans: D) 7.7*10-8

Dissociation of an acid leads to the formation of respective ions where in the cation is a proton i.e an H+ ion. In general, if HA is a monoprotic weak acid then it would dissociate as follows:

HA ↔ H⁺ + A⁻

The acid dissociation constant Ka is given as:

Ka = [H⁺][A⁻]

Ka is also related to the dissociation constant of water, Kw and the dissociation constant of the base Kb as follows:

`Kw = Ka*Kb\\Kb = (Kw)/(Ka) \\It is given that:\\Ka = 1.3*10^(-7) \\Kw = 1.0*10^(-14) \\Therefore: Kb = (1.0*10^(-14) )/(1.3*10^(-7) ) = 7.7*10^(-8)`