5. A solution contains 0.2M NH4OH and 0.2M NH4CI. If 1.0 mL of 0.001 M HCl is added to it. What will be the [OH-] of the resulting solution [Kb = 2x10-5] ?

5. A solution contains 0.2M NH4OH and 0.2M NH4CI. If 1.0 mL of 0.001 M HCl is added to it. What will be the [OH^-] of the resulting solution [Kb = 2x10^-5] ?

A. 2x10^-5

B. 2x10^-3

C. 5x10^-10

D. None of these

SOLUTION

Concentration of NH4OH = 0.2M

Concentration of NH4Cl = 0.2M

Concentration of HC1 = 0.001 M

[Kb = 2x10^-5] 

Applying Henderson Equation

POH = P^Ka + log [salt/base]

POH = 5 - log 2 + log(0.2/0.2)

POH = 5 - log2

[OH^-] =2x10^-5

So, the [OH^-] of the resulting solution is 2x10^-5 (the option (A) is the correct answer).