Question
Solution of $$0.1\,N\,N{H_4}OH$$ and $$0.1\,N\,N{H_4}Cl$$ has $$pH$$ 9.25, then find out $$p{K_b}$$ of $$N{H_4}OH.$$
A.
9.25
B.
4.75
C.
3.75
D.
8.25
Answer :
4.75
Solution :
Solution of $$N{H_4}OH$$ and $$N{H_4}Cl$$ acts as a basic buffer solution. For basic buffer solution
$$\eqalign{
& pOH = p{K_b} + {\text{log}}\frac{{\left[ {{\text{salt}}} \right]}}{{\left[ {{\text{base}}} \right]}} \cr
& POH = 14 - pH \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 14 - 9.25 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4.75 \cr
& 4.75 = p{K_b} + {\text{log}}\frac{{0.1}}{{0.1}} \cr
& p{K_b} = 4.75 \cr} $$