Question

The $ p{{K}_{b}} $ value of $ N{{H}_{3}} $ is 5. Calculate the $ pH $ of the buffer solution, $ 1\,\,L $ of which contains $ 0.01\,\,M\,\,N{{H}_{4}}Cl $ and $ 0.10\,\,M\,\,N{{H}_{4}}OH $ :

• A. 4
• B. 6
• C. 8
• D. 10

Answer 1

Answer: (D)

$pOH = p K_{b}+\log \frac{[\text { salt }]}{[\text { base }]}$
Given : $pK _{b}=5$, [base $]=0.10 M$,
[salt] $=0.01 M$
$\therefore pOH =5+\log \frac{0.01}{0.10}=4$
$ pH + pOH =14 $
$\therefore pH =14-4 =10 $