Question

What is the pH of buffer solution prepared by mixing \[\text{0.2MNH4OHand0.4MNH4Cl}\] solution. \[(\mathrm{pK_{b}~of~NH_{4}OH=4.620})\]

Options

• 4.025

• 7.035

• 9.079

• 8.450

Answer 1

9.079

Explanation:

For a buffer solution,
\[\mathrm{pOH=pK_b+log_{10}\frac{[Salt]}{[Base]}}\]
\[=4.620+\log_{10}\frac{0.4}{0.2}\]
\[=4.620+0.301\]
\[\therefore\quad\mathrm{pOH}=4.921\]
\[\begin{array} {c}\mathrm{Now,~pH+pOH=14} \\ \therefore\quad\mathrm{pH=14-pOH=14-4.921=9.079} \end{array}\]