The number of moles of \(\mathrm{NH_4Cl}\) that should be added with 1 L of 1M \(\mathrm{NH_4OH}\) for preparing a buffer solution of pH = 9 is [\(K_b = 1.8 \times 10^{-5}\)]

Question and options

The number of moles of

\mathrm{NH_4Cl}

that should be added with 1 L of 1M

\mathrm{NH_4OH}

for preparing a buffer solution of pH = 9 is [

K_b = 1.8 \times 10^{-5}

]

Correct answer: D - 1.8 moles

pOH = 14 - 9 = 5. Henderson:

\mathrm{pOH} = \mathrm{p}K_b + \log([\text{salt}]/[\text{base}])

;

\mathrm{p}K_b = 4.745

, so

\log[\text{salt}] = 0.255

and

[\mathrm{NH_4Cl}] = 1.8

mol in 1 L.