Question

Class XII students were asked to prepare one litre of buffer solution of pH $8.26$ by their Chemistry teacher. The amount of ammonium chloride to be dissolved by the student in $0.2$ M ammonia solution to make one litre of the buffer is (Given : $pK_b$ $(NH_3)$ = $4.74$, Molar mass of $NH_3$ = $17$ g $mol^{–1}$, Molar mass of $NH_4Cl$ = $53.5$ $g$ $mol^{–1}$)

• A. 53.5 g
• B. 72.3 g
• C. 107.0 g
• D. 126.0 g

Answer 1

Answer: (C)

107.0 g

Answer 2

For basic Buffer,

$pOH=pK_b+log\frac{[salt]}{[Base]}$

$pOH=14–8.26=5.74$

$5.74=4.74+log\frac{[NH_4Cl]}{0.2}$

$[NH_4Cl]=2 M$

Moles of $NH_4Cl = 2 × 1 = 2$ $moles$

Weight of $NH_4Cl$ = $2 × 53.5 = 107$ $g$