Verified Solution • 2025–26 Session moderate

QJEEM22Chb106: JEE Main 2022 Chemistry - Class 11 JEEM22Chb106 Solution: Class XII students were asked to prepare one litre of buffer…

Class XII students were asked to prepare one litre of buffer solution of pH 8.26\mathrm{pH} \,8.26 by their Chemistry teacher: The amount of ammonium chloride to be dissolved by the student in 0.2 M0.2\, \mathrm{M} ammonia solution to make one litre of the buffer is :

(Given: pKb(NH3)=4.74\mathrm{pK}_{\mathrm{b}}\left(\mathrm{NH}_{3}\right)=4.74

Molar mass of NH3=17 g mol−1\mathrm{NH}_{3}=17 \mathrm{~g} \mathrm{~mol}^{-1}

Molar mass of NH4Cl=53.5 g mol−1\mathrm{NH}_{4} \mathrm{Cl}=53.5 \mathrm{~g} \mathrm{~mol}^{-1} )

Multiple Choice Options

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

Step-by-Step Verified Solution

For basic Buffer, pOH=pKb+log⁡[ salt ][ Base ]\mathrm{pOH}=\mathrm{pK}_{\mathrm{b}}+\log \frac{[\text { salt }]}{[\text { Base }]}

pOH=14−8.26=5.74\mathrm{pOH}=14-8.26=5.74

5.74=4.74+log⁡[NH4Cl]0.25.74=4.74+\log \frac{\left[\mathrm{NH}_{4} \mathrm{Cl}\right]}{0.2}

[NH4Cl]=2M\left[\mathrm{NH}_{4} \mathrm{Cl}\right]=2 \mathrm{M}

Moles of NH4Cl=2×1=2\mathrm{NH}_{4} \mathrm{Cl}=2 \times 1=2 moles

Weight of NH4Cl=2×53.5=107 g\mathrm{NH}_{4} \mathrm{Cl}=2 \times 53.5=107 \mathrm{~g}

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