500 mL of a buffer contains 0.50 M NH3 and 0.20 M NH4Cl. On bubbling 0.050 mol of HCl gas (no volume change), the pH becomes (given pK_b = 4.74, pK_w = 14)

JEE Advanced levelSingle correct optionDifficulty 3 of 3ie149

500 mL of a buffer contains 0.50 M $NH X_{3}$ and 0.20 M $NH X_{4} Cl$ . On bubbling 0.050 mol of HCl gas (no volume change), the pH becomes (given $p K_{b} = 4.74$ , $p K_{w} = 14$ )

Initially NH3 = 250 mmol, NH4+ = 100 mmol. HCl (50 mmol) gives NH3 = 200, NH4+ = 150 mmol. pOH =

4.74 + lo g (150/200) = 4.615

; pH = 9.38.

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