40 mL of 0.20 M NH3 is mixed with 30 mL of 0.10 M HCl. Given pK_b(NH3) = 4.74 and log 2 = 0.301, log 3 = 0.477, the pH is

JEE Main levelSingle correct optionDifficulty 2 of 3ia192

$40 mL$ of $0.20 M$ $NH X_{3}$ is mixed with $30 mL$ of $0.10 M$ $HCl$ . Given $p K_{b} (NH X_{3}) = 4.74$ and $lo g 2 = 0.301$ , $lo g 3 = 0.477$ , the pH is

NH X_{3}

8 mmol

;

HCl

3 mmol

. After reaction

NH X_{3} = 5

and

NH X_{4} X^{+} = 3 mmol

pOH = p K_{b} + lo g (3/5) = 4.74 - 0.222 = 4.518

, so

pH = 9.48

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