50 mL of 0.30 M NH4Cl is mixed with 30 mL of 0.20 M NaOH. Given pK_b(NH3) = 4.74, log 2 = 0.301 and log 3 = 0.477, the pH of the mixture is

JEE Advanced levelSingle correct optionDifficulty 3 of 3ia214

$50 mL$ of $0.30 M$ $NH X_{4} Cl$ is mixed with $30 mL$ of $0.20 M$ $NaOH$ . Given $p K_{b} (NH X_{3}) = 4.74$ , $lo g 2 = 0.301$ and $lo g 3 = 0.477$ , the pH of the mixture is

NH X_{4} X^{+}

15 mmol

;

OH X^{-}

6 mmol

, so

NH X_{3} = 6

and

NH X_{4} X^{+} = 9 mmol

remain.

pOH = p K_{b} + lo g (9/6) = 4.74 + 0.176 = 4.916

, so

pH = 9.08

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