A litre of buffer solution contains 0 . 1 mole of each of NH 3 and NH 4 Cl . On the addition of 0 . 02 mole of HCl by dissolving gaseous HCl , the pH of the solution is found to be _ _ _ _ _ × 10 - 3

Question

A litre of buffer solution contains 0 . 1 mole of each of NH 3 and NH 4 Cl . On the addition of 0 . 02 mole of HCl by dissolving gaseous HCl , the pH of the solution is found to be _ _ _ _ _ × 10 - 3 (Nearest integer) Given: pK b NH 3 = 4 . 745 log 2 = 0 . 301 log 3 = 0 . 477 T = 298 K ]

TestHub · Accepted Answer

In resultant solution after addition of $HCl$ to the basic buffer:

$n_{{NH}_{3}} = 0.1 - 0.02 = 0.08$

$n_{{NH}_{4} Cl} = n_{{NH}_{4}^{+}} = 0.1 + 0.02 = 0.12$

Using Henderson-Hasselbach equation:

$pOH = {pK}_{b} + \log \frac{[{NH}_{4}^{+}]}{[{NH}_{3}]}$

$= 4.745 + \log \frac{0.12}{0.08}$

$= 4.745 + \log \frac{3}{2}$

$= 4.745 + 0.477 - 0.301$

$pOH = 4.921$
We know,

$pH = 14 - pH$

$= 9.079$

Chemistry - Ionic Equilibrium Question with Solution | TestHub

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