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  4. The pH of 0.1 M acetic acid solution is closest to [Dissociation constant of the acid, Ka=1.8 × 10-5 ]

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Q. The pH of $0.1\, M$ acetic acid solution is closest to [Dissociation constant of the acid, $K_{a}=1.8 \times 10^{-5}$ ]

KVPYKVPY 2017Equilibrium

Solution:

Given,
dissociation constant, $K_{a}=18 \times 10^{-5}$
Concentration of $\left[ H ^{+}\right]=0.1\, M$
For dissociation of acetic acid
$CH _{3} COOH \rightleftharpoons CH _{3} COO ^{-}+ H ^{+}$
$H ^{+} =\sqrt{k_{a} c}$
$=\sqrt{1.8 \times 10^{-5} \times 0.1}$
$=\sqrt{1.8} \times 10^{-3}$
$=1.34 \times 10^{-3}$
$pH =-\log \left[ H ^{+}\right]$
$=-\log \left(1.34 \times 10^{-3}\right)$
$=3-\log 1.34$
$=2.87$