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Question

The pH of 0.3 M acetic acid (CH3COOH) with Ka=1.8×105 is :
Take log10(2.32)=0.36

A
6.56
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B
2.64
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C
4.86
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D
7.63
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Solution

The correct option is B 2.64
Ka=1.8×105
the dissociation of acetic acid is given by
CH3COOHH++CH3COOInitial: 0.3 0 0At equilibrium: 0.3x x xHere x is the dissociation of CH3COOH at equilibrium

Ka=1.8×105=[CH3COO][H+][CH3COOH]=x×x0.3xSince CH3COOH is a weak acid x<<0.3
0.3x0.3Ka=1.8×105=x20.3 x=2.32×103x=[H+]=2.32×103pH=log10[H+]pH=log10(2.3×103)pH=2.638

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