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Question

What is the pH of the solution when 0.2 mole of hydrochloric acid is added to one litre of a solution containing 1 M acetic acid and acetate ion? Assume that the total volume is one litre. Ka for CH3COOH=1.8×105

A
4.58
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B
9.16
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C
7
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D
2.37
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Solution

The correct option is A 4.58
On adding HCl, the free hydrogen ions
combine with CH3COO ions to form
CH3COOH. Thus, the concentration
of acetic acid increases while that of
CH3 COO ions decreases.

[CH3COOH]=(0.2+1)=1.2 mol litre1
[Salt]=(10.2)=0.8 mol litre1

According to Henderson's equation

pH=log10[Salt][Acid]log ka

=log100.81.2log101.8×105

=log10 2log10 3log10 1.8×105

= 4.5687

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