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Question

What is the pH of the solution when 0.2 mole of HCl is added to one litre of a solution containing 0.1 M each of CH3COOH and acetate ion?
[Assume that the volume is 1 litre, Ka=1.8×105 ]

A
pH=1
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B
pH=2
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C
pH=4.57
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D
None of the above
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Solution

The correct option is A pH=1
CH3COO+HClCH3COOH+ClInitial moles0.10.200Moles after reaction00.10.10.1
Total moles of CH3COOH=0.1+0.1=0.2
Since CH3COOH is weak acid and HCl is stong acid. In solution, both strong acid (HCl) and weak acid (CH3COOH) are present, therefore the dissociation of CH3COOH is suppressed by the strong acid (HCl), due to common ion effect.

So, here we can neglect the H+ ion concentration from the CH3COOH. We can consider the conc. of H+ from the strong acid HCl only.

[HCl]=[H+]=0.1
pH=log[H+]=log(0.1)=1

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