100cm3 buffer solution of 0.1M CH3COOH and 0.05M CH3COONa are added 3cm3 HCl 0.01M. Ph =?

Question

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Answer 1

100 cm³ buffer solution of 0.1M CH₃COOH and 0.05M CH₃COONa contains 10 mmol of acetic acid and 5 mmol of acetate

3 cm³ HCl 0.01M contain 0.03 mmol HCl

When 0.03 mmol HCl are added to the buffer solution it will convert acetate to acetic acid. The new amount of acetate is now 4.97 mmol and the new amount of acetic acid is now 10.03 mmol

Then we can find pH of the mixture using the Henderson-Hasselbalch equation, and the pKa of acetic acid (4.75)

pH = pKa + log [Salt] / [Acid] = 4.75 + log (4.97/10.03) = 4.45