100 mL of a buffer contains 0.20 M CH3COOH and 0.40 M CH3COONa (pK_a = 4.74). On adding 10 mL of 1.0 M HCl the pH becomes

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JEE Advanced levelSingle correct optionDifficulty 3 of 3ie144

100 mL of a buffer contains 0.20 M $CH X_{3} COOH$ and 0.40 M $CH X_{3} COONa$ ( $p K_{a} = 4.74$ ). On adding 10 mL of 1.0 M HCl the pH becomes

A4.74
B5.04
C4.44
D5.22

Answer: A

Moles: acid = 20 mmol, acetate = 40 mmol. HCl (10 mmol) converts acetate to acid: acid = 30 mmol, acetate = 30 mmol. The ratio is 1 (volume cancels), so pH =

p K_{a}

= 4.74.

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100 mL of a buffer contains 0.20 M CHX3​COOH and 0.40 M CHX3​COONa (pKa​=4.74). On adding 10 mL of 1.0 M HCl the pH becomes

Answer: A

More questions on Buffer solutions and Henderson equation

100 mL of a buffer contains 0.20 M $CH X_{3} COOH$ and 0.40 M $CH X_{3} COONa$ ( $p K_{a} = 4.74$ ). On adding 10 mL of 1.0 M HCl the pH becomes