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Acids and bases (A-level only)

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Question 56

A mixture of ethanoic acid and sodium ethanoate in aqueous solution acts as an acidic buffer solution.

The equation shows the dissociation of ethanoic acid:

CH3COOH(aq)⇌CH3COO−(aq)+H+(aq) \text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{CH}_3\text{COO}^-\text{(aq)} + \text{H}^+\text{(aq)} CH3​COOH(aq)⇌CH3​COO−(aq)+H+(aq)

Calculate the mass, in g, of sodium ethanoate (CH3COONa\text{CH}_3\text{COONa}CH3​COONa) that must be added to 50.0 cm350.0\text{ cm}^350.0 cm3 of 0.200 mol dm−30.200\text{ mol dm}^{-3}0.200 mol dm−3 ethanoic acid to produce a buffer solution with pH=4.90\text{pH} = 4.90pH=4.90 at 298 K298\text{ K}298 K.

For ethanoic acid, pKa=4.76\text{p}K_a = 4.76pKa​=4.76 at 298 K298\text{ K}298 K.

Assume that the volume of the solution remains constant.

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Acids and bases (A-level only) Questions

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  3. /Acids and bases (A-level only)