Two carbonate buffer solutions are prepared at

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

25\,^{\circ}\text{C}

. • Buffer X contains

[\text{HCO}_3^-]=0.20\,\text{M}

and

[\text{CO}_3^{2-}]=0.40\,\text{M}

(total buffer component concentration

0.60\,\text{M}

). • Buffer Y contains

[\text{HCO}_3^-]=0.40\,\text{M}

and

[\text{CO}_3^{2-}]=0.20\,\text{M}

(total buffer component concentration

0.60\,\text{M}

). A third solution, Buffer Z, is prepared with the same component ratio as Buffer X but with every concentration doubled. No numerical

K_a

values are provided; assume typical carbonate equilibria. (a) Without performing numerical calculations, predict which of Buffers X and Y will better resist a sudden addition of

\text{HCl}(aq)

and which will better resist an equal-magnitude addition of

\text{NaOH}(aq)

. Clearly explain the reasoning behind each prediction. (b) Compare the expected buffer capacities of Buffers X and Z toward both acid and base stress. In your explanation, discuss the separate roles played by total component concentration and by the component ratio.

Related theory

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