Two aqueous buffers are prepared at 25 ,°C using acetic acid ( , ) and sodium acetate
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Two aqueous buffers are prepared at 25\,°C using acetic acid (HC2H3O2, Ka=1.8×10−5) and sodium acetate.
• Buffer P is 0.10\,M in HC2H3O2 and 0.10\,M in C2H3O2−.
• Buffer Q is 0.50\,M in HC2H3O2 and 0.50\,M in C2H3O2−.
The initial pH of the two buffers is identical.
Answer the following questions about their ability to oppose pH change.
(a) State a concise definition of buffer capacity in the context of acid–base equilibria.
(b) Without performing numerical calculations, identify which buffer (P or Q) can neutralize a larger amount of 0.10 M NaOH before its pH rises by 1.0 unit, and justify your choice in terms of chemical species present.
(c) Both buffers are diluted by adding an equal volume of distilled water to each sample. Explain how the dilution affects the absolute buffer capacity of P and Q, and indicate whether the relative ordering you stated in part (b) changes after dilution.
(d) The temperature of each diluted buffer is then increased by 20 °C. Assume the percent change in Ka for acetic acid is the same in both solutions. Predict whether this temperature change alters the comparison of the two buffers’ capacities, and justify your answer.