A research team is evaluating the buffer capacities of two weak acid/strong base…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A research team is evaluating the buffer capacities of two weak acid/strong base titration systems, System A and System B. Both involve titration of 25.0 mL of a 0.100 M monoprotic weak acid with 0.100 M NaOH. For each system, the team has measured the slope of the pH–volume curve, (dVNaOHdpH), at several points in the buffer region.
Volume NaOH added (mL) | (dVdpH)A | (dVdpH)B
5.0 | 0.12 | 0.05
6.0 | 0.11 | 0.05
7.0 | 0.10 | 0.05
In System A the half-equivalence pH is 4.80, whereas in System B the half-equivalence pH is 3.20.
Answer the following questions about the two systems.
(a) Explain how the reported slope values are related to buffer capacity.
(b) Identify which system exhibits the greater buffer capacity in the region studied, and justify your answer quantitatively using the data provided.
(c) Calculate the ratio [HA][A−] in System A when 6.0 mL of NaOH have been added.
(d) If the goal is to formulate a buffer that resists pH change near 3.0, which system would be more appropriate? Provide chemical reasoning that connects acid strength, pKa, and buffer capacity.