CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
During an investigation of carbonate chemistry, a student bubbles carbon dioxide gas through pure water until equilibrium is established. The following sequence summarizes two proton-transfer steps that occur in the resulting solution:
Step 1: CO32−(aq)+H3O+(aq)⇌HCO3−(aq)+H2O(l)
Step 2: HCO3−(aq)+H3O+(aq)⇌H2CO3(aq)+H2O(l)
Use these two steps to analyze the acid–base behavior of each species present.
(a) For EACH step, identify the Brønsted–Lowry acid and the Brønsted–Lowry base in the forward direction. Support each identification with a clear description of the proton transfer involved.
(b) For EACH step, write the corresponding conjugate acid or conjugate base that forms as a result of the proton transfer.
(c) The hydronium ion H3O+ acts as an acid in both steps. Using the reactions, compare the relative base strength of CO32− and HCO3−. Justify your comparison with specific reference to the ease or difficulty of the proton-transfer reactions.
(d) Predict whether HCO3− is more likely to act as an acid or as a base when added to pure water. Explain your prediction in terms of the species identified in parts (a) and (b).