CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Citric acid, H3C6H5O7(aq), is a triprotic acid. In aqueous solution at 25 °C it is reacted with a strong base, OH−(aq), supplied from sodium hydroxide.
Complete the tasks below concerning the sequential proton-transfer steps.
(a) Write balanced net-ionic equations for each of the three successive proton-transfer reactions that citric acid can undergo with OH−. Clearly indicate the species present after each deprotonation.
(b) For the net-ionic equation written for the second deprotonation step, label the conjugate acid–base pairs.
(c) Explain, in terms of structure and charge distribution, why the third deprotonation step of citric acid is less favorable than the first.