CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A piece of solid zinc oxide, ZnO(s), is added to an excess of concentrated aqueous sodium hydroxide. The following net-ionic equation summarizes the reaction that occurs:
ZnO(s)+2OH−(aq)+H2O(l)→[Zn(OH)4]2−(aq).
Address the tasks below related to this proton-transfer process.
(a) Identify which species acts as the Brønsted–Lowry acid and which acts as the Brønsted–Lowry base in the reaction as written. Explain your reasoning in terms of proton donation and acceptance.
(b) Zinc hydroxide, Zn(OH)2, can precipitate when zinc ions are added to a neutral solution, yet it dissolves in strongly basic solution to form [Zn(OH)4]2−. Using your answer to part (a), explain how the amphoteric nature of Zn(OH)2 accounts for this behavior.
(c) Predict what would happen if solid ZnO were instead added to a strongly acidic solution such as 6 M HCl. Write a balanced net-ionic equation for the dominant reaction and briefly justify the roles of acid and base.