Science (086) — AI-generated practice question

Zinc reacts with dilute H₂SO₄ as well as NaOH solution to produce hydrogen gas, which shows that zinc is amphoteric in nature — it behaves as a metal (reacting with acid) and also as a non-metal (reacting with base).

With dilute H₂SO₄:
$$\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\uparrow$$
The salt formed is zinc sulphate, containing the simple $\text{SO}_4^{2-}$ anion from the acid.

With NaOH:
$$\text{Zn} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2\uparrow$$
The salt formed is sodium zincate, which contains the oxyanion $\text{ZnO}_2^{2-}$ — a negative ion composed of the metal and oxygen.

This difference arises because when a base reacts with a metal, the salt formed has a negative ion composed of the metal and oxygen (an oxyanion), whereas an acid simply donates its own anion ($\text{SO}_4^{2-}$) to the salt.

Source: Chapter 2 (Acids, Bases and Salts), What you have learnt; Chapter 3 (Metals and Non-metals), What you have learnt

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• Key concept tested: Amphoteric nature of zinc — it reacts with both acids and bases. The textbook explicitly states that zinc oxide is an amphoteric oxide, implying zinc itself is amphoteric.
• Oxyanion point: The "What you have learnt" summary in Chapter 2 directly states: "When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen." Quote or paraphrase this for full marks.
• Do not confuse ZnSO₄ (sulphate anion comes from the acid, not from zinc) with Na₂ZnO₂ (zincate anion is built from zinc + oxygen — hence the oxyanion).
• Write both equations; one equation alone will lose a mark.