Science — AI-generated practice question

(a) When sodium hydroxide reacts with zinc metal, it produces sodium zincate and hydrogen gas. The balanced chemical equation is:

$$2\text{NaOH(aq)} + \text{Zn(s)} \rightarrow \text{Na}_2\text{ZnO}_2\text{(aq)} + \text{H}_2\text{(g)}$$

(b) When zinc reacts with dilute sulphuric acid, it also produces hydrogen gas along with zinc sulphate (a salt):

$$\text{Zn(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{(g)}$$

The key difference is that the reaction with H₂SO₄ is a reaction of zinc with an acid, forming a simple salt (ZnSO₄). The reaction with NaOH is a reaction of zinc with a base, forming a complex salt called sodium zincate (Na₂ZnO₂). Not all metals react with bases; zinc is amphoteric (reacts with both acids and bases).

(c) General summary equation for the reaction of a base with a metal:

$$\text{Base} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas}$$

Source: Chapter 2, Section 2.1.2

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• Part (a) tests recall of the specific equation from Activity 2.4 — write it with state symbols for full marks.
• Part (b) requires a comparison: both produce H₂, but the nature of the other product differs — acid gives a normal salt; base gives a complex salt (zincate). Mentioning "not all metals react with bases" or "zinc is amphoteric" adds value.
• Part (c) is a one-line summary modelled on the acid + metal pattern given in the textbook. Keep it in the exact word-equation format the textbook uses.