Science (086) — AI-generated practice question

(a) Chemical Properties of Metals:

(i) Reaction with Oxygen:
Almost all metals react with oxygen to form metal oxides (basic in nature).
$$2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$$

(ii) Reaction with Water:
Metals react with water to form metal oxide/hydroxide and hydrogen gas. Reactivity varies — Na/K react with cold water, Mg with hot water, Al/Fe/Zn with steam; Cu does not react.
$$2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2\uparrow$$

(iii) Reaction with Dilute Acids:
Metals above hydrogen in the activity series react with dilute acids to give salt and hydrogen gas.
$$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\uparrow$$

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(b) HNO₃ is a strong oxidising agent. It oxidises the H₂ produced to water and itself gets reduced to nitrogen oxides (NO, NO₂, N₂O). Therefore, hydrogen gas is not evolved when copper (or most metals) react with dilute HNO₃.

However, magnesium is highly reactive. When Mg reacts with very dilute HNO₃, the acid is too weak to oxidise all the H₂ produced, so hydrogen gas is evolved.

Source: Chapter 3, Section 3.2 (Chemical Properties of Metals)

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• Part (a) carries ~3 marks — one point + equation per reaction type. Keep equations balanced; examiners check this.
• Part (b) carries ~2 marks — the key phrase is "strong oxidising agent" for HNO₃, and "very dilute" for Mg's exception. Both must be stated.
• Common mistake: writing H₂ evolved for Cu + HNO₃ — it is NOT.
• The amphoteric oxide point (Al₂O₃, ZnO) is relevant for oxygen reactions but not required here unless asked specifically.