Science — AI-generated practice question

Fizzing will occur more vigorously in the test tube containing HCl (hydrochloric acid).

Reaction:
$$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\uparrow$$
$$\text{Mg} + 2\text{CH}_3\text{COOH} \rightarrow \text{(CH}_3\text{COO)}_2\text{Mg} + \text{H}_2\uparrow$$

Reason: HCl is a strong acid and completely dissociates in water, producing a higher concentration of H⁺ ions. CH₃COOH is a weak acid and partially dissociates, producing fewer H⁺ ions. Since the rate of reaction with magnesium depends on the concentration of H⁺ ions, more hydrogen gas is evolved per unit time with HCl, causing more vigorous fizzing.

Source: Chapter 2 (Acids, Bases and Salts), Exercise Q.10

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• Key concept: strong acid vs. weak acid — same molar concentration but different degree of ionisation.
• HCl → fully ionised; CH₃COOH → partially ionised. More H⁺ = faster reaction = more vigorous fizzing.
• Examiners expect you to name the type of acid (strong/weak), link it to H⁺ ion concentration, and connect that to the rate of reaction. Writing the balanced equations earns extra marks and shows conceptual clarity.