Science (086) — AI-generated practice question

The stomach produces hydrochloric acid (HCl) for digestion. During excess acid production, the pH of the stomach falls too low, causing pain and irritation.

Milk of magnesia is magnesium hydroxide — Mg(OH)₂ — a mild base. When taken, it neutralises the excess hydrochloric acid in the stomach:

$$\text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O}$$

This neutralisation reaction raises the stomach's pH back to a comfortable level, relieving pain. Since Mg(OH)₂ is a mild base, it does not make the stomach too alkaline, making it a safe antacid.

Source: Acids, Bases and Salts (Chapter 2), Section 2.3.1 — pH in our digestive system

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• 3 marks = 3 key points: (1) stomach produces excess HCl → low pH, (2) Mg(OH)₂ is a mild base/antacid, (3) neutralisation reaction raises pH and relieves pain.
• Always write the balanced equation — examiners expect it and it can fetch a dedicated mark.
• The word "mild base" is important; it shows you understand why Mg(OH)₂ is safe to use (won't over-alkalise the stomach).
• Directly grounded in the textbook passage: "Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose. These antacids neutralise the excess acid."