Science — AI-generated practice question

This experiment proves that water is essential for acids to show acidic behaviour. Dry HCl gas does not ionise in the absence of water, so it cannot produce H⁺ ions and does not turn dry litmus red. When water is present (wet litmus), HCl ionises to produce H⁺ (hydronium) ions, turning it red:

$$\text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^-$$

Thus, H⁺ ions are produced by HCl only in the presence of water.

Source: Chapter 2, Section 2.2.1

---

• Examiners expect two key points: (1) dry HCl has no H⁺ ions (no water to ionise it), and (2) water enables ionisation/dissociation to form H₃O⁺.
• Writing the equation earns a mark and shows understanding of the chemistry.
• The core conclusion — "acids show acidic character only in aqueous solution" — must be stated explicitly.