Dry hydrogen chloride gas is passed over dry blue litmus paper and no colour change occurs. The same gas is passed over moist blue litmus paper and it turns red. What is the reason?
Answer and explanation
Correct answer: Ion formation in water is required for acidic behaviour
Hydrogen chloride shows acidic behaviour only after dissolving in water, where it ionises and produces hydronium ions: HCl + H₂O → H₃O⁺ + Cl⁻. Dry HCl gas cannot supply these aqueous ions to dry litmus, so there is no colour change. Moist litmus provides water and turns red; therefore option A is correct.
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What is the correct answer to this question?
Ion formation in water is required for acidic behaviour
Why is this the correct answer?
Hydrogen chloride shows acidic behaviour only after dissolving in water, where it ionises and produces hydronium ions: HCl + H₂O → H₃O⁺ + Cl⁻. Dry HCl gas cannot supply these aqueous ions to dry litmus, so there is no colour change. Moist litmus provides water and turns red; therefore option A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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