Why does dry hydrogen chloride gas not change the colour of dry blue litmus paper?
Answer and explanation
Correct answer: Hydrogen ions are not formed without water
Hydrogen chloride shows acidic behaviour only after dissolving in water. In aqueous solution it ionises, producing hydronium ions: HCl + H₂O → H₃O⁺ + Cl⁻. These ions cause blue litmus to turn red. With both the gas and the litmus paper dry, water is unavailable, so hydronium ions are not produced at the paper surface and no colour change occurs. HCl is not basic, and the absence of chlorine is not the reason.
Frequently asked questions
What is the correct answer to this question?
Hydrogen ions are not formed without water
Why is this the correct answer?
Hydrogen chloride shows acidic behaviour only after dissolving in water. In aqueous solution it ionises, producing hydronium ions: HCl + H₂O → H₃O⁺ + Cl⁻. These ions cause blue litmus to turn red. With both the gas and the litmus paper dry, water is unavailable, so hydronium ions are not produced at the paper surface and no colour change occurs. HCl is not basic, and the absence of chlorine is not the reason.
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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