Dry hydrogen chloride gas does not turn blue litmus red, but it does so after dissolving in water. What does this prove?
Answer and explanation
Correct answer: Formation of ions in water is necessary to show acidic character
The Arrhenius concept explains the observation: an acid produces hydrogen-related ions in aqueous solution. Dry HCl gas has no water medium in which HCl can ionise, so it does not supply hydrogen ions to the litmus and does not show the colour change. In water, HCl ionises essentially completely, producing H₃O⁺ ions, which turn blue litmus red. Therefore, A is correct; the other choices reverse or deny the observation.
Frequently asked questions
What is the correct answer to this question?
Formation of ions in water is necessary to show acidic character
Why is this the correct answer?
The Arrhenius concept explains the observation: an acid produces hydrogen-related ions in aqueous solution. Dry HCl gas has no water medium in which HCl can ionise, so it does not supply hydrogen ions to the litmus and does not show the colour change. In water, HCl ionises essentially completely, producing H₃O⁺ ions, which turn blue litmus red. Therefore, A is correct; the other choices reverse or deny the observation.
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.
