Why does dry hydrogen chloride gas not affect dry litmus paper?
Answer and explanation
Correct answer: Water is needed to form ions
The governing concept is that acidic behaviour requires ions in an aqueous medium. Hydrogen chloride molecules do not release mobile hydrogen ions merely because they are present as dry gas; in water they ionise, represented as HCl + H2O → H3O+ + Cl−. Dry litmus therefore shows no acidic colour change. Option A is correct. Litmus can respond to acids as well as bases, HCl is not basic, and the important missing condition is water rather than total chemical inactivity of litmus.
Frequently asked questions
What is the correct answer to this question?
Water is needed to form ions
Why is this the correct answer?
The governing concept is that acidic behaviour requires ions in an aqueous medium. Hydrogen chloride molecules do not release mobile hydrogen ions merely because they are present as dry gas; in water they ionise, represented as HCl + H2O → H3O+ + Cl−. Dry litmus therefore shows no acidic colour change. Option A is correct. Litmus can respond to acids as well as bases, HCl is not basic, and the important missing condition is water rather than total chemical inactivity of litmus.
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.
