A student passes dry hydrogen chloride gas separately over dry and moist blue indicator papers. Only the moist paper turns red. Which principle is proved?
Answer and explanation
Correct answer: Acidic properties appear when ions form in the presence of water.
The experiment demonstrates the role of water in producing acidic ions. Dry hydrogen chloride gas does not provide mobile H⁺ or hydronium ions to the dry indicator, so no red colour appears. On moist paper, HCl dissolves in water and ionises, forming hydronium ions; these give the acidic indicator colour. Therefore A is correct. The result does not show that HCl is basic, that dry paper is defective, or that water alone is an acid.
Frequently asked questions
What is the correct answer to this question?
Acidic properties appear when ions form in the presence of water.
Why is this the correct answer?
The experiment demonstrates the role of water in producing acidic ions. Dry hydrogen chloride gas does not provide mobile H⁺ or hydronium ions to the dry indicator, so no red colour appears. On moist paper, HCl dissolves in water and ionises, forming hydronium ions; these give the acidic indicator colour. Therefore A is correct. The result does not show that HCl is basic, that dry paper is defective, or that water alone is an acid.
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
