- Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in Fig. 2.4.
- Add some concentrated sulphuric acid to the test tube.
- What do you observe? Is there a gas coming out of the delivery tube?
✅ Answer: HCl gas comes out of the delivery tube.
- Test the gas evolved successively with dry and wet blue litmus paper.
- In which case does the litmus paper change colour?
✅ Answer: When HCl gas is tested with wet blue litmus paper, it becomes red colour. But with dry litmus paper, no colour change occurs.
- On the basis of the above Activity, what do you infer about the acidic character of:
- (i) dry HCl gas
- (ii) HCl solution?
✅ Answer: (i) dry HCl gas cannot produce H+ ions. So it does not behave as an acid.
(ii) HCl solution can produce H+ ions and behave as an acid.
HCl + H2O → H3O+ + Cl–