Acids, Bases and Salts | Class 10 | Activity 2.9 with Solution

Activity 2.9  
  • 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

Fig. 2.4


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