Take about 1g solid NaCl in a clean anddry test tube and set up the apparatus asshown in Fig. 2.4.n Add some concentrated sulphuric acid tothe test tube.n What do you observe? Is there a gas comingout of the delivery tube?n Test the gas evolved successively with dryand wet blue litmus paper.n In which case does the litmus paper changecolour?n On the basis of the above Activity, what doyou infer about the acidic character of:(i) dry HCl gas(ii) HCl solution?
Question
Take about 1g solid NaCl in a clean anddry test tube and set up the apparatus asshown in Fig. 2.4.n Add some concentrated sulphuric acid tothe test tube.n What do you observe? Is there a gas comingout of the delivery tube?n Test the gas evolved successively with dryand wet blue litmus paper.n In which case does the litmus paper changecolour?n On the basis of the above Activity, what doyou infer about the acidic character of:(i) dry HCl gas(ii) HCl solution?
Solution
When you add concentrated sulphuric acid to the test tube containing solid NaCl, you will observe a reaction taking place. A gas will start to come out of the delivery tube. This gas is Hydrogen Chloride (HCl).
When you test this gas with dry and wet blue litmus paper, you will notice a change in color in the case of the wet litmus paper. The blue litmus paper will turn red, indicating the presence of an acid. The dry litmus paper, however, will not change color.
Based on this activity, we can infer the following about the acidic character of HCl:
(i) Dry HCl gas: It does not show acidic character because it does not turn blue litmus paper red. This is because for a substance to show its acidic or basic character, it must be in a solution. In the gaseous state, HCl does not ionize into H+ and Cl- ions, which are responsible for the acidic character.
(ii) HCl solution: It shows acidic character because it turns blue litmus paper red. When HCl is in solution, it ionizes into H+ and Cl- ions. The H+ ions interact with water to form hydronium ions (H3O+), which give the solution its acidic properties.
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