4. Give a chemical test to distinguish between the following pairs of compounds:

(i) Sodium chloride solution and sodium nitrate solution.

(ii) Hydrogen chloride gas and hydrogen sulphide gas.

(iii) Ethene gas and ethane gas

(iv) Calcium nitrate solution and zinc nitrate solution.

(v) Carbon dioxide gas and sulphur dioxide gas

1. In order to distinguish between sodium chloride and sodium nitrate a solution of silver nitrate can be used.

Silver nitrate will react with sodium chloride to form a white precipitate of silver chloride. On the other hand sodium nitrate will not react with silver nitrate.

NaCl + AgNO3 → AgCl + NaNO3

2. HCl gas reacts with water to from HCl acid. On the other hand H2S gas reacts with water and furnish sulfur ions in the solution.

HCl + H2O → H3O+ + Cl-

H2S + 2H2O → 2H3O+ + S2-

3. Ethane and ethene can be distinguished using bromine water. Ethene will decolorize the bromine water. However on the other hand ethane will not. This is because bromine will add on across the double bond of the unsaturated ethene to produce dibromoethane. The Br2 is removed from the water which becomes clear. In the case of ethane this is already saturated , so no reaction occurs - Bromine water remains brown

4. Calcium nitrate and zinc nitrate can be distinguished using sodium hydroxide solution. When sodium hydroxide solution is added to calcium nitrate a white precipitate is formed which is insoluble in the presence of excess of sodium hydroxide. However when sodium hydroxide is added to zinc nitrate the white precipitate formed in soluble in excess of sodium hydroxide.

5. The simplest test will be to pass both the gases through lime water. Carbon dioxide gas will turn lime water milky due to the formation of calcium carbonate. However when sulfur dioxide is passed through lime water it does not turn milky.

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