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| Preparation of Hydrogen Chloride Gas |
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| Hydrogen chloride gas can be prepared by the direct combination of hydrogen gas and chlorine gas in the presence of sunlight. The reaction is explosive in direct sunlight. However, in diffused sunlight the reaction is slow and controllable. In the dark, the reaction hardly takes place. |
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| Hydrogen chloride gas can also be obtained by burning hydrogen in chlorine. |
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| Activity |
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| Introduce a burning jet of hydrogen into a jar of chlorine. Hydrogen continues to burn, forming hydrogen chloride (Fig.5.2). |
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| When concentrated sulphuric acid is heated with metal chlorides, hydrogen chloride gas is liberated. During the heating, sulphuric acid being less volatile, does not vapourize. |
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| In the laboratory, the chloride used is sodium chloride (common salt) since it is the cheapest and the most easily available chloride. The use of sodium chloride results in the formation of two kinds of salts. At a temperature of about 200oC, sodium hydrogen sulphate is formed; whereas at a much higher temperature, sodium sulphate is formed. |
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| The preparation of hydrogen chloride gas by the above method is carried out at the lower temperature of about 200oC, for the following reasons: |
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 Lower the temperature, lesser the wastage of the fuel. |
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Sodium sulphate formed at a higher temperature, forms a crust on the surface of the glass flask, and it is difficult to remove it. |
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Higher the temperature, greater is the risk of breaking the apparatus. |
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| Activity |
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| Sodium chloride is taken in a round bottomed flask, and concentrated sulphuric acid is added to the flask through the thistle funnel. Then the flask is heated. The hydrogen chloride gas formed is collected by the upward displacement of air. To obtain dry hydrogen chloride gas, it is passed through concentrated sulphuric acid to remove the water vapor (Fig.5.3). |
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| To confirm whether the gas jar is being filled with the gas, a wet blue litmus paper is introduced at the mouth of the jar. If the jar is filled with the gas, the litmus paper turns red. |
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| Potassium chloride also behaves in the same way as sodium chloride while producing hydrogen chloride gas. If any other metal chloride is used, the reaction will be as follows: |
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| Phosphorus (V) oxide or quick lime cannot be used as drying agents for drying hydrogen chloride as both react with the acid. |
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