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Question

(i) Draw a labelled diagram and explain the laboratory preparation of hydrogen chloride gas. Give the balanced equations.
(ii) How will you prove that the gas prepared is HCl?
(iii) Name the drying agent used to dry HCl gas.
(iv) How is the gas collected and why?
(v) What are the important precautions?

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Solution

(i) The laboratory arrangement for the preparation of hydrogen chloride is given below:

Reactions at temperature below 2000C involved in the above preparation method is as follows:

NaCl (s) + H2SO4 (aq) → NaHSO4 (s) + HCl (g)
Sodium chloride Sulphuric acid Sodium hydrogen Hydrogen chloride
sulphate gas

(ii) To identify the gas formed in the jar, a glass rod dipped in ammonia solution is brought near the mouth of the jar. Dense white fumes of ammonium chloride are observed. This proves the presence of HCl gas in the jar.

(iii) Hydrogen chloride gas is dried by passing it through concentrated sulphuric acid.

(iv) Hydrogen chloride gas is heavier than air. Therefore, it is collected by the upward displacement of air.

(v) Important precautions that should be taken during the preparation of hydrogen chloride gas are

  1. The lower end of the thistle funnel must be dipped below the concentrated sulphuric acid.
  2. The temperature of the reaction should be maintained at or below 2000C because above this temperature, sodium sulphate forms a hard crust, which sticks to the bottom of the flask, and is difficult to remove.

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