Hydrogen chloride

Hydrogen chloride gas is prepared by the action of concentrated sulphuric acid on any chloride salt.

$H^+_{(l)} + Cl^-_{(s)}$

The gas is commonly prepared in the laboratory by reacting common salt (sodium chloride) with concentrated sulphuric acid using the set-up shown in the figure below.

The figure for preparation of hydrogen chloride.

The gas is passed through concentrated sulphuric acid in order to be dried. Being very soluble with water and very denser than air, hydrogen chloride gas is collected by downward delivery method.

When concentrated sulphuric acid is added to a chloride salt in the test tube a fuming gas (hydrogen chloride) evolved.

$H^+_{(l)} + Cl^-_{(s)} \rightarrow HCl_{(g)}$

When moist blue litmus paper is brought near the mouth of the test tube the paper turns red. This shows that the gas is acidic.

When a stopper with ammonia solution is introduced into the fuming gas, dense white clouds of ammonium chloride are seen to form above the test tube. When the gas is bubbled through silver nitrate solution a white precipitate of silver chloride forms.

The reaction of hydrogen chloride with ammonia and silver nitrate solution are fully described in the chemical properties of the gas.

1. Hydrogen chloride gas forms white dense fumes with ammonia.
2. The gas forms a white precipitate (silver chloride) with silver nitrate solution.

1. Hydrogen chloride gas gives white fumes in moist air.
2. Is a colourless gas with a choking and irritating smell.
3. It is denser than air.
4. It is soluble in water.

• Reaction with ammonia

Hydrogen chloride gas reacts with ammonia gas to form ammonium chloride. Ammonium chloride is a white solid.

$HCl_{(g)} + NH_{3(g)} \rightarrow NH_4Cl_{(s)}$

• Reaction with silver nitrate solution

The gas forms a white precipitate (AgCl) when bubbled through silver nitrate solution. This is due to the formation of silver chloride which is white and insoluble.

$HCl_{(g)} + AgNO_{3(aq)} \rightarrow AgCl_{(s)} + HNO_{3(aq)}$

• Reaction with water

Hydrogen chloride dissolves and dissociates in water. It forms the hydroxonium ion ($H_3O^+$) which is acidic in nature.

$HCl_{(g)} + H_2O_{(l)} \rightarrow H_3O^+_{(aq)} + Cl^-_{(aq)}$

• Reaction with metals

Aqueous hydrogen chloride behaves as an acid. It reacts with metals to form hydrogen gas and salt.

$Mg_{(s)} + 2HCl_{(aq)} \rightarrow MgCl_{2(aq)} + H_{2(g)}$

$Zn_{(s)} + 2HCl_{(aq)} \rightarrow ZnCl_{2(aq)} + H_{2(g)}$

$Ca_{(s)} + 2HCl_{(aq)} \rightarrow CaCl_{2(aq)} + H_{2(g)}$

• Reaction with carbonates

Hydrogen chloride reacts with carbonates to form a chloride salt, carbon dioxide and water.

$CaCO_{3(s)} + 2HCl_{(aq)} \rightarrow CaCl_{2(aq)} + CO_{2(g)} + H_2O_{(l)}$

Being very soluble with water, hydrogen chloride gas is absorbed in water more quickly than it is being generated. The pressure in the tube and flask is lower than the atmospheric pressure and the water in the beaker is sucked into the flask. If an ordinary delivery tube is used. Hence the inverted funnel is used to prevent this suck-back effect. The hydrogen chloride acid.

1. Hydrogen chloride is used to remove rust from metals.
2. It is used to remove calcium carbonate scale from kettles, pipes, taps washing machines, buckets and tiles.
3. It is used in treatment of drinking and sewage water.
4. Hydrochloric acid is used in volumetric analysis to standardize basic solution.
5. It is used in the manufacture of organic compounds such as PVC (polyvinyl chloride), plastics and insecticides.