Preparation of HCl gas in Acids, Bases and Salts – Class 10 Science Experiment

Chapter Name: Acids, Bases and Salts

Activity Name: Preparation of HCl gas in Acids, Bases and Salts

Activity Description:

This experiment involves the preparation of hydrogen chloride (HCl) gas by reacting solid sodium chloride (NaCl) with concentrated sulfuric acid (H2SO4) in a test tube. The gas evolved is then tested with dry and wet blue litmus paper to observe its acidic properties. The HCl gas is also shown to dissociate in water to form hydronium ions (H3O+).

Required Items:

1. Solid sodium chloride (NaCl)
2. Concentrated sulfuric acid (H2SO4)
3. Test tube
4. Delivery tube
5. Dry and wet blue litmus paper
6. Guard tube (containing calcium chloride) – optional, for humid climates

Step by Step Procedure:

1. Take about 1.0g of solid NaCl and place it in a clean and dry test tube.
2. Add some concentrated sulfuric acid to the test tube containing NaCl.
3. Observe the reaction and check if there is a gas coming out of the delivery tube.
4. Test the gas evolved with dry and wet blue litmus paper separately.
5. Note the changes in the color of the litmus paper.
6. If required, pass the gas through a guard tube containing calcium chloride to dry the gas.
7. Write the chemical equation for the reaction taking place at the mouth of the delivery tube.

Experiment Observations:

• Gas evolved during the reaction (HCl gas).
• Dry litmus paper: No change in color.
• Wet blue litmus paper: Turns red.

Precautions:

1. Handle concentrated sulfuric acid with care as it is corrosive.
2. Perform the experiment in a well-ventilated area or under a fume hood.
3. Use dry and wet blue litmus paper separately to test the gas.
4. In humid climates, use a guard tube with calcium chloride to dry the gas.

Lesson Learnt from Experiment:

Dry HCl gas (hydrogen chloride) does not show acidic properties since it does not change the color of dry litmus paper. However, when HCl gas dissolves in water, it forms hydronium ions (H3O+) and exhibits acidic behavior, turning wet blue litmus paper red.