66. Testing for Gases

1. Chlorine (Cl2)

• The Test: Use a piece of damp blue litmus paper.

• The Result: The litmus paper will be bleached and turn white.

• Note: The paper may briefly turn red before turning white because chlorine reacts with the water on the paper to form hydrochloric acid.

• Safety: Chlorine is poisonous; this should be done in a fume cupboard.

2. Oxygen (O2)

• The Test: Use a glowing splint (one that has been blown out but is still glowing red).

• The Result: The glowing splint will relight.

3. Hydrogen (H2)

• The Test: Use a burning splint.

• The Result: You will hear a distinctive "squeaky pop" sound. This is caused by the hydrogen burning rapidly with oxygen in the air to form water.

4. Carbon Dioxide (CO2)

• The Test: Bubble the gas through an aqueous solution of calcium hydroxide, commonly known as limewater.

• The Result: The limewater will turn cloudy (or milky).

• Science: This happens because the CO2 reacts with the calcium hydroxide to form calcium carbonate (CaCO3), which is an insoluble white solid.

Summary Table