Carbon Dioxide + Chlorine Tests

What is the test for carbon dioxide?

Bubble the gas through limewater, which turns cloudy or milky.

What is limewater?

A solution of calcium hydroxide, Ca(OH)₂.

Why does carbon dioxide turn limewater cloudy?

It produces a white precipitate of calcium carbonate.

What is the word equation for carbon dioxide reacting with limewater?

Carbon dioxide + calcium hydroxide → calcium carbonate + water.

What is the balanced symbol equation?

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O.

What is the test for chlorine gas?

Expose damp blue litmus paper; it turns red and then white.

Why does damp blue litmus paper initially turn red in chlorine?

Chlorine reacts with water to form acidic substances.

Why does the litmus paper then turn white?

Chlorine produces substances with a bleaching effect.

Why must the litmus paper be damp?

Chlorine must react with water for the characteristic colour changes.

What is a common error in the chlorine test?

Saying chlorine turns litmus red only, without mentioning that it bleaches white.

Why must chlorine be handled carefully in practical work?

It is a toxic gas and should only be used under appropriate laboratory safety controls.

What does a white precipitate in limewater indicate?

The presence of carbon dioxide, under the test conditions.