Overview
This lecture covers the standard laboratory tests used to identify four common gases: chlorine, oxygen, hydrogen, and carbon dioxide.
Test for Chlorine
- Place a damp blue litmus paper into a test tube containing the gas sample.
- Chlorine turns blue litmus paper white due to its bleaching effect.
- The paper may briefly turn red before white because chlorine forms hydrochloric acid.
- Chlorine is poisonous, so use a fume cupboard or wear a mask.
Test for Oxygen
- Insert a glowing (not flaming) splint into the gas sample.
- Oxygen will relight a glowing splint, indicating its presence.
Test for Hydrogen
- Place a lit splint near the mouth of a test tube containing hydrogen.
- Hydrogen produces a squeaky pop sound as it burns with oxygen to form water.
Test for Carbon Dioxide
- Bubble the gas through an aqueous solution of calcium hydroxide (limewater).
- Carbon dioxide turns limewater cloudy by forming solid calcium carbonate particles.
Key Terms & Definitions
- Litmus paper — chemically treated paper used to test for acidity or alkalinity.
- Glowing splint — a wooden splint with a red-hot end but no flame.
- Calcium hydroxide (limewater) — a clear solution used to detect carbon dioxide by turning cloudy.
- Calcium carbonate — a white, insoluble solid formed when carbon dioxide reacts with limewater.
Action Items / Next Steps
- Review the summarized gas tests and practice identifying gases using these methods.