Testing for Common Gases (OCR Gateway GCSE Chemistry: Combined Science)

• The test for carbon dioxide involves bubbling the gas through an aqueous solution of calcium hydroxide (limewater)
• If the gas is carbon dioxide, the limewater turns milky or cloudy

Diagram showing the test for carbon dioxide gas

• The test for hydrogen is often referred to as the 'squeaky pop' test
• The test for hydrogen consists of holding a burning splint held at the open end of a test tube of gas
• If the gas is hydrogen it burns with a loud “pop” sound which is the result of the rapid combustion of hydrogen with oxygen to produce water
• Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn

Diagram showing the test for hydrogen gas

• The test for oxygen consists of placing a glowing splint inside a test tube of gas
• If the gas is oxygen the splint will relight

Diagram showing the test for oxygen gas

• The test for chlorine makes use of litmus paper
• If chlorine gas is present, damp blue litmus paper will be bleached white
• It may turn red briefly before bleaching, as acids are produced when chlorine comes into contact with water
• Chlorine should always be handled in a fume cupboard due to its toxicity