Identification of gases

part 3 of 12.5 Identification of ions and gases

Test for ammonia gas: NH​₃

• Ammonia turns damp red litmus paper blue

• Hold the litmus paper near the mouth of the test tube, but be careful to avoid touching the sides of the test tube

Test for carbon dioxide gas: CO₂

• bubble the gas through an aqueous solution of limewater (calcium hydroxide)

• If the gas is carbon dioxide, the limewater turns cloudy white

Test for chlorine gas: Cl₂

• If chlorine gas is present, damp blue litmus paper will turn red and then be bleached white

  • Chlorine should always be handled in a fume cupboard due to its toxicity

Test for hydrogen gas: H₂

• hold a burning splint at the open end of a test tube of gas

• If the gas is hydrogen it burns with a loud “squeaky pop” 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

Test for oxygen gas: O₂

• place a glowing splint inside a test tube of gas

• If the gas is oxygen, the splint will relight

Test for sulfur dioxide gas: SO₂

• Bubble the gas through an acidified solution of potassium manganate(VII)

• If the gas is sulfur dioxide, the potassium manganate(VII) changes from purple to colourless