How to test for gases

• What are the four gases tested in the video?

  Chlorine, oxygen, hydrogen, and carbon dioxide
• What is the first step in testing for chlorine gas?


  You need a test tube full of the sample gas that might contain chlorine
• What happens to damp blue litmus paper when chlorine is present?

  The paper turns from blue to white
• Why might the damp blue litmus paper briefly turn red before turning white?

  Chlorine dissolves in the water on the damp paper and forms hydrochloric acid, which is acidic
• What safety precaution should be taken when testing for chlorine?

  Wear a mask or do it in a fume cupboard
• What is used to test for oxygen gas?

  A glowing splint
• What happens to a glowing splint when it is placed in oxygen?

  The glowing splint will relight
• What is the reaction that occurs when hydrogen gas is tested with a lit splint?

  A squeaky pop is heard as hydrogen burns with oxygen to form water
• What is the test for carbon dioxide gas?

  Bubbling the gas through an aqueous solution of calcium hydroxide
• What happens to lime water when carbon dioxide is bubbled through it?

  The solution goes cloudy
• Why does lime water go cloudy when carbon dioxide is present?

  Calcium carbonate is formed, which is a solid that makes the solution appear cloudy
• What are the results of the tests for the four gases?

  • Chlorine: Turns damp blue litmus paper white
  • Oxygen: Relights a glowing splint
  • Hydrogen: Produces a squeaky pop with a lit splint
  • Carbon dioxide: Causes lime water to go cloudy