The tests for: Gases Cations (flame and using sodium hydroxide)

• How is carbon dioxide tested for?

  Bubble it through limewater
• What is the positive result for presence of carbon dioxide?

  Limewater turns cloudy
• How is chlorine tested for?


  Use litmus paper
• What is the positive result for the presence of chlorine?

  Litmus paper is bleached (turns white)
• How is hydrogen tested for?

  Burning splint is held at the open end of a test tube
• What is the positive result for presence of hydrogen?

  A squeaky pop
• How is oxygen gas tested for?

  Glowing splint inserted into a test tube
• What is a positive result for the presence of oxygen?

  Glowing splint re-ignited
• How are flame tests carried out?

  Use safety glasses, clean wire with hydrochloric acid, burn loop in flame, dip wire in substance to be tested, burn in blue flame to observe colour
• What are flame tests used to identify?

  Metal ions (cations)
• What is a positive flame test for lithium?

  Crimson flame
• What is a positive flame test for sodium?

  Yellow flame
• What is a positive flame test for potassium? (

  Lilac flame
• What is a positive flame test for calcium?

  Orange-red flame
• What is a positive flame test for copper?

  Green flame
• How is sodium hydroxide used to identify metal ions in a solution?

  Add sodium hydroxide and observe of precipitate formed
• What is a precipitate?

  An insoluble solid produced in a reaction
• What colour precipitate is observed when sodium hydroxide is added to a solution containing aluminium ions?

  White
• What colour precipitate is observed when sodium hydroxide is added to a solution containing calcium ions?

  White
• What colour precipitate is observed when sodium hydroxide is added to a solution containing magnesium ions?

  White
• What colour precipitate is observed when sodium hydroxide is added to a solution containing copper (II) ions?

  Blue
• What colour precipitate is observed when sodium hydroxide is added to a solution containing iron (II) ions?

  Green
• What colour precipitate is observed when sodium hydroxide is added to a solution containing iron (III) ions?

  Brown
• How are magnesium, calcium and aluminium precipitates distinguished apart?

  Aluminium re-dissolves with excess sodium hydroxide, calcium and magnesium should be flame tested