8.3 - Identification of ions

• Fill in the blanks for the flame test:

  A) nichrome wire

  B) hydrochloric acid

  C) flame

  D) heat

  
• What is the test for carbonate ions?

  Add dilute acid to a test tube containing the unknown substance and connect it to another test tube containing limewater. Allow the gas produced by the bubbles to travel into the limewater. If the limewater turns cloudy, carbonate ions are present.
• What is the test for halide ions?

  Add dilute nitric acid, followed by silver nitrate solution. If the precipitate is white, chloride is present. Cream is bromide and yellow is iodide. Do not use hydrochloric acid, as it contains chloride ions.
• What is the test for sulphate ions?

  Add dilute hydrochloric acid, followed by barium chloride solution. A white precipitate of barium sulphate means sulphide ions were present.

  • hydrochloric acid is added to remove any carbonate ions that might've been present.
• Should you practise half equations for these ractions?

  Yes - go practise them NOW!!!

  
• How does flame emission spectroscopy work?

  Sample is placed on a flame and ions heat up so electrons jump energy levels. When they drip back to their original energy levels - they emit light. That light passes through a spectroscope, detecting different wavelengths of light. It produces a line spectrum .

  The combination of wavelengths emitted by an ion depends on its charge and electron arrangement .

  
• Advantages of using machines:

  • Very sensitive - they can detect even the smallest amounts of something
  • Very fast - tests can be automated which speeds up the process
  • Very accurate
• What is the flame colour for iodine?

  crimson
• What is the flame colour for sodium?

  yellow
• What is the flame colour for potassium?

  lilac
• What is the flame colour for calcium?

  orange/red
• What is the flame colour for copper?

  green
• What colour is the precipitate for calcium?

  white
• What is the precipitate colour for aluminium?

  white, excess NaOH makes it colourless
• What is the precipitate colour for magnesium?

  white
• What is the precipitate colour for copper (II)?

  blue
• What is the precipitate colour for iron (II)?

  green
• What is the precipitate colour for iron (II)?

  brown