tests

• What is an ion?

  A charged atom, molecule or particle.
• Why must a test for a specific ion be unique?

  To ensure the test gives an easily observed result specific to the ion present.
• Describe how to carry out a flame test to test for ions.

  • Clean a nichrome wire using hydrochloric acid.
  • Turn the Bunsen burner onto the blue flame.
  • Dip the wire in the solution of the substance being tested.
  • Place the wire in the flame and record the colour.
• What is the result of the flame test on lithium ions?

  Crimson flame.
• What is the result of the flame test on sodium ions?

  Yellow flame.
• What is the result of the flame test on potassium ions?

  Lilac flame.
• What is the result of the flame test on calcium ions?

  Orange-red flame.
• What is the result of the flame test on copper ions?

  Blue-green flame.
• Why must the wire be cleaned before carrying out a flame test?

  To remove any unwanted ions that might obscure the colour of the flame.
• Why can a flame test not be used when a compound contains a mixture of metal ions?

  The flame colours will blend together, preventing individual identification.
• What is a precipitate?

  An insoluble solid suspended in a liquid.
• How can you test for aqueous metal ions without using the flame test?

  Add sodium hydroxide solution and observe the colour of the precipitate.
• What colour precipitate forms when sodium hydroxide reacts with calcium ions?

  White.
• What colour precipitate forms when sodium hydroxide reacts with copper(II) ions?

  Blue.
• What colour precipitate forms when sodium hydroxide reacts with iron(II) ions?

  Green.
• What colour precipitate forms when sodium hydroxide reacts with iron(III) ions?

  Brown.
• What colour precipitate forms when sodium hydroxide reacts with aluminium ions?

  White (initially), re-dissolves to form a colourless solution with excess NaOH.
• how do you test for ammonium ions

  Add sodium hydroxide solution to the test substance and gently heat it , if ammonium is present , a pungent smelling gas (ammonia) will be given off , turning damp red litmus paper blue
• How could you distinguish between two solutions containing aluminium ions and calcium ions?

  • Add excess sodium hydroxide.
  • Both will form white precipitates initially.
  • The precipitate from aluminium ions will re-dissolve to form a colourless solution.