The Ion Tests

• Describe the test for group 2 metal ions.

  • Add around 10 drops of 0.1moldm-3 BaCl2 solution
  • Add 10 drops of NaOH or H2SO4 solution and swirl
  • Continue to add NaOH until it is in excess
  • Observe results
• What is the result for the test for Mg2+ with NaOH

  White precipitate --> Mg(OH)2
• What is the expected result when testing for Ca2+ with NaOH?

  White precipitate --> Ca(OH)2
• What is the expected result when testing for Sr+2 with NaOH?

  Slight white precipitate --> Sr(OH)2
• What is the expected result when testing for Ba2+ with excess NaOH?


  No precipitate
• What is the expected result when testing for Mg2+ with H2SO4?

  Colourless solution
• What is the expected result when testing for Ca2+ with excess H2SO4?

  Slight white precipitate --> CaSO4
• What is the expected result when testing for Sr2+ with excess H2SO4?

  White precipitate SrSO4
• What is the expected result when testing for Ba2+ with excess sulfuric acid?

  White precipitate BaSO4
• What is the expected result when testing for Mg2+ with NaOH

  
  

  
  

  
  

  
  

  
  

  White precipitate Mg(OH)2
• What is the expected result when testing for any of the other group 2 metal ions than Mg2+ with ammonia?

  No precipitate is formed
• Describe how we test for ammonium ions.

  • Put ammonium solution in test tube
  • Add about ten drops of NaOH and swirl to ensure contents are mixed well
  • Set up a water bath with a bunsen burner and a beaker of water and put the test tube in it
  • Use a pair of tongs to hold damp red litmus paper over the test tube as fumes are being produced
  • Damp red litmus paper will turn blue in the presence of ammonium gas
• Describe the test for halide ions.

  • Place solution being tested in a test tube
  • Add nitric acid to remove any carbonate impurities
  • Add a few drops of silver nitrate
• What is the expected result when testing for chloride ions?

  A white precipitate will form --> AgCl
• What is the expected result when testing for bromide ions?

  Cream precipitate --> AgBr
• What is the expected result when testing for iodide ions?

  Yellow precipitate --> AgI
• What further tests can we do after testing halide ions with silver nitrate to distinguish between the results? What are the expected results?

  Test with ammonia solution:

  • AgCl forms a soluble complex with dilute ammonia
  • AgBr forms a soluble complex with concentrated ammonia
  • AgI doesn't form a soluble complex with ammonia
• Describe the test for hydroxide ions.

  • Add a small amount of solution to a test tube using a pipette
  • Test the pH of the solution with red litmus paper
  • Red litmus paper will turn blue in the presence of OH-
• How do we test for carbonate ions?

  • Add a small amount of HCl to a test tube
  • Add an equal amount of NaCO3 solution to the test tube
  • Upon adding the sodium carbonate solution, add a bung with a delivery tube to the test tube that leads to a test tube containing limewater
  • Carbon dioxide will turn limewater cloudy
• Describe how we test for sulfate ions.

  • Acidify the sample with dilute hydrochloric acid and add a few drops of aqueous barium chloride
  • White precipitate of BaSO4 will form
• Describe how we carry out a flame test.

  • Clean a platinum wire by dipping it in concentrated hydrochloric acid and hold it into a bunsen flame
  • When clean, moisten it again and dip it into the metal sample and put it back into the flame
• What colour does Li+ burn with?

  Red
• What colour does Na+ burn with?

  Yellow-orange
• What colour does Ca2+ burn with?

  Orange-red
• What colour does Sr2+ burn with?


  Red
• What colour does Ba2+burn with?


  Pale green
• How do we test for carboxylic acids?

  Add sodium hydrogen carbonate, fizzing occurs, gas given off turns limewater cloudy
• How can we test for AlCl3 and MgCl2?

  Add NaOH in excess, AlCl3 precipitate will dissolve and MgCl2 precipitate will not