RP 04 Identification of cations and anions

• What is the procedure to test for group 2 metal cations?

  Place 10 drops of a group 2 compound in a test tube, add NaOH, and record observations.
• What should you do after adding 10 drops of NaOH to the group 2 compound?

  Continue to add NaOH until it is in excess and record any observations.
• What are the results from the reactions of group 2 metal cations with NaOH?

  • Barium Chloride: No change
  • Calcium Bromide: White precipitate of Ca(OH)2
  • Magnesium Chloride: White precipitate of Mg(OH)2 (slightly white at 10 drops of NaOH)
  • Strontium Chloride: Slight white precipitate (initially colourless)
• How would you distinguish between calcium bromide and strontium chloride?

  By adding BaCl2 and sulfuric acid and observing the results.
• What are the results from the reactions of calcium bromide and strontium chloride with sulfuric acid?

  • Barium Chloride: White precipitate
  • Calcium Bromide: Slight white precipitate
  • Magnesium Chloride: Slight white precipitate
  • Strontium Chloride: White precipitate

  
• What are the overall results for the Group 2 reactions with excess NaOH and H2SO4?

  • Ba2+: No change with NaOH, White precipitate with H2SO4
  • Ca2+: White precipitate with NaOH, Slight white precipitate with H2SO4
  • Mg2+: White precipitate with NaOH, Colourless solution with H2SO4
  • Sr2+: Slight white precipitate with NaOH, White precipitate with H2SO4
• How do you test for ammonium (NH4+) ions?

  By adding NaOH to NH4Cl, warming the solution, and testing the gas with damp red litmus paper.
• What indicates the presence of ammonium ions when testing with litmus paper?

  If the damp red litmus paper turns blue, ammonium ions are present.
• How do you test for group 7/halide ions?

  Add nitric acid and silver nitrate to the compound being tested.
• What are the results from the reactions of halide ions with silver nitrate?

  • Cl-: White precipitate
  • Br-: Cream precipitate
  • I-: Yellow precipitate
• How do you test for hydroxide (OH-) ions?

  By testing a solution with red litmus paper or universal indicator paper.
• What color change indicates the presence of hydroxide ions when using litmus paper?

  Damp red litmus paper turns blue.
• How do you test for carbonate (CO3^2-) ions?

  Add Na2CO3 to dilute HCl and observe the reaction with Ca(OH)2.
• What indicates the presence of carbonate ions in the test with Ca(OH)2?

  If Ca(OH)2 goes cloudy, carbonate ions were present.
• How do you test for sulfate (SO4^2-) ions?

  Add HCl and BaCl2 to the suspected sulfate solution.
• What indicates the presence of sulfate ions in the test with BaCl2?

  A white precipitate of BaSO4 will form if sulfate ions are present.
• What is the order of testing ions to prevent false positives?

  • Carbonate → Sulfate → Halide
  • This order prevents unexpected insoluble precipitates from forming.