RP4 tests for ions

• the two chemicals which can be used to test for group 2 metal cations are sodium hydroxide and sulfuric acid
• test for group 2 cations using sodium hydroxide:

  • add 10 drops of sample
  • initially all are colourless
  • add 10 drops of NaOH
  • Mg = slight white ppt, Ca = slight white ppt, Sr = slight white ppt, Ba = colourless
  • add excess NaOH
  • Mg = white ppt, Ca = slight white ppt, Sr = slight white ppt, Ba = colourless
• test for group 2 cations using sulfuric acid:

  • add 10 drops of sample
  • initially all are colourless
  • add 10 drops of H2SO4
  • Mg = slight white ppt, Ca = slight white ppt, Sr = white ppt, Ba = white ppt
  • add excess H2SO4
  • Mg = colourless, Ca = slight white ppt, Sr = white ppt, Ba = white ppt
• the chemicals which can be used to test for ammonium ions are sodium hydroxide and red litmus paper
• test for ammonium ions:

  • add 10 drops of sample
  • add 10 drops of NaOH and shake
  • warm in a water bath
  • test the fumes with damp red litmus paper
  • positive = damp red litmus paper turns blue
• the chemical which can be used to test for hydroxide ions is damp red litmus paper
• test for hydroxide ions:

  • add 20 drops of sample
  • test with damp red litmus paper
  • positive = damp red litmus paper turns blue
• the chemical which can be used to test for ammonia gas is damp red litmus paper
• test for ammonia gas:

  • add 5 drops of sample to filter paper
  • place filter paper inside petri dish
  • place damp red litmus paper on other side of petri dish
  • add lid to petri dish
  • positive = damp red litmus paper turns blue
• the chemicals which can be used to test for carbonate ions are hydrochloric acid and calcium hydroxide
• test for carbonate ions:

  • add 3cm^3 of sample
  • add 3cm^3 of HCl
  • bubble the gas produced through CaCO3 using a delivery tube
  • positive = CaCO3 turns cloudy from colourless
• the chemicals which can be used to test for sulfate ions are hydrochloric acid and barium chloride
• test for sulfate ions:

  • add 20 drops of sample
  • add 20 drops of HCl
  • add 20 drops of BaCl2
  • positive = white ppt
• the chemicals which can be used to test for halide ions in aqueous solution are nitric acid, silver nitrate, dilute ammonia and concentrated ammonia
• test for halide ions in aqueous solution:

  • add 10 drops of sample
  • add 5 drops of HNO3 and shake
  • add 10 drops of AgNO3
  • Cl = white ppt, Br = cream ppt, I = yellow ppt
  • add excess dilute NH3
  • Cl = colourless, Br = cream ppt, I = yellow ppt
  • add excess concentrated NH3
  • Cl = colourless, Br = colourless, I = yellow ppt
• the chemicals which can be used to test for halide ions in solid salts are sulfuric acid and damp blue litmus paper
• test for chloride ions in solid salts:

  • add 1 spatula of salt
  • add 5 drops of H2SO4
  • positive = effervescence, white steamy fumes
  • test gas produced with damp blue litmus paper
  • positive = damp blue litmus paper turns red
• test for bromide ions in solid salts:

  • add 1 spatula of salt
  • add 5 drops of H2SO4
  • positive = effervescence, orange fumes
  • test gas produced with damp blue litmus paper
  • positive = damp blue litmus paper turns red
• damp red litmus paper turns blue when in contact with alkali and stays red when in contact with acid
• damp blue litmus paper turns red when in contact with acid and stays blue when in contact with alkali
• test for iodide ions in solid salts:

  • add 1 spatula of salt
  • add 5 drops of H2SO4
  • positive = effervescence, purple fumes and purple-black solid
  • test gas produced with damp blue litmus paper
  • positive = damp blue litmus paper turns red