Qualitative analysis

• What are anions also known as?
• Write an equation for the sulfate ion test
• What are the observations for a positive test of carbonate ions, CO3^2-?
• How can you test for a halide ion?
• What do you use to test for halide ions?
• How can you test for carbonate ions, CO3^2-?
• Write an equation for the carbonate ion test
• How can you test for sulfate ions, SO4^2-?
• Why do you add HNO3 to test for halides and why not HCl?
• What are the observations for a positive test of sulfate ions, SO4^2-?
• CO3^2- (aq) + 2H+ (aq) → H2O (aq) + CO2 (g)
• Observations for a positive test of carbonate ions, CO3^2-

  • Fizzing
  • Limewater turns cloudy
• Negative ions
• Observations for a positive test of sulfate ions, SO4^2-

  • White precipitate of barium sulfate is produced
• Acidified AgNO3
• Test for sulfate ions, SO4^2-

  Add dilute hydrochloric acid and barium chloride to the sample
• Ba^2+ (aq) + SO4^2- (aq) → BaSO4 (s)
• Test for carbonate ions, CO3^2-

  1. Add strong acid to the sample

  2. Collect the gas produced

  3. Pass through lime water
• To remove CO2- Adding HCl would add Cl- ions, giving a false positive result
• Test for a halide ion

  1. Dissolve the sample in water

  2. Add aqueous silver nitrate

  3. Record the colour change

  4. If difficult to distinguish the colour, add aqueous ammonia, first dilute ammonia then concentrated ammonia

  5. Note the solubility of precipitate
• Result and equation for I- test

  • Yellow precipitate, insoluble in concentrated and dilute aqueous ammonia
  • Ag+ (aq) + I- (aq) → AgI (s)
• Result and equation for Cl- test

  • White precipitate, soluble in dilute aqueous ammonia
  • Ag+ (aq) + Cl- (aq) → AgCl (s)
• Cations are also known as
• Observations for positive ammonium ions test

  • Red litmus paper turns blue
  • Ammonia has a pungent smell
• Order of testing for carbonate, sulfate, and halide ions

  1. Carbonate test

  2. Sulfate test

  3. Halide test

  4. Because barium ions form insoluble precipitate of BaCO3 and silver ions form insoluble precipitate of Ag2SO4
• Result and equation for Br- test

  • Cream ppt, soluble in concentrated aqueous ammonia only
  • Ag+ (aq) + Br- (aq) → AgBr (s)
• Equation for ammonium ions test

  • NH4+ (aq) + OH- (aq) → NH3 (aq) + H2O (aq)
• Test for ammonium ions, NH4+

  1. Add sodium hydroxide to the sample and warm it

  2. Test the gas produced with red litmus paper
• Test for halide ions

  1. Dissolve the sample in water

  2. Add aqueous silver nitrate

  3. Record the colour change

  4. If difficult to distinguish the colour, add aqueous ammonia (first dilute then concentrated)

  5. Note the solubility of precipitate