Qualitative Analysis

• What are anions also known as?

  Negative ions
• How can you test for carbonate ions, $CO_3^{2-}$?


  Add strong acid to the sample, collect the gas produced, and pass it through lime water
• What are the observations for a positive test of carbonate ions, $CO_3^{2-}$?


  Fizzing and limewater turns cloudy
• Write an equation for the carbonate ion test.


  $CO_3^{2-} (aq) +$$2H^+$$(aq) → H_2O (aq) +$$CO_2 (g)$
• How can you test for sulfate ions, $SO_4^{2-}$?


  Add dilute hydrochloric acid and barium chloride to the sample
• What are the observations for a positive test of sulfate ions, $SO_4^{2-}$?


  A white precipitate of barium sulfate is produced
• Write an equation for the sulfate ion test.

  $Ba^{2+} (aq) +$$SO_4^{2-} (aq) → BaSO_4 (s)$
• What do you use to test for halide ions?

  Acidified AgNO3
• Why do you add HNO3 to test for halide ions and not HCl?

  To remove $CO_3^{2-}$ ions, as adding HCl would introduce Cl- ions, giving a false positive result
• How can you test for a halide ion?

  Dissolve the sample in water, add aqueous silver nitrate, record the colour change, and note the solubility of the precipitate
• What is the result and equation for the Cl- test?

  White precipitate, soluble in dilute aqueous ammonia; $Ag^+$$(aq) +$$Cl^- (aq) → AgCl (s)$
• What is the result and equation for the Br- test?

  Cream precipitate, soluble in concentrated aqueous ammonia only; $Ag^+$$(aq) +$$Br^- (aq) → AgBr (s)$
• What is the result and equation for the I- test?

  Yellow precipitate, insoluble in concentrated and dilute aqueous ammonia; $Ag^+$$(aq) +$$I^- (aq) → AgI (s)$
• When testing for carbonate, sulfate, and halide ions, in which order should the tests be carried out and why?

  1. Carbonate test, 2. Sulfate test, 3. Halide test; because barium ions form an insoluble precipitate of BaCO3 and silver ions form an insoluble precipitate of Ag2SO4
• What are cations also known as?

  Positive ions
• How can you test for ammonium ions, $NH_4^+$?


  Add sodium hydroxide to the sample and warm it, then test the gas produced with red litmus paper
• What are the observations for a positive ammonium ions test?

  Red litmus paper turns blue and ammonia has a pungent smell
• Write the equation for ammonium ions test.

  $NH_4^+$$(aq) +$$OH^- (aq) → NH_3 (aq) +$$H_2O (aq)$