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TESTS FOR IONS & GASES, A+special+test+for+oxygen!, Edex_SepSci_0148_…

- - - - bleaches dyes
  - - - combines violently with oxygen when lit
  - - - fuels burn more readily in it than air
  - - - choking smell
        
        will reduce potassium manganate(VII) ion to colorless potassium manganese(II) ions
- - - - if cation is present: ammonia gas is given off
        (turns litmus paper blue)
        
        ionic equation:
        NH4+ (aq) + OH- (aq) → NH3 (g) + H2O (l)
  - - - if cation is present: pale blue precipitate forms. adding more (excess) sodium hydroxide has no effect
        
        ionic equation:
        Cu2+ (aq) + 2OH- (aq) → Cu(OH)2 (s)
    - - if cation is present: a pale blue precipitate forms. it dissolves again if you add more (excess) ammonia, giving a deep blue solution
        
        the precipitate dissolves again in excess ammonia because a soluble complex ion forms (ion with several negative ions / molecules around the positive metal ion
  - - - if cation is present: pale green precipitate forms
        
        ionic equation:
        Fe2+ (aq) + 2OH- (aq) → Fe(OH)2 (s)
  - - - if cation is present: red-brown precipitate forms
        
        ionic equation:
        Fe3+ (aq) + 3OH- (aq) → Fe(OH)3 (s)
  - - - if cation is present: white precipitate forms. it dissolves again if you add more (excess) sodium hydroxide, giving a colorless solution
        
        the precipitate dissolves in excess sodium hydroxide because aluminium hydroxide is amphoteric (reacts with acids & alkalis)
        
        ionic equation:
        Al3+ (aq) + 3OH- (aq) → Al(OH)3 (s)
    - - if cation is present: white precipitate forms. adding more (excess) ammonia has no effect
  - - - if cation is present: white precipitate forms in each case. in each case it dissolves again if you add more (excess) of the reagent, giving a colorless solution
        
        the precipitate dissolves again in excess sodium hydroxide because zinc hydroxide is amphoteric.
        it dissolves again in excess ammonia because a soluble complex ion forms
        
        ionic equation:
        Zn2+ (aq) + 2OH- (aq) → Zn(OH)2 (s)
  - - - if cation is present: white precipitate forms. adding more (excess) sodium hydroxide has no effect
        
        ionic equation:
        Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)
    - - if cation is present: no precipitate / very slight white precipitate
  - - - if cation is present: grey-green precipitate forms.
        it dissolves again if you add more sodium hydroxide, giving a green solution.
        
        the precipitate dissolves in excess sodium hydroxide because chromium hydroxide is amphoteric
        
        ionic equation:
        Cr3+ (aq) + 3OH- (aq) → Cr(OH)3 (s)
    - - if cation is present: grey-green precipitate forms. it dissolves again if you add more ammonia, giving a purple solution
        
        the precipitate dissolves again in excess ammonia because a soluble complex ion forms
- - - - test: add an equal volume of dilute nitric acid to a small amount of the solution. then add aqueous silver nitrate
        
        iodide ions, I-
        
        Ag+ (aq) + Cl- (aq) → AgCl (s)
        
        yellow precipitate
        
        chloride ions, Cl-
        
        Ag+ (aq) + Br- (aq) → AgBr (s)
        
        white precipitate
        
        bromide ions, Br-
        
        Ag+ (aq) + I- (aq) → AgI (s)
        
        cream precipitate
  - - - if sulfate ions are present: barium sulfte is insoluble, so a white precipitate will form
        
        ionic equation:
        Ba2+ (aq) + SO4 2- (aq) → BaSO4 (s)
  - - - if sulfite ions are present: sulfur dioxide gas is given off
        
        ionic equation:
        SO3 2- (aq) + 2H+ (aq) → H2O (l) + SO2 (g)
        
        test for sulfur dioxide gas: soak a piece of filter paper in acidified aqueous potassium manganate(VII) [purple]. place it in the mouth of the test-tube. the color turn from purple → colorless
  - - - if nitrate ions are present: ammonia gas is given off
        
        ionic equation:
        8Al (s) + 3NO3- (aq) + 5OH- (aq) + 2H2O (l) → 3NH3 (g) + 8AlO2- (aq)
  - - - if carbonate ions are present: the mixture bubbles and carbon dioxide gas is given off, turning limewater milky
        
        ionic equation:
        2H+ (aq) + CO3 2- (aq) → CO2 (g) + H2O (l)