C4.2 mindmap ~ identifying products of chemical reactions

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  • Chemistry - C4.2 ~ identifying products of chemical reactions
    • Detecting cations
      • Flame test:  Clean loop and dip it into test powder.  Hold in roaring blue flame for 10 secs.  Record flame colour.
        • Li+ = red
        • Na+ = yellow
        • K+ = lilac
        • Ca+ = orange/red
        • Cu^2+ = turquoise
      • Hydroxide precipitate test:  Put metal ion solution in a test tube and add sodium hydroxide solution. Note the precipitate colour formed.
        • Fe^2+ = green
        • Fe^3+ = orange/brown
        • Cu^2+ = blue
        • Ca^2+ = white
          • Tell apart as Zn^2+ precipitate will dissolve in excess sodium hydroxide
            • Zn^2+ = white
        • Zn^2+ = white
    • Detecting anions
      • Testing for halide ions:  Add a few drops of dilute nitric acid and a few drops of silver nitrate solution.  Record colour of precipitate.
        • Cl- = white
        • Br- = cream
        • I- = yellow
      • Testing for sulfate ions:  Add a few drops of dilute HCl acid and a few drops of barium chloride solution.
        • If sulfate ions present, white precipitate formed
      • Testing for carbonate ions:  Add a few drops of dilute HCl acid and look for bubbles.  Bubble gas through limewater.
        • If limewater turns cloudy from CO2 produced, carbonate ions were present
    • Gas tests
      • Hydrogen: lighted splint pops
      • Oxygen: glowing splint relights
      • Chlorine: damp blue litmus paper turns red then white
      • Carbon dioxide: limewater turns cloudy
    • Instrumental methods of analysis
      • Interpreting a gas chromatogram
        • Each peak represents a substance in the mixture
        • Area under each peak shows amount
      • Interpreting a mass spectrometer
        • Can measure the masses of atoms/ molecules and is used to analyse isotope amounts and molecule structure.
          • Sample molecules ionised by machine to form molecular ions
            • May break up to form fragments which the machine can separate and detect.
        • each peak represents a molecule fragment
        • Far right peak represents molecular ion
          • Mass to charge ratio of this = Mr of the molecule
      • Advantages
        • sensitive - can detect small amounts
        • Very accurate
        • Work quickly and can run all the time


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