c.t.1

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  • Created by: priyasoni
  • Created on: 12-04-18 21:22
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  • Topic 1 - Chemical Analysis
    • purity and formulations
      • pure substance = single compound or element
      • pure substance has a specific fixed mp and bp
      • impure substances melt and boil over a range of temps.
      • Formulation = a complex mixture that has been designed as a useful product.
        • the quantity of each component is carefully measured so that each product has the properties we need.
        • e.g. fuels, paints, alloys, fertilisers, medicines, food
    • Paper Chromatography
      • physical process, no chemical reactions, no new substance made.
      • allows us to separate substances based on their different solubilites
      • >paper = stationary phase.  >solvent = mobile phase
      • chemicals strongly attracted to stationary phase won't move far
      • works because each chemical in the mixture will be attracted to the stationary phase to a different extent
      • chemicals weakly attracted will move further up the paper
      • draw the line in pencil, in pen the ink would move up the paper with the solvent
    • Testing for gases
      • Oxygen - place glowing splint in test tube and the splint relights.
      • Chlorine - damp litmus paper in test tube, litmus paper turns white
    • Flame Tests
      • Lithium = crimson
      • Sodium = yellow
      • potassium = lilac
      • Calcium = orange-red
      • copper = green
      • can be hard to distinguish colours with a low conc. of metal compound
      • mixture of metal ions can mask colour of the flame.
      • Flame Spectroscopy
        • sample of metal ion in solution is placed in the flame, light given out then passes through a machine called spectroscope
          • the spectroscope converts the light into a line spectrum
            • the postions of the lines in the spectrum are specific for a given metal ion
        • lines are more intense at a higher conc.
        • example of  an instrumental method
          • these methods are rapid, more rapid than flame tests
          • more sensitive, could work using a tiny sample of a metal compound.
          • accurate, more likely to identify a metal ion correctly than using flame test.
    • Metal Hydroxide Precipitates
      • Ca ions, Mg ions, Al ions + Sodium hydroxide all produce a white precipitate.
        • can't distinguish difference between the three.
        • Add excess sodium hydroxide solution : Al precipitate redissolves
        • Flame test for Ca
          • Ca(NO3)2 + 2NaOH ------> 2NaNO3 + Ca(OH)2
            • [Calcium] Nitrate (aq)+ Sodium hydroxide(aq) --> Sodium nitrate(aq) + [calcium] hydroxide(s).
              • Ca ions, Mg ions, Al ions + Sodium hydroxide all produce a white precipitate.
                • can't distinguish difference between the three.
                • Add excess sodium hydroxide solution : Al precipitate redissolves
                • Flame test for Ca
                  • Ca(NO3)2 + 2NaOH ------> 2NaNO3 + Ca(OH)2
                    • [Calcium] Nitrate (aq)+ Sodium hydroxide(aq) --> Sodium nitrate(aq) + [calcium] hydroxide(s).
        • Sodium Hydroxide Reactions
          • Copper II ions react to form blue  precipitate of copper (II) hydroxide
            • [Copper] (II) nitrate + Sodium Hydroxide --> Sodium Nitrate + [Copper] (ii) Hydroxide
            • Cu(NO3)2 + 2NaOH --> 2NaNO3 + Cu(OH)2
          • Iron (II) ions form a green precipitate of iron (II) hydroxide
            • [iron] (II) nitrate + Sodium Hydroxide --> Sodium Nitrate + [Iron] (II) Hydroxide
            • Fe(NO3)2 + 2NaOH --> 2NaNO3 + Fe(OH)2
          • Iron (III) ions react to form a brown precipitate of Iron (III) hydroxide
            • Fe(NO3)3 + 3NaOH --> 3NaNO3 + Fe(OH)3
            • [iron] (III) nitrate + Sodium Hydroxide --> Sodium Nitrate + [Iron] (III) Hydroxide
      • Identifying non-metal ions
        • Carbonate ions
          • Add dilute acid, produce CO2 and we see effervescence (fizzing) bubble the gas through lime water cloudy = co2
        • Halide ions
          • Dilute nitric acid and dilute silver nitrate solution, produce a precipitate of the silver halid, each halide = diff. coloured precipitate
          • Chloride = white    >Bromide =         cream             >  Iodide =              yellow
        • Sulfate Ions
          • Dilute HCl and barium chlorid solution. sulfate ions present = white pp.

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