Analysis & quantitative Chemistry

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  • Analysis & Quantitative Chemistry
    • Flame tests
      • Used to identify metal ions
      • Green - Barium, Brick Red - Calcium, Crimson - Lithium, Lilac - Potassium, Yellow - Sodium
      • Heat & dip nichrome wire in concentrated hydrochloric acid to clean
        • Dip wire in compound
          • Put in bunsen flame
    • Reacting carbonates with dilute acid
      • Carbonates react with dilute acids to form CO2 (and a salt and water). CO2 turns lime water cloudy
      • e.g. Calcium Carbonate + hydrochloric acid = calcium chloride + carbon dioxide + water
    • Precipitation of Metal Ions
      • Metal compounds in solution contain metal ions
        • Some form precipitates i.e. insoluble solids that come out of solution when sodium hydroxide's added
      • Al3+ (aq) - white precipitate which dissolves in excess sodium hydroxide
      • Ca2+ (aq) - white, Mg2+ - white, Cu2+ (aq) - blue, Fe2+ (aq) - green, Fe3+ (aq) - Brown
        • Fe2+ = Iron ( II) & Fe3+ = Iron (III). All precipitates formed are hydroxides e.g. Calcium hydroxide
    • More examples of precipitation
      • If dilute hydrochloric acid and barium chloride are added to a solution containing sulfate ions, a white precipitate of barium sulfate is produced
      • Precipitates with silver nitrate solution can be produced by Halide ions (chloride, bromide, iodide ions) in solution in presence of dilute nitric acid:
      • Silver Chloride - white, Silver Bromide - cream, Silver Iodide - yellow
    • Titration
      • Used to find out how much of an acid is needed to neutralise an alkali
      • Neutralisation = hydrogen ions (H-) from acid and hydroxide ions (OH-) from alkali form water
      • Clean pippette to measure out known & accurate volume of alkali
        • Put alkali in clean conical flask.
          • Add suitable indicator e.g. phenolphthalein
            • Put acid in burette (cleaned with acid) and take reading of volume.
              • Add acid to alkali until indicator changes to green (neutral). This is called the end point.
                • Take final reading of volume in burette.
                  • Subtract final reading from initial reading to find volume of acid added
                    • Method can be used to obtain salt without using an indicator. Method can be repeated to check results.
    • Indicators
      • Different strength acids & alkalis can react together to form a neutral solution.
      • Suitable indicator for strong acids & alkalis = acid based (e.g. litmus)
    • Titration - Higher
      • can be used to find concentration of acid/alkali
        • You must know: relative volumes & concentration of other acid/alkali
      • 1) Write balanced equation for reaction to determine ratio of moles of acid to alkali involved
      • 2) Calculate no. of moles in solution of known volume & concentration ( you know the nuimber of moles in other solution from previous calc.)
      • Calculate concentration of other solution: Number of moles of solute (mol) / Volume of solution (dm^-3)


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