Chem 2

  • Created by: A.B.
  • Created on: 15-04-13 18:54
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  • Chemistry Unit 3 Part 2
    • Analysis and Synthesis
      • Tests for positive ions
        • Most Group 1 and Group 2 metals can be identified in their compounds using flame tests.
          • Lithium (Li+) = Crimson
          • Sodium (Na+) = Yellow
          • Potassium (K+) = Lilac
          • Calcium (Ca2+) = Red
          • Barium (Ba2+) = Green
        • Sodium hydroxide solution can be used to identify different metal ions, depending on the precipitate that is formed.
          • Aluminium, calcium and magnesium ions all form white precipitates if added to sodium hydroxide.
          • If more sodium hydroxide is added, the aluminium ions will dissolve. Then the magnesium ions and calcium ions can be distinguished using a flame test.
            • Aluminium, calcium and magnesium ions all form white precipitates if added to sodium hydroxide.
          • If sodium hydroxide is added to copper 2+, iron 2+ or iron 3+, a coloured precipitate is formed.
            • Copper (2+) = light blue (precipitate).
            • Iron 2+ = light green -> brown (precipitate)
            • Iron 3+ = reddish brown
      • Tests for negative ions
        • We identify carbonates by adding dilute acid, which produces carbon dioxide gas. The gas turns limewater cloudy.
        • We identify halides by adding nitric acid, then silver nitrate solution. This produces a precipitate of silver halide.
          • Chloride = white precipitate
          • Bromide = cream precipitate
          • Iodide = pale yellow precipitate
          • We add the nitric acid to remove any carbonate ions.
        • We identify sulfates by adding hydrochloric acid, then barium chloride solution. This produces a white precipitate of barium sulfate.
      • Titrations
        • Titration is used to measure accurately how much acid and alkali react together completely.
          • They form a salt + water
        • The point at which an acid-alkali reaction is complete is called the end of the reaction.
        • We us an indicator to show the end point of the reaction between an acid and an alkali.
      • Chemical analysis
        • Scientists working in environmental monitoring medicine and forensic science all need to analyse substances.
          • Drugs,  paints, remnants of an explosion, fire debris, gunshot debris, fibres, soil samples, toxic chemicals, biological toxins.
        • The results of their analysis are often matched against existing databases to identify substances (or suspects in the case of forensics).


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