Unit 8:Chemical analysis

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  • chemical analysis
    • flame tests
      • if a sample contains a mixture of ions, the colours could be masked
      • colours
        • copper - Green
        • Calcium - Brick red
        • lithium - crimson
        • Potassium - lilac
        • Sodium - yellow
    • Chromotography
      • involves a stationary phase and a mobile phase
      • Rf=distance moved by substance divided by the distance moved by the solvent
      • different components have different Rf values
      • providing the same temp and solvent are used, the Rf value for a specific compound is constant
      • separates mixtures into their constituent components
      • pure substances produce a single spot in all solvents
      • can be used to identify artificial colours
    • pure substances and mixtures
      • A pure substance is one made up of just one substance, either an element or a compound
      • formulations are mixtures that have been carefully designed to have specific properties
      • the components in a formulation are heavily controlled
      • impure substances are mixtures
      • the melting or boiling points of an element or compound are called its fixed points
    • gas tests
      • hydrogen - when mixed with air, burns with a squeaky pop
      • Chlorine - turns damp indicator paper white
      • Oxygen - relights a glowing splint
      • Carbon dioxide - When bubbled through lime water, turns it cloudy
    • Precipitation of metal ions
      • Aluminium (aluminium hydroxide) white precipitate redissolves in excess hydroxide solution
      • Calcium (calcium hydroxide) white precipitate
      • Magnesium (magnesium hydroxide) white precipitate
      • Copper(II) (copper(II) Hydroxide) light blue precipitate
      • Iron(II) (iron(II) hydroxide) green precipitate
      • Iron(III) (iron(III) hydroxide) brown precipitate
    • required practicals
      • investigate how paper chromatography can be used to separate.
        • 1. draw a start line in pencil on absorbent paper
        • 2. Put samples of 5 food colourings and the unknown substance on the line,
        • 3. dip the paper into solvent (water)
        • 4. wait for the solvent to travel to the top of the paper
        • 5. Identify solvent x by cross comparing
      • Identify the ions in a single ionic compound using chemical tests
        • 1. Heat a piece of nichrome wire in a Bunsen flame and then dip it in concentrated hydrochloric acid o clean it.
        • 2.Dip the wire in the compound
        • 3.place it into the Bunsen flame and observe the colour
    • metal hydroxides
      • AlCl3+3NaOH->Al(OH)3+3NaCl
      • CaCl2+2NaOH->Ca(OH)+2NaCl
      • MgCl2+2NaOH->Mg(OH)+2NaCl
    • Tests for anions
      • carbonate test
        • sodium carbonate solution in a test tube and limewater in another. add a few drops of hydrochloric acid to the first test tube and collect gas to bubble through the limewater
        • sodium carbonate solution will present a white precipitate
        • A white precipitate means carbon dioxide present
      • halide test
        • pour sodium chloride solution, sodium bromide solution and sodium iodide solution into three separate test tubes
        • add a few drops of silver nitrate into each test tubes
        • sodium chloride solution presents a white precipitate
        • Sodium bromide solution presents a cream precipitate
        • Sodium iodide solution presents a yellow precipitate
      • sulphate test
        • pour sodium sulphate into a test tube
        • add a few drops of barium chloride solution
        • sodium sulphate solution present a white precipitate

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