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chemical analysis (purity & formulations (formulations are mixtures…

- - - - the stationary phase is the paper (often filter paper) & the mobile phase is the solvent (e.g. ethanol, water).
        
        the amount of time the molecules spend in each phase depends on:
        
        how soluble they are in the solvent
        
        how attracted they are to the paper.
        
        molecules with a higher solubility in the solvent & which are less attracted to the paper will spend more time in the mobile phase & will be carried further up the paper.
    - - the mobile phase moves through the stationary phase & anything dissolved in the mobile phase moves with it. how quickly a chemical moves depends on how it is distributed between the two phases - whether it spends more time in the mobile or stationary phase.
        
        the chemicals that spend more time in the mobile phase move further through the stationary phase.
        
        the components in a mixture normally separate through the stationary phase, so long as all the components spend different amounts of time in the mobile phase.
        
        the number of spots may change in different solvents as the distribution of the chemical will change depending on the solvent - a pure substance will only form one spot in any solvent as there is only one substance in the sample.
  - - - B is distance from the baseline (origin) to the centre of the spot.
        A is baseline --> solvent front
- - - - the light passes through a spectroscope which can detect different wavelengths of light to produce a line spectrum.
        
        the combination of wavelengths emitted by an ion depends on its charge & its electron arrangement.
        no two ions have the same charge & the same electron arrangement so different ions emit different wavelengths of light so each ion produces a different pattern of wavelengths & has a different line spectrum.
        
        the intensity of the spectrum indicates the concentration of that ion in solution so the line spectrum can be used to identify ions in solution & calculate their concentrations.
- - - - carbonates are substances that contain CO3^2- ions.
        
        test whether a solution contains carbonate ions by putting a sample in a test tube & using a dropping pipette to add a couple of drops of dilute acid.
        
        then connect the test tube to a test tube of limewater.
        
        if carbonate ions are present, carbon dioxide will be released that will turn the limewater cloudy when it bubbles through it
        e.g. Na2CO3 (aq) +2HCl (aq) --> CO2 (g) + 2NaCl(aq) + H2O (l)
    - - to identify sulfate ions (SO4^2-):
        
        use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution (BaCl2) to a test tube containing the mystery solution.
        
        if sulfate ions are present, a white precipitate of barium sulfate will form.
        Ba^2+ (aq) + SO4^2- --> BaSO4(s)
    - - to identify a halide ion, add a couple of drops of dilute nitric acid (HNO3) followed by a couple of drops of silver nitrate solution (AgNO3) to the solution.
        
        Ag+ + Cl- --> AgCl (s) chloride gives a white precipitate of silver chloride
        
        a bromide gives a cream precipitate of silver bromide
        
        an iodide gives a yellow precipitate of silver iodide
- - - - lithium ions Li+ --> crimson flame
        
        sodium ions Na+ --> yellow flame
        
        potassium ions K+ lilac flame
        
        calcium ions Ca2+ orange-red flame
        
        copper ions Cu2+ green flame
      - clean a platinum wire loop by dipping it in some dilute HCl & then holding it in a blue flame from a Bunsen burner until it burns without any colour.
        
        dip the loop into the sample you want to test & put it back in the flame, record the colour of the flame.
        
        use these colours to detect & identify different ions but it only works for samples that contain a single metal ion.
        
        if the sample tested contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others.
  - - - calcium, Ca2+ ions --> white precipitate --> Ca2+(aq) + 2OH-(aq) --> Ca(OH)2 (s)
        
        copper (II), Cu2+ blue precipitate Cu2+(aq) + 2OH- (aq)--> Cu(OH)2
        
        iron (II), Fe2+ green Fe2+ (aq)+ 2OH- (aq) --> Fe(OH)2 (s)
        
        iron (III) Fe3+ brown Fe3+ (aq) +3OH- (aq) --> Fe(OH)3 (s)
        
        aluminium Al3+ white at first but then redissolves in excess NaOH to form a colourless solution Al3+ (aq) + 3OH- (aq) --> Al(OH)3 (s)
        
        magnesium Mg2+ white Mg2+ (aq) + 2OH- (aq) --> Mg(OH)2 (s)