Chemical Analysis

• what are pure substances

  a single element or compound that isnt mixed with any other substance

  • they melt + boil at specific temperatures + this can distinguish them from mixtures
  • they are unadulterated + in their natural state (e.g. pure milk)
• what are formulations


  mixtures that have been designed as useful product

  • products can be complex mixtures in which each chemical has a particular purpose
  • they are made by mixing the components in carefully measured quantities to ensure the product has the required properties
  • examples are medicines + fertilisers + paints
• what is chromatography


  process used to separate mixtures + provide information to help identify substances

  • involves a stationery + mobile phase
  • separation depends on the distribution of substances between phases
• what is an Rf value

  a ratio showing how far a solvent has moved

  • different compounds have different Rf values in different solvents, which helps identify the compound
  • compounds in a mixture may separate into different spots depending on the solvents but a pure compound will produce a single spot in all solvents
  • if the solvent moves a small distance, the Rf value will be smaller
  • if the solvent moves a long distance, the Rf value will be larger
• Rf value =

  distance moved by substance / distance moved by solvent
• what does a paper chromatography diagram show

  • separate + different pigments are in different coloured substances
  • compounds are separated by their relative speed in a solvent as they spread through paper
  • the more soluble a substance, the further up the paper it travels
  • the pigment used is a solid + coloured substance
• how can you test for hydrogen

  • use a burning splint held at the open end of a test tube of the gas
  • creates a 'squeaky pop' sound as hydrogen burns rapidly
• how can you test for oxygen

  • use a glowing splint inserted into a test tube of gas
  • splint will relight in oxygen
• how can you test for carbon dioxide

  • bubble the gas through limewater (aqueous calcium hydroxide)
  • it will turn cloudy for carbon dioxide
• how can you test for chlorine

  • place damp litmus paper into chlorine gas
  • the litmus paper will be bleached + turn white
• how can metal ions be found

  flame tests

  • if a sample contains a mix of ions, some flame colours will be masked + not visible
• which colour does lithium show in flame tests

  crimson
• which colour does sodium show in flame tests

  yellow
• which colour does potassium show in flame tests

  lilac
• which colour does calcium show in flame tests

  orange - red
• which colour does copper show in flame tests

  green
• how can you remember all the flame tests

  L--------------> lyrics (lithium)

  C--------------> can (crimson)

  S--------------> surround (sodium)

  Y--------------> your (yellow)

  P--------------> place (potassium

  L--------------> like (lilac)

  C--------------> choirs (calcium)

  O--------------> only (orange)

  C--------------> can (copper)

  G--------------> grasp (green)
• how can you test for metal hydroxides

  • aluminium + calcium + magnesium ions form a white precipitate with NaOH
  • aluminiums precipitate dissolves when excess NaOH is added
  • copper (II) creates a blue precipitate when excess NaOH is added
  • iron (II) creates a green precipitate when excess NaOH is added
  • iron (III) creates a brown precipitate when excess NaOH is added
• what do equations for metal hydroxides look like

  Cu 2+ + 2OH- -> Cu(OH)2

  • you need as many OH- ions as the charge on the metal ion

  CuCl2 + 2NaOH -> Cu(OH)2 + 2NaCl

  • the Na from the NaOh + whatever the metal ion was bonded to will react to form a compound together
• how can you remember all the excess precipitates of metal hydroxides


  A--------------> all (aluminium)

  D--------------> dumbs (dissolves)

  C--------------> cant(copper)

  B--------------> believe (blue)

  I--------------> im (iron II)

  G--------------> going (green)

  I--------------> into (iron III)

  B--------------> buffets (brown)
• how can you test for carbonates

  carbonates + dilute acids -> carbon dioxide

  • the gas can be bubbled through limewater
  • if the limewater turns cloudy the gas is CO2
• how can you test for halides

  • add dilute nitic acid + silver nitrate solution after
• what precipitate does chlorine give off

  a white precipitate
• what precipitate does bromide give off

  a cream precipitate
• what precipitate does iodine give off

  a yellow precipitate
• how can you remember all the precipitates of halides

  C--------------> can (chlorine)

  W--------------> we (white)

  B--------------> break (bromide)

  C--------------> cars (cream)

  I--------------> in (iodide)

  Y--------------> yugoslavia (yellow)
• how can you test for sulphates

  • add dilute hydrochloric acid + barium chloride solution after
  • a white precipitate will form when sulphate ions are present in the solution
• how are instrumental methods useful in identifying elements + compounds

  they are advantageous compared to chemical tests

  • accurate
  • sensitive
  • rapid
• what is flame emission spectroscopy

  an example of an instrumental method used to analyse metal ions in solutions

  • sample is placed into a flame
  • the light given out is passed through a spectroscope
  • output is a line spectrum that is analysed to identify metal ions in the solution + measure their concentrations