C8 - chemical analysis

• what is a pure substance?

  a single element or compound not mixed with any other substances
• how do you know how pure a substance is?

  measuring the melting or boiling point and comparing it with the point of the pure substance

  the closer the melting/boiling point, the purer the substance
• how do impurities affect the melting point of a substance?

  the can lower the melting point

  broader melting point range
• what is a formulation?

  useful mixtures with a specific purpose made by following a formula
• how are formulations made?

  made my mixing the components in carefully measured quantities to ensure that the product has required properties
• what are examples formulations?

  fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
• what is chromatography?

  is used to separate mixtures and can give information to help identify substances
• what is the mobile phase?

  a substance the particles can move in - the solvent
• what is the stationary phase?

  a substance the particles cannot move in - the paper
• what is an Rf value?

  ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
• how do you calculate the Rf value?

  distance moved by substance ÷ distance moved by solvent
• how do you differentiate between a pure or impure substance?

  pure substances - produce on spot on the chromatogram

  impure substance - produces more than one spot on the chromatogram
• what is the method for chromatography?

  • draw a pencil line near the bottom of the paper - baseline
  • add samples of ink on the baseline
  • add to a beaker filler with solvent
  • place in beaker below the baseline and add a lid
  • allow solvent to seep up the paper
  • allow to dry and draw the solvent line
• why do some soluble dyes travel faster?

  more soluble, less attracted to the paper so they spend more time in the mobile phase
• why do some soluble dyes travel slower?

  less soluble means they are more attracted to the paper so they spend more time in the stationary phase
• what is the test for oxygen?

  glowing splint relights
• what is the test for chlorine?

  damp litmus paper is bleached
• what is the test for carbon dioxide?

  limewater turns cloudy
• what is the test for hydrogen?

  squeaky pop
• what colour flame does the cation lithium produce?

  crimson
• what colour flame does the cation sodium produce?

  yellow
• what colour do the cation potassium produce?


  lilac
• what colour does the cation calcium produce?

  red-orange
• what colour does the cation copper produce?

  green
• what colour does the cation calcium form when NaOH is added?

  white precipitate
• what colour does the cation aluminium form when NaOH is added?

  white precipitate
• what colour does the cation barium form when NaOH is added?

  cream precipitate
• what colour does the cation copper form when NaOH is added?

  blue precipitate
• what colour does the cation iron form when NaOH is added?

  yellow precipitate
• how do you test for carbonates?

  add dilute acid so carbon dioxide is formed
• how do you test for sulfates?

  barium chloride solution in the presence of dilute hydrochloric acid

  if sulfate ions are present, a white precipitate forms
• how do you test for halides?

  add a few drops of silver nitrate solution in the presence of dilute nitric acid

  test to see if lime water turns cloudy

  chloride - white precipitate of silver chloride

  bromide - cream precipitate of silver bromide

  iodide - yellow precipitate of silver iodine
• how does flame emission spectroscopy work?

  a sample is placed into a flame

  light is given out and passes through a spectroscope

  a line spectrum is produced
• how is light given out in flame emission spectroscopy?

  ions heat up and electrons gain energy

  electrons drop back to their energy levels and transfer energy as light
• how do you determine the concentration of the ion?

  the intensity of the spectrum
• what can the line spectrums be used for?

  can be used to identify ions in solutions and measure their concentrations
• what are instrumental methods?

  tests that use machines
• what are the advantages of using instrumental methods?

  very sensitive - can detect even small amounts of substances

  very fast - tests can be automated

  very accurate