C8 - Chemical Analysis

• Pure substances


  ● A pure substance = a single element or compound, not mixed with any other substance

  ● They melt and boil at specific temperatures

  ● This melting and boiling points data can be used to distinguish pure substances from mixtures

  ● In everyday language, a pure substance = substance that has had nothing added to it, so it is unadulterated and in its natural state, e.g. pure milk
• Formulations 


  ● A formulation = mixture that has been designed as a useful product

  ● Many products are complex mixtures in which each chemical has a particular purpose

  ● They are made by mixing the components in carefully measured quantities to ensure that the product has the required properties

  ● Examples are fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
• Chromatography

  ● Used to separate mixtures and give information to help identify substances

  ● Involves a stationary phase and a mobile phase

  ● Separation depends on the distribution of substances between the phases

  Rf value = distance moved by substance ÷ distance moved by solvent

  ● Different compounds have different Rf values in different solvents, which can be used to help identify the compounds

  ● Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents
• Paper Chromatography 


  • Analytical technique separating compounds by their relative speeds in a solvent as it spreads through paper.
  • The more soluble a substance is, the further up the paper it travels. Separates different pigments in a coloured substance.
• Test for hydrogen

  ● Use a burning splint held at the open end of a test tube of the gas

  • Creates a ‘squeaky pop’ sound (hydrogen burns rapidly)
• Test for oxygen

  ● Uses a glowing splint inserted into a test tube of the gas

  • Splint relights in oxygen
• Test for carbon dioxide 


  ● Bubble the gas through the limewater (calcium hydroxide (aq))

  - it will turn milky (cloudy)
• Test for chlorine

  ● Use damp litmus paper

  • When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
• Flame Tests

  • Lithium = crimson
  • Sodium = yellow
  • Potassium = lilac
  • Calcium = orange/red
  • Copper = green
  • remember: c ya later og
• Metal hydroxides

  • Aluminium, calcium and magnesium ions form a white precipitate with NaOH.
  • Only aluminium's precipitate dissolves when excess NaOH is added.
  • Copper(Il) produces a blue precipitate
  • Iron(Il) produces a green precipitate
  • Iron(IIl) produces a brown precipitate
  • equations: e.g. Cu'* + 20H -> Cu(OH), you need as many OH ions as the charge on the metal ion the Na from the NaOH and whatever the metal ion was bonded to will react to form a compound together: e.g. CuCl, + 2NaOH -> Cu(OH), + 2NaCl
• Carbonates

  • Carbonates react with dilute acids

  to create carbon dioxide.

  • This gas can be bubbled through limewater, if the limewater goes cloudy, the gas is CO2
• Halides

  • First add dilute nitric acid, followed by silver nitrate solution
  • Chloride gives a white precipitate
  • Bromide gives a cream precipitate
  • lodide gives a yellow precipitate
  • Remember: Cats With Brains Can Ideally Yodel
• Sulfates

  • First add dilute hydrochloric acid, followed by barium chloride solution
  • A white precipitate will form when sulfate ions are in this solution
• Instrumental methods

  • Elements and compounds can be detected and identified using instrumental methods
  • These are: accurate, sensitive and rapid, making them advantageous compared to chemical tests
• Flame Emission Spectroscopy 


  • used to analyse metal ions in solutions
  • Sample is put into a flame and the light given out is passed through a spectroscope
  • Output is a line spectrum that can be analysed to identify the metal ions in the solution
  • Stronger the colour, higher the concentration