chemical analysis

• Pure substance


  A single element or compound, not mixed with any other substance
• Pure substances


  • They melt and boil at specific temperatures
  • Melting and boiling point data can be used to distinguish pure substances from mixtures
• Pure substance (everyday language)


  Substance that has had nothing added to it, so it is unadulterated and in its natural state
• Formulation


  Mixture that has been designed as a useful product
• Many products are complex mixtures in which each chemical has a particular purpose
• Making formulations


  Mixing the components in carefully measured quantities to ensure the product has the required properties
• Chromatography


  Used to separate mixtures and give information to help identify substances
• Chromatography


  • 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
• Pigment


  Solid, coloured substance
• The more soluble a substance is, the further up the paper it travels
• Paper chromatography separates different pigments in a coloured substance
• hydrogen test:

  • use a burning splint held at the open end of the test tube of the gas
  • creates a squeaky pop sound
• test for oxygen:

  • use 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
  • it will turn milky cloudy
• test for chlorine:

  • use a damp litmus paper
  • when damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
• Flame tests


  Can be used to identify metal ions
• If a sample containing a mixture of ions is used, some flame colours can be masked (you won't be able to see them)
• Metal hydroxides


  • Aluminium, calcium and magnesium ions form a white precipitate with NaOH
  • Only aluminium's precipitate dissolves when excess NaOH is added
  • Copper(II) produces a blue precipitate
  • Iron(II) produces a green precipitate
  • Iron(III) produces a brown precipitate
• Forming metal hydroxides


  1. Metal ion + OH- -> Metal(OH)n

  2. Need as many OH- ions as the charge on the metal ion

  3. The Na from the NaOH and whatever the metal ion was bonded to will react to form a compound together
• 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
• Identifying halides


  1. Add dilute nitric acid, followed by silver nitrate solution

  2. Chloride gives a white precipitate

  3. Bromide gives a cream precipitate

  4. Iodide gives a yellow precipitate
• Sulfates


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


  • Accurate, sensitive and rapid, making them advantageous compared to chemical tests
  • Used to detect and identify elements and compounds
• Flame emission spectroscopy


  • Example of an instrumental method 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 and measure their concentrations
• Flame test results:

  • lithium - crimson
  • sodium - yellow
  • potassium -lilac
  • calcium -orange red
  • copper -green