organic analysis.

• test for alkenes;

  • add bromine water and shake
  • orange to colourless / decolourises
• test for haloalkane;

  • add aqeuous NaOH and warm gently
  • acidify with nitric acid ( HNO3)
  • add silver nitrate
  • coloured precipates are formed:

  AgCl = white

  AgBr= cream

  AgI = yellow
• test for alcohol;

  • add acidified k2cr2o7
  • orange to green
  • no change for tertiary alcohols
• test for aldehyde;

  • tollen's reagant
  • silver mirror

  OR

  • fehling's solution
  • blue to red
• test for carboxylic acid;

  • add sodium hydrogen carbonate
  • effervescence as co2 gas is produced
• mass spectrometry;

  • to identify unknown compounds
  • sample is bombarded with high energy e- , forming a molecular ion with charge 1+
  • the molecular ion can be further fragmented to form new ions, these are accelerated by an electric field
• m/z value is the mass divided by the charge
• smaller and more positive ions are deflected first and the most, as they are strongly attracted to the negative pole of the magnet
• each fragment is represented by a peak on the mass spectrum, with its own m/z value
• Infra-red spectroscopy;

  • used to identify compounds based on changes in vibration of atoms as they absorb IR
  • sample is irradiated with IR, where the different bonds absorb the radiation
• as bonds absorb IR, they will vibrate by stretching, bending or twisting
• molecules vibrate at specific frequencies, and will only absorb IR of the same frequency as their own
• why is silver nitrate acidified?

  • to remove ions that would interfere with the test
• barium sulfate can be used in medicine to block x-rays, this is because although barium ions are poisonous, barium sulfate is insoluble
• two species can have the same unprecise molecular mass
• the precise mr of carbon 12 is 12.00000 because c-12 is the reference isotope
• when proving that a sample contains two species;

  • calculate the precise mr of both
  • state that two peaks appear on the mass spectrum
• a spectrum may contain two peaks because isotopes are present
• state 2 differences between the IR Spectrum of a carboxylic acid and that of an alcohol?

  • The alcohol OH absorption (3550) is in a different region than the acid OH absorption (2500)
  • the C=O bond in the carboxylic acid has an absorption of 1680
• electrospray ionisation

  • sample is dissolved in volatile solvent
  • then passed through a needle at high voltage
  • each molecule will gain a H+