Organic Analysis


Uses of mass Spectrometry

  • Detecting drugs in athletes
  • Monitor/track pollutants
  • Locate oil deposits by testing rock samples
  • Assessing the damage on human genes via environment
  • Identify the country of origin of diamonds
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Mass Spectrometry

  • Can be used to find the molecular mass (Mr) ofa compound. 
  • The peak with the heighest mass/charge value (x-axis) is equal to the Mr.
  • The peak at highest m/z also equals the molecular ion.
  • X = Mass/Charge, Y = Relative abundance%

High resolution: 

  • Used to identify compounds that appear to have the same Mr when rounded.
  • Can measure the Mr to 4 decimal places.
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Infrared Spectroscopy

  • Pairs of atoms joined by a covalent bond continually vibrate at a specific frequency.
  • The vibrations have a frequency in the infrared regions of the electromagnetic spectrum. 
  • A beam of inrared radiation is shone onto the compound with increases the amplitude of the vibration.
  • Each bond has adifferent natural frequency vibration, enabling chemists to identify what is present. 
  • Y = Transmittance%, X = Wavenumber cm-1.
  • Functional groups can be found between 4000-1500cm-1. 
  • The fingerprint region = below 1500cm-1, is unique to a particular compound and is used to find out what it is using a computed database. Extra peaks in this region shows impurities. 
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Primary, Secondary or Tertiary alcohol

Test 1:

  • Add 10 drops of alcohol to 2cm3 of acidified potassium dichromate in a test tube.
  •  Warm mixture gently in a hot water bath.
  • Primary/Secondary = Turns from orange to green(P-aldehyde formed,S-ketone formed) Tertiary = doesn't change. 

Test 2:

  • Add excess alcohol to 2cm3 of acidified potassium dichromate in a round bottomed flask and attach to distillation apparatus. 
  • Gently heat flask , alcohol gets oxidised and the product will be distilled immediatly. Ketone or aldehyde will be produced

Test 3:

  • Add 2cm3 of Fehling's or Benedict's solution to 5 drops of aldehyde/ketone and put into a warm water bath. 
  • Aldehyde = brick red precipitate.
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Tollen's Reagent

  • Put 2cm3 of 0.10mol/dm-3 silver nitrate solution to a test tube.
  • Add a few drops of sodium hydroxide solution, light brown precipitate is formed. 
  • Add dilute ammonia solution until precipitate dissolves.
  • Place test tube in hot water bath and add 10 drops of aldehyde/ketone and wait.
  • Aldehyde = silver mirror, reduced the Ag+ ions to silver atoms.
  • Ketone = nothing happens 
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Test for alkenes

  • Testing for the presence of double bonds. 
  • Add 2cm3 to of solution to a test tube with 2cm3 of bromine water. 
  • Shake the test tube.
  • Alkene = orange to colourless
  • Alkane = nothing happens
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Test for carboxylic acids

  • Carboxylic acids react with carbonates to form a salt, carbon dioxide and water. 
  • Add 2cm3 of solution to a test tube
  • Add a spatula of solid sodium carbonate .
  • If the solution fizzes you can test what it is by feeding the gas produced into lime water. 
  • Carboxylic acid = Solution will fizz, lime water cloudy. 
  • Not carboxylic acid = nothing
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