organic analysis

• acidified potassium dichromate is K2Cr2O7
• You can use K2Cr2O7 to test for alcohols

  should oxidise primary and secondary alcohols from orange (Cr2O7 2-) to green(Cr 3+)
• aledhyde made from primary alcohol

  ketone made from secodary alcohol

  when both alcohols have the same colour change, use fractional distillation to collect products and then test
• you can use fehling's solution to test for aldehydes.
• Fehling's is originally blue because of the Cu 2+ ions present
• Fehling's must be added to solution WARM.

  If aldehydes are present you should see a colour change from blue to brick- red
• Tollen's reagent can be used to differentiate between aldehydes and ketones
• tollen's is made by silver nitrate solution(colourless) + NaOH ( to make brown precipitate) + dilute ammonia (back to colourless)
• Tollen's reagent added to aldehyde should form 'silver mirror'
• bromine water can be used to test for alkenes
• add bromine to alkene should turn solution from brown to colourless

  product formed is dibromoalkane
• mass spectrometry is used to find the relative molecular mass of a compound
• Last peak of a mass spec graph is the M+1 peak. this shows the relative molecular mass of the molecule
• high resolution mass spectrometry is used to identify different molecules with the same molecular mass
• IR spectroscopy uses infrared radiation to increase the vibrational energy of covalent bonds
• the frequency of the infrared radiation absorbed depends on the

  • atom on either side of the bond
  • position of the bond in the molecule
• the fingerprint region of IR spectrum graphs allows us to identify specific molecules
• the fingerprint region lies between 500cm-1 - 1500cm-1
• you can compare the fingerprint region against a library of spectra to find what is the exact molecule
• extra peaks in the fingerprint region indicates there are impurities
• greenhouse gases absorb infrared radiation
• EM radiation reaches the Earth and is absorbed by the land. It gets re-emitted as infrared. This then gets absorbed by the greenhouse gases and gets re-emitted to the Earth.