Organic Analysis

• This video is for AQA organic analysis
• The presenter is Chris Harris from Alawis tutors
• The purpose of the video is to provide a revision of the topic of organic analysis
• The presenter has created PowerPoint slides that can be purchased to enhance revision or supplement learning
• Testing for alcohols


  1. Use acidified potassium dichromate

  2. Oxidises primary and secondary alcohols, not tertiary

  3. Primary and secondary alcohols both turn orange to green

  4. Need to do fractional distillation to collect products

  5. Test products to see if aldehyde or ketone formed
• Aldehydes


  Made from oxidation of primary alcohols
• Ketones


  Made from oxidation of secondary alcohols
• Testing for aldehydes and ketones


  1. Use Fehling's solution

  2. Blue solution turns brick red precipitate with aldehydes

  3. Remains blue with ketones
• Testing for aldehydes and ketones

  1. Use Tollens' reagent

  2. Colourless solution, add NaOH then NH3

  3. Silver precipitate forms with aldehydes, no precipitate with ketones
• Testing for alkenes


  1. Add bromine water

  2. Colourless solution forms, indicating presence of alkene
• Testing for carboxylic acids

  1. Add carbonate

  2. Fizzing and carbon dioxide gas produced, indicating carboxylic acid
• Mass spectrometry


  • Best used to find relative molecular mass (M)
  • Gives mass to charge ratio (m/z) of fragments
• Molecular ion peak


  Peak showing mass of unfragmented molecule
• High resolution mass spectrometry

  • Can distinguish molecules with same nominal molecular mass
  • Gives mass to higher decimal places
• High resolution mass spectrometry


  Useful when identifying different molecules with the same molecular mass rounded to the nearest whole number
• Standard mass spectrometry


  Gives mass to the nearest whole number
• High resolution mass spectrometry


  Can measure mass to several decimal places
• Molecules with same molecular mass

  • Ethanol (CH3CH2OH)
  • Propane (C3H8)
• Ethanol and propane both have a molecular mass of 44 to the nearest whole number
• High resolution mass spectrometry can distinguish ethanol and propane by measuring the precise molecular mass to 4 decimal places
• Infrared (IR) spectroscopy


  Uses infrared radiation to increase the vibrational energy of covalent bonds in a sample
• Factors affecting frequency of infrared radiation absorbed by a covalent bond

  • Atoms either side of the bond
  • Position of the bond in the molecule
• Exam data sheet provides information on wave numbers for different bonds
• Infrared spectrum of ethanoic acid

  • Peak at ~3000 cm^-1 suggests presence of OH group in acid
  • Peak at ~1700 cm^-1 suggests presence of carbonyl group
• Fingerprint region in infrared spectrum

  Region between 500-1500 cm^-1 where the size and position of peaks is unique to each molecule
• Presence of extra peaks in fingerprint region indicates impurities in the sample
• Greenhouse gases in the atmosphere

  Absorb infrared radiation emitted from the Earth's surface, causing the greenhouse effect and global warming
• Greenhouse gases like CO2, CH4, H2O absorb infrared radiation due to their covalent bonds
• Human activities like burning fossil fuels and landfill decomposition are increasing greenhouse gas levels and causing global warming