3.6 Organic Analysis

• how do you test for alcohols?

  using acidified potassium dichromate

  change from orange to green
• how do you test for aldehydes and ketones using fehlings?

  Aldehydes - blue solution to brick red precipitate

  Ketones - no visible change
• how do you test for aldehydes and ketones using tollens' reagent?

  aldehydes - silver mirror

  ketones - no visible change
• how do you test for alkenes?

  using bromine water

  brown -> colourless
• how do you test for carboxylic acids?

  using carbonate, reacts by the following equation:

  CO32- + 2H+ -> CO2 + H2O

  bubble gas produced through limewater and it will turn cloudy
• what is mass spectrometry used for?

  find the relative molecular mass (Mr) of a compound
• what do peaks in mass spec show?

  peaks show fragments of the original molecule. last peak is the M+1 peak or the molecular ion peak. this is the same as the relative molecular mass of the molecule
• what is high resolution mass spectrometry used for?

  identifying different molecules with the same molecular mass rounded to the nearest whole number
• what does infrared spectrometry use?

  infrared radiation to increase the vibrational energy of covalent bonds in a sample
• what does the frequency of infrared radiation absorbed by a covalent bond depend on?

  1. the atoms that are either side of the bond

  2. the position of the bond in the molecule (e.g. OH in alcohols and OH in carboxylic acids)
• what is the fingerprint region and where does it lie?

  between 500 - 1500cm-1
• how is infrared linked to global warming?

  greenhouse gases absorb infrared radiation and re-emit this back towards the earth