3.3.6 Organic Analysis

Cards (16)

  • Testing for alkenes:
    • Shake with bromine water
    • result is bromine water is decolourised (orange to colourless)
  • Testing for Haloalkanes:
    • Add NaOH (aq) and warm, acidify with HNO3 , add AgNO3 (aq)
    • Result: precipitate of AgX (for Cl=white, for Br=cream, for I=yellow)
  • Testing for alcohols:
    • Add acidified K2Cr2O7 (potassium dichromate(VI)) and heat
    • Result: colour change from orange to green for 1 0 and 20 alcohols (note: no change for 30 alcohols)
  • Testing for aldehydes (2 ways):
    1. Warm with Fehling’s solution, result: brick red ppt forms (from blue solution)
    2. Warm with Tollens’ reagent, result: “silver mirror” (Ag(s) ppt) forms
  • How do you test for carboxylic acids?
    • Add Na2CO3 (aq)
    • result: CO2 (g) given off - effervescence
  • Mass spectrometry: Used to find the relative molecular masses of organic compounds.
  • Mass spectrometry process:
    • compound is dissolved in solution, ionised by a high voltage supply (to mostly 1+ ions), accelerated by a negatively charged plate,
    • becomes a beam of ionised molecules, reach detector and cause a current to flow.
    • Time of flight used to work out m/z value and plot graph.
  • How does gas chromatography work and what does it tell you?
    • A stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so they are separated.
    • The amount of each compound can then be measured
  • Why do atoms and chemical bonds absorb infrared radiation?

    They are constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration
  • What effect do heavier atoms have on the frequency of vibration? Vibrate slower
  • What do the troughs on an infrared spectrum show? The frequencies where radiation has been absorbed - match to table to find out which bonds they represent
  • What is the fingerprint region?
    • Area of the infrared spectrum below wavenumber of 1500cm-1
    • Many peaks, caused by complex vibrations of the whole molecule.
    • Unique to every compound, so can be used to identify compounds
  • What does GCMS stand for? Gas chromatography linked to mass spectrometry
  • What effect does a stronger bond have on the frequency of vibration? Vibrate faster
  • How does infrared spectroscopy work?
    • Every bond has a unique vibration frequency in the infrared region of the EM spectrum
    • Bonds absorb radiation that has the same frequency as their frequency of vibration
    • Infrared radiation emerged from a sample is missing the frequencies that have been absorbed → this information can be used to identify the compound’s functional group
  • How do you test for aldehydes? What is the result?
    1. Warm with Fehling’s solution, result: brick red ppt forms (from blue solution)
    2. Warm with Tollens’ reagent, result: “silver mirror” (Ag(s) ppt) forms