Identification of an organic unknown

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A2 Chemistry – Assessed Practical: Skill P

Identification of an organic unknown

Aim

There are many different chemical tests, which enable us to identify an unknown compound. The only thing known about the compound is that it contains one of the following functional groups:

  • Alkene
  • Primary alcohol
  • Tertiary alcohol
  • Aldehyde
  • Ketone
  • Carboxylic acid
  • Ester
  • Phenol

I devised a sequence of tests that would identify which of the groups the sample contains. Initially I worked out what tests there are for each functional group, and decided which one to use on the basis that each test should be dependent on the result of the previous test, which helped me to arrange the sequence.

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Apparatus and reagents

  • Bromine Water
  • Test tubes/Test tube racks
  • Acidified Potassium Dichromate (VI) (K2Cr2O7)
  • 2, 4-Dinitrophenylhydrazine (2, 4-DNP)
  • 5% Aqueous Sodium hydrogen carbonate (NaHCO3)
  • Water Cooled condenser
  • Clamp and stand
  • 20 ml – 400 ml Beakers
  • Measuring Cylinder
  • Bunsen burner
  • Phosphorous Pentachloride (PCl5)
  • Ethanoic acid
  • Iron (III) Chloride (FeCl3)
  • Sodium metal (Na)
  • Tollens Reagent
  • Sulphuric Acid
  • Jones’s reagent (CrO3-H2SO4 in H2O)
  • Water bath
  • Bunsen burner/heating Mantle
  • 1 ml of 0.5 mols hydroxylamine hydrochloride
  • Sodium Hydroxide (NaOH)
  • Hydrochloric Acid (HCl)
  • Ethanol
  • Lucas reagent [ZnCl2 - conc. HCl]
  • ...

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