Chemistry Exp. To Oxidise Phenylmethanol – Flashcards

Oxidising phenylmethanol using potassium permanganate solution in the *presence of sodium carbonate*

3C₆H₅CH₂OH + 4KMnO₄ (purple) → 3C₆H₅COOH + 4MnO₂(brown) + H₂O + 4KOH

Phenylmethanol = known mass/vol. Potassium permanganate = saturated Sodium carbonate = solution In conical flask, in boiling water bath

To ensure sufficient is present to oxidise all of the phenylmethanol

Ensures pH stays at an alkaline level, as this oxidation reaction works best in alkaline conditions

Conical flask taken out of water bath when brown, run under tap to cool. Placed in fume cupboard, HCl added Dip glass rod in solution, then on litmus paper to make sure environment is acidic Sodium sulphite solution added until brown precipitate disappears Placed in ice Crystals formed filtered in Buchner flask Conical flask rinsed out with solution in Buchner Crystals washed with ice-cold water Crystals left dry overnight Weight taken

To convert the intermediate compound sodium benzoate to benzoic acid

Benzoic acid is only slightly soluble in cold water, causes benzoic acid to be precipitated out

Neutralises any excess sodium carbonate added and potassium hydroxide produced in reaction Provides an acidic medium for Mn⁴⁺ ions to be reduced Mn⁴⁺ + 2e⁻ → Mn²⁺ (in the presence of H⁺)

Na₂SO₃

Reducing agent; Reduces Mn⁴⁺ + 2e⁻ → Mn²⁺ Mn⁴⁺ is insoluble, and would contaminate the benzoic acid, so reduced to Mn²⁺ which is soluble

SO₃²⁻ + H₂O → SO₄²⁻ + 2H⁺ + 2e⁻ (provides electrons and protons, I think)

Benzoic acid low solubility in water => maximise yield of crstals

Dries crystals Speeds up filtration process

To get rid of any remaining crystals

Remove any soluble impurities