Describe Tollens' test, Fehling's test and the iodoform test with equations. Use them to distinguish butanal from butanone, and butanone from pentan-3-one.

1. 1 · Say why the tests work. Aldehydes are easily oxidised; ketones are not. The iodoform test needs a CH₃CO- group.
2. 2 · Tollens' test. RCHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → RCOO⁻ + 2Ag + 2H₂O + 4NH₃: a silver mirror.
3. 3 · Fehling's test. RCHO + 2Cu²⁺ + 5OH⁻ → RCOO⁻ + Cu₂O + 3H₂O: a red-brown precipitate. Aromatic aldehydes do not respond.
4. 4 · Iodoform test. CH₃COCH₃ + 3I₂ + 4NaOH → CHI₃ + CH₃COONa + 3NaI + 3H₂O: a yellow precipitate.
5. 5 · Apply the tests. Butanal gives a silver mirror and red-brown Cu₂O; butanone gives neither. Butanone gives yellow CHI₃; pentan-3-one does not.
6. 6 · Link to real life. The aldehyde group of glucose reduces Fehling's solution, which was once used to test urine sugar.
7. 7 · Close in one line. So oxidation tests separate aldehydes from ketones, and the iodoform test finds methyl ketones.

Scoring tip: For every test write the reagent, what you do (warm or heat), and the colour or mirror you see, for both compounds of the pair.