Describe the colour change you would observe when an alkene is oxidised with acidified potassium manganate(VII).

When an alkene is oxidized with acidified potassium manganate(VII), you would observe a color change. Here are the steps:

1. Start with an alkene, which is a hydrocarbon with a carbon-carbon double bond.
2. Add acidified potassium manganate(VII) to the alkene. The acidified solution contains potassium manganate(VII) (KMnO4) dissolved in an acidic medium.
3. Initially, the potassium manganate(VII) solution is purple in color.
4. As the reaction proceeds, the purple color of the potassium manganate(VII) solution starts to fade.
5. The alkene undergoes oxidation, and the carbon-carbon double bond is broken.
6. The purple color of the potassium manganate(VII) solution is replaced by a brown precipitate called manganese dioxide (MnO2).
7. The brown precipitate indicates the completion of the oxidation reaction.
8. The alkene is converted into a diol, which is a compound with two hydroxyl groups (-OH) attached to adjacent carbon atoms.
9. The overall color change observed is from purple to brown.

In summary, the color change observed when an alkene is oxidized with acidified potassium manganate(VII) is from purple to brown, indicating the formation of manganese dioxide as a result of the oxidation reaction.