Chemistry 2010 JAMB Past Questions - Question 49: Two hydrocarbons X and Y were treated with bromine water. X decolorised the solution and Y did not. Which class of compound does Y belong?

Correct Answer

D

Explanation

The compound that does not decolorize bromine water is: **Alkanes**

**Explanation:**

- Alkenes (C=C) have a double bond between carbon atoms, which is more reactive than the single bonds in alkanes (C-C).
- Bromine water is an oxidizing agent, and the double bond in alkenes readily reacts with bromine, decolorizing the solution.
- Alkanes, on the other hand, do not have such reactive double bonds, so they do not react with bromine water and do not decolorize the solution.

Here is a table summarizing the reactivity of different hydrocarbons with bromine water:

| Hydrocarbon | Functional group | Reacts with bromine water? |
|---|---|---|
| Alkene | C=C | Yes |
| Alkyne | C≡C | Yes |
| Aromatic | Benzene ring | No |
| Alkane | C-C | No |

As you can see, only alkenes and alkynes have functional groups that are reactive enough to decolorize bromine water. Alkanes and aromatic compounds, like benzene, do not react with bromine water.