Nov02/Paper 2/Section A/Q4
Propane and propene are organic compounds.
(a) State one similarity and one difference between the structures of propane and propene.
(b) Name a substance that can be used to distinguish between propane and propene. In each case, describe what you would see.
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Answer:
(a) Similarity: Both Propane and Propene contain only hydrogen and carbon atoms covalently bonded together.
Difference: Propane belongs to the alkanes family and is a saturated compound with only single bonds between carbon atoms. Propene belongs to the alkenes family and has a double bond between the carbon atoms.
(b) Using Bromine water.
If you shake an alkene with bromine water (or bubble a gaseous alkene through bromine water), the solution becomes colourless. Alkenes decolourise bromine water.
Propane will not react with bromine water, while Propene will react with Bromine and be observed to decolourise Bromine water, turning it from reddish-brown to colourless. [This is due to Propene undergoing an addition reaction, with their double bonds opened up for Bromine to be added. Note that at higher level of chemistry you will then be required to list the products of such a reaction, and there are many possible products other than Bromo-propanes. But the important part is to know that Alkenes react with Halogens, resulting in their double bonds opened up and becoming saturated]
*Note. Part C is missing in this answer.
