Question

You find a container in the lab whose label is blurred. It definitely says "oct," but you can't determine if it is octane or octane. How could you distinguish between them using a chemical test? What are the results of those test with "octane" and "octane?"

Answer 1

It can be either octane or octene

If you draw the structures you will find a double bond in octene. But there is no double bond in octane. So since that is the only point of difference (i.e unsaturation in octene) we will test it. Octane is paraffin and gives very few tests but alkene (octene) shows many tests, it can be converted to many different functional groups( such as alcohol/carbonyl etc) and if product is formed we can confirm.

The easiest test is unsaturation test by using cold dilute KMnO4.

Alkanes are immune to this test, but alkenes decolourise the solution. This is known as Bayer's test. To perform this add a drop of cold dilute KMnO4.

KMnO4 + CHR=CHR + H2O -----> C(OH)HR-C(OH)HR MnO2 + 2OH-

OH groups gets attached to both sides of the alkene

Another test is the bromine water test, but bromine is a very poisonous substance so I prefer potassium permanganate over this. Anyways, bromine water gets decolourised when alkene is added to it.