Which of the following reagents can distinguish between propene and propane ?
(i) `Br_(2)//C Cl_(4)`
(ii) Conc. `H_(2)SO_(4)`
(iii) Dilute `KMnO_(4)` solution
(iv) `H_(2)//Pt`

Options

A. (i),(iii)
B. (i),(ii),(iii)
C. (i),(ii),(iii),(iv)
D. (ii),(iii)

Answer

C

Explanation

A positive test is indicated by one or more detectable events such as a color change, appearance of an insoluble liquid or solid, evolution of a gas, uptake of gas, or evolution of heat.
(i) Loss of color

(ii) Solubility in cold conc. sulphuric acid

(iii) Loss of color and formation of precipitate

(iv) Uptake of a gas
Whenever possible, we select for a characterization test a reaction that is repidly and conveniently carried out and that gives rise to an easilyobservable change. An alkene is best characterized by its property of decolorizing both a solution of `Br_(2)` in `C Cl_(4)` and a cold, dilute alkaline `KMnO_(4)` solution ( the Baeyer test). Both tests are easily carried out. In one, the red color disappears while in the other, the purple color disappears and is replaced by brown `MrO_(2)` precipitate.