1. Ethene gas decolourises bromine solution and potassium permanganate solution. But, ethane gas does not change the colour of these solutions.
2. Ethyne gas forms a white precipitate with ammonical solution of silver nitrate and red ppt. with ammonical solution of copper (I) chloride. But, ethane does not respond to such tests.
3.
S.No. | Test | Alkanes | Alkenes | Alkynes |
(i) | Bromine Test Add a few drops of sol. of bromine in carbon tetra-chloride to the hydrocarbon. | No change takes place. | The red colour of bromine is decolorised. | The red colour of bromine is decolorised. |
(ii) | Alkaline Potassium Permanganate Test: Add a few drops of alkaline pot. permanganate sol. To the hydrocarbon. | No change takes place. | The purple colour of Potassium permanganate is decolorised. | The purple colour of potassium permanganate is decolorised. |
(iii) | Ammoniacal Cuprous Chloride Test: Add a few drops of ammoniacal cuprous chloride sol. to thehydrocarbon. | No change takes place. | No change takes place. | A red ppt. of copper acetylide is formed. |