What other reaction is commonly used as a functional group test for alkenes?
There are two common tests for alkenes.
Bromine in CCl₄
Add a few drops of the Br₂/CCl₄ solution to the unknownd.
If your unknown is an alkene, the reddish-brown colour of the bromine will disappear quickly.
CH₂=CH₂ + Br₂ → BrCH₂-CH₂Br
The video below shows the colour change.
The Baeyer Test
Shake a few drops of a dilute solution of aqueous potassium permanganate with a small amount of the unknown.
If your compound is an alkene, the purple colour of the permanganate ion will disappear and a brown precipitate of MnO₂ will form:
3CH₂=CH₂ + 2KMnO₄ + 4H₂O → 3HOCH₂-CH₂OH + 2MnO₂(s) +2KOH
The video below shows the colour changes for a positive test.