Distinguishing between alkanes and alkenes

bromine water potassium manganate (vii)

1. Distinguishing between Alkanes and Alkenes

2. Test with Bromine Water How do we know halogens and alkenes undergo addition reactions? Bromine water turning colourless Test Observation Alkane Alkene Add a solution of bromine in water (bromine water) or in tetrachloromethane (CCl 4 ) under standard laboratory conditions The solution remains red-brown. Alkanes do not reaction with bromine water under standard laboratory conditions The solution changes from red-brown to colourless . The reaction is rapid. Alkenes undergo a rapid addition reaction with bromine solution under any conditions, including darkness

3. Testing alkenes – using bromine water

4. Test with acidified potassium manganate (vii) solution Test Observation Alkane Alkene Add acidified potassium manganate (vii) solution The solution remains purple. Alkanes do not reaction with acidified potassium manganate (vii) solution The solution changes from purple to colourless . The reaction is rapid. Alkenes rapidly reduce the purple MnO 4 ⁻ ion to the colourless Mn2+

5. Test with acidified potassium manganate (vii) solution

6. References Tindale, Ritchie et al, 2014, Chemistry for CSEC 2nd Edition , Nelson Thornes. Chapter 14, p 250 https://slideplayer.com/slide/3898949/