Alkenes (CnH2n)

Question 1

Alkene production: with reagents, conditions and catalysts

Answer 1

1.Cracking of long chain hydrocarbons, conditions= Heat and Al2O3 catalyst.
2.Elimination of halogenoalkanes, condtions= NaOH(ethanol), will form Alkene+NaX+H2O.
3.Dehydration of alcohols, conditions= Hot Al2O3/Hot pumice/conc.H2SO4.

Question 2

Alkene reactions: with reagents, conditions and catalysts

Answer 2

1.Hydrogenation, conditions= Nickel/Platinum catalyst and 170°C, will form alkane.
2.Hydration, condtions= conc.H3PO4, 330°C and 60ATM/6000kPa, will form alcohol.
3.Addition of halogen, no conditions, will form halogenoalkane.
4.Addition of hydrogen halide, no condtions, will form halogenoalkane.
5.Mild oxidation with Cold dilute H+/KMnO4 (VII) to produce DIOL.
6.Oxidation with Hot concentrated H+/KMnO4 (VII) to produce H20 AND CO2/CARBOXYLIC ACID/KETONE.

Question 3

Oxidising agents and color change:

Answer 3

H+/KMnO4 (VII), Purple to colorless.
H+/K2Cr2O7 (VI), Orange to green.

Question 4

Test for alkenes:

Answer 4

Alkene + Br₂(aq) →Halogenoalkane in the absence (and presence) of UV light.
Brown to colourless.
Colour change can happen in absence (and the presence) of sunlight/UV light.