These are hydrocarbons in which carbon atoms join with each other by multiple bonds. The multiple bond can be double bonds e.g Alkene or triple bonds e.g Alkyne.
- Ethene2 .Ethyne
H – C = C – H H – C = C – H
The process of naming in alkene is obtained by substitute “ane” in alkane with ‘ene’ e.g Ethane changes to Ethene, propane to prepene
PREPARATION (Lab. Preparation)
- Ethene is prepared by heating ethanol with excess concentrated tetraososulphate VI acid at 170o C. The acid acts as a dehydrating agent by removing water from the ethanol . Thus the process is called dehydration.
The reaction occurs in two stages
C2H5OH(aq) + H2SO4 (aq) C2H5HSO4 + H2O
C2H5HSO4 C2H4+ H2SO4.
The overall reaction is represented by the equation .
C2H5OH H2SO4 C2H4+ H2SO4
- Ethene can be prepared through cracking of Alkane e.g C3H8 C2H4 + CH4.
- By dehydration
e.g H H Cl H H
H – C – C – H C = C + HCL
H Cl H H
- Ethene is a colourless gas with faint sweetish odour .
- It is sparingly soluble in water
- It is slightly less dense than air
- It has no action on litmus paper
- Write four (4) physical properties of Ethene
- How would you prepare a jar of ethane gas in the laboratory?
Ethene undergoes combustion/oxidation in air or in the presence of oxygen and produce carbon(iv)oxide and steam .
C2H4 + 3O2 2CO2 + 2H2O.
- Additional reaction
- With hydrogen known as hydrogenation
H H H H
H- C= C – H + H2 H – C – C – H
Ethene H H Ethane
- With halogen know as halogenation
H H HH
H – C = C- H + Cl2 H C – C – H
Ethene ClCl 1,2- dichloroethane
- With Halides known as hydrogenation
e.g H- C = C – H + HBr H H
H HH C C – H
ethene H Br 1-Bromoethane.
- With acidified /Alkaline KMnO4 known as hydroxylation. It decolourses acidified KMnO4, but turns alkaline KMnO4 to green and result to ethane -1,2- diol.
H – C = C – H + KMnO4 H – C – C – H
H H HH
- With Hydrogen peroxide in the presence of osmium trioxde to form ethan -1,2- diol.
H – C = C + H + H2O2 H – C – C – H
Ethane -1,2- diol.
- With conc. H2SO4 known as hydration to produce fuming liquid of ethyl hydrogen sulphate.C2H4 + H2SO4 C2H5HSO4
When ethyl hydrogen sulphate is hydrolyzed, tetraoxosulphate (vi) acid and ethanol are produced.C2H5SO4 C2H5OH + H2SO4
- Ethene gas decolourizes bromine water to produce bromoethanol.
H – C = C – H + HBrO H – C – C – H
H H (radiation brown) Br OH
H-C = C – H + HClO H – C – C – H
- Polymerization of ethane to produce polythene.
C = CC – C – C – C
- With ozone known as ozomolysis to from etheneozomides.
e.g H H O
C = C + O3 H2C CH2
H H O
- Ethene can also undergo additional reaction with oxygen in the presence of silver catalyst at about250oC to form epoxy ethane.
H H HH
H – C = C – H + ½ O2 H – C – C – H
- Used in the manufacture of plastics.
- Used in making synthetic rubber.
- Used to hasten the ripening of fruits.
- Used in the production of other organic compounds e.g halo-alkane,ethane, ethanol.
- Describe the reaction of ethane with the following:
- Bromine water
- Chlorine water
- Acidified KMnO4
- State four (4) uses of Ethene.
- The name of the organic compound with the structure below:
C = C
- Cis- but-2-ene
- Trans –cis-but-2-ene
- Trans-1-2- but-2-ene
- 1,2- dimethyl ethane.
- In the reaction given below:
C2H5OH Conc H2SO4 C2 H4Conc H2SO4is acting as
- oxidizing agent B reducing agent C. Dehydrating agent D. Drying agent.
- One of the following is not a chemical property of ethane.
(a ) Polymerization (b) Substitutional (c ) Hydration (d) Addition.
- Function of the empty bottle during the preparation of ethane gas is
(a) to remove oxygen (b) to remove CO2 ( c) to prevent sucking back of the gas (d) None of the above.
- Additional reaction of hydrogen and ethene is known as
(a) polymerization (b) additional (c) combustion (d) hydrogenation
- Describe two (2) methods of obtaining ethene industrially.
2a. Write and name the geometric isomers of compound with the molecular formular C5H10
- With chemical equation only, show how ethane reacts with the following:
– alkaline KMnO4
– Conc. H2SO4