Alkenes: Nomenclature, Preparation, properties and uses

CONTENT

• Nomenclature
• Preparation, Properties and Uses.

UNSATURATED HYDROCARBONS

These are hydrocarbons in which carbon atoms join with each other by multiple bonds.  The multiple bonds can be double bonds e.gAlkenes or triple bonds e.gAlkynes.

NOMENCLATURE

The process of naming in alkenes is obtained by substituting “ane” in alkane with ‘ene’ e.g Ethane changes to Ethene, propane to propene

LABORATORY PREPARATION

Ethene is prepared by heating ethanol with excess concentrated tetraoxosulphate(VI) acid at 170^o 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)  + H₂SO_4(aq)         →        C₂H₅HSO_4(aq) + H₂O_(l)

            C₂H₅HSO_4(aq)       →        C₂H_4(g)  + H₂SO₄.

PHYSICAL PROPERTIES

1.       Ethene is a colourless gas with faint sweetish smell.

2.      It is sparingly soluble in water.

3.      It is slightly less dense than air.

4.      It has no action on litmus paper.

Evaluation

1. How would you prepare a jar of ethene gas in the laboratory?
2. Mention four physical properties of Ethene.

USES OF ETHENE: Ethene is used

1. In the manufacture of plastics.
2. In making synthetic rubber.
3. To hasten the ripening of fruits.
4. In the production of other organic compounds e.g halo-alkane, ethane and ethanol.

GENERAL Evaluation/REVISION

1. Write balanced equations to show the reaction of ethene with the following:
2. Bromine water
3. Chlorine water
4. Acidified KMnO₄
5. State four uses of ethene.
6. Why is an empty flask inserted between the flat bottom flask and the conical flask holding the drying agent in the laboratory preparation of ethene?
7. State THREE factors that determine the spontaneity of a chemical reaction.
8. 0.92g of ethanol raised the temperature of 100g of water from 298K to 312.3K when

burned completely. What is the heat of combustion of ethanol?

READING ASSIGNMENT

New School Chemistry for Senior Secondary School by O.Y. Ababio (6^thedition) Pages 532-535

SECTION B

1.     Write and name the geometric isomers of compound with the molecular formula C₅H₁₀

2.     Write balanced chemical equation to show how ethene reacts with the following:

a. concentrated H₂SO₄b. bromine water c. acidified KMnO₄