Lesson Notes By Weeks and Term - Senior Secondary School 2

SUBJECT: CHEMISTRY

CLASS:  SS 2

DATE:

TERM: 3rd TERM

REFERENCE MATERIALS

• New School Chemistry for Senior Secondary Schools by O. Y. Ababio
• New System Chemistry for Senior Secondary Schools by T. Y. Toon et al
• S.S.C.E  Past Questions and Answers on Chemistry 
• U.T.M.E Past Questions and Answers on Chemistry

 
WEEK SEVEN

TOPIC: ALKENES

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 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(aq) + H2O(l)

    C2H5HSO4(aq)               C2H4(g)  + H2SO4.

The overall reaction is represented by the equation

C2H5OH(aq)H2SO4C2H4(g)  + H2SO4(aq)

    -H2O 

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.

CHEMCIAL PROPERTIES

1. Combustion: Ethene undergoes combustion in air or in the presence of oxygen and produce carbon (IV) oxide and steam.

    C2H4(g) +  3O2(g)               2CO2(g)  + 2H2O(l)

2. Addition reaction: This is a reaction in which two molecules combine to form one molecule.  
3. Reaction with hydrogen (Hydrogenation):

        H    H            H        H

  H-C= C –   H   +  H2 H -   C  -     C – H                                                      

Ethene

    H         H          Ethane

1.   Reaction with halogens (Halogenation):

        H    H    HH

H  -  C =  C- H  +  Cl2                   H - C -  C -  H

        Ethene            ClCl      1,2- dichloroethane

1. Reaction with hydrogen halides(Halohydrogenation):

                        H    H

        H- C = C – H + HBr            H - C    C - H

        H    HH Br

        Ethene                      1-bromoethane.

1. Reaction with acidified /Alkaline KMnO4 (Hydroxylation):  It decolourises acidified KMnO4, but turns alkaline KMnO4 to green and ethane -1,2- diol is formed.

                            OH     OH

        H – C = C – H    +    KMnO4                       H -     C   -    C  - H

        H     H                                                           H        H

 Ethane-1,2-diol (glycol)

1.     Reaction with Hydrogen peroxide in the presence of osmium trioxde to form ethan -1,2- diol.

OH  OH

    H -    C  =  C - H + H2O2          H – C -  C  - H

        H      HHH

                    Ethane -1,2- diol.

1. Reaction with concentrated H2SO4produces a fuming liquid (ethyl hydrogen       sulphate)

        C2H4  + H2SO4               C2H5HSO4

When ethyl hydrogen sulphate is hydrolyzed, tetraoxosulphate (VI) acid and ethanol are produced.

        C2H5SO4    C2H5OH  + H2SO4

1.   Ethene gas decolourizes bromine water to produce bromoethanol.

                                    H      H               

    H – C = C – H+HBrO                H – C  –C -  H

        H   H( brown)                      Br    OH   

Bromoethanol

1. Polymerization of ethane to produce polythene.

                H      HHHH    H               

 C   =  C- C  - C  - C  -  C-

n      H       HHHHH    n

                                                                Polyethene

1.   Ethene can also undergo addition 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

O

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:

1. Bromine water
2. Chlorine water
3. Acidified KMnO4

1. State four uses of ethene.
2. 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?
3. State THREE factors that determine the spontaneity of a chemical reaction.
4. 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 (6thedition) Pages 532-535

WEEKEND ASSIGNMENT

SECTION A: Write the correct option ONLY

1. The name of the organic compound with the structure below is

        CH3        H

C  =  C

        H               CH3

1. Cis- but-2-eneB.Trans –cis-but-2-eneC.Trans-1-2- but-2-eneD.1,2- dimethyl ethane.
2. In the reaction given below:

    C2H5OH    Conc H2SO4       C2 H4Conc H2SO4is  acting as 

 -H2O

1. oxidizing agent B. reducing agent C. dehydrating agent    D. drying agent.
2. One of the following is not a chemical property of ethene.
3. Polymerization B. Substitution reaction C. Hydration D.  Addition reaction
4.   Function of the empty bottle during the preparation of ethane gas is 
5. to remove oxygen B. to remove CO2C. to prevent sucking back of the gas  D. None of the above
6.   Addition reaction of hydrogen and ethene is known as 
7. polymerization B. halogenation C. combustion D. hydrogenation  

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:
3. concentrated H2SO4b. bromine water c. acidified KMnO4