Question 3
(a) Consider the following compounds:
CH3CH=CHCH3; CH3COOCH2CH3; CH3(CH2)2CH3 and CH3CH(OH)CH2CH3
- State the family to which each organic compound belongs.
- Give the IUPAC name of each compound.
- Arrange the compounds in order of increasing boiling point.
Give reasons for your answer. [15 marks]
(b) Chloroethane can be prepared by reacting chlorine with ethane.
- State the experimental condition required for this reaction to occur.
- Write the equation for the initiation step.
- Write equations for the propagation steps of the reaction.
- Name the product formed at the termination step of the reaction [5 marks]
(c) Ethanol is produced on a large scale by heating ethane with steam.
- State two other conditions necessary for the reaction.
- Write the balanced chemical equation for the reaction.
- State one advantage of this method over the fermentation method. [5 marks]
Observation
This is an optional question, and the response of the candidates to the question was fair.
In part (a), majority of the candidates stated correctly the family to which each organic
compound belongs. However, only few of them could give the IUPAC name of each compound. They gave the names as butene instead of but-2-ene, but -2 – 01 instead of butan -2-01. Majority of the candidates could not arrange the compounds in order of increasing boiling points and therefore, could not give any reason for their answers.
In part (b), majority of the candidates stated experimental condition required for the reaction
to occur.
In part (c), most of the candidates that attempted the question could not state the two other
conditions necessary for producing ethanol by heating ethene with steam. Some candidates
wrote high temperature/low pressure.
The expected answers include:
(a) (i) CH3CH =CHCH3 – Alkene
CH3COOCH2CH3 – Alkyl alkanoate
CH3(CH2)2CH3 – Alkane
CH3CH(OH)CH2CH3 – Alkanol.
(ii) CH3CH=CHCH3 - But–2–ene / 2 – butane
CH3COOCH2CH3 - Ethyl ethanoate
CH3(CH2)CH3 - Butane
CH3CH(OH)CH2CH3 - Butan–2–o1
(iii) CH3(CH2)CH3< CH3CH = CHCH3< CH3COOCH2CH3
< CH3CH(OH)CH2CH3
The stronger the forces, the higher the boiling point
Vander waals forces exist in CH3CH=CHCH3 and CH3(CH2)2CH3
Dipole – dipole interaction exist in CH3COOCH2CH3
Hydrogen bonding exits in the alkanol.
[15 marks]
(b) (i) UltraViolet light / sunlight
[2 marks]
(c) (i) - High pressure
- Acid catalyst OR Conc. H2SO4/H3PO3
(ii) C2 H4 + H2SO4 C2 H5 HSO4
C2H5HSO4+H2O C2H5OH + H2SO4
OR
C2H4 + H2O CH3CH2OH
(iii)- Faster reaction
- Continuous reaction
- Pure production/concentrated product
- Does not produce CO2 or green house gas/environmentally friendly