CIE iGCSE Co-Ordinated Science C11.2 Naming organic compounds Exam Style Questions Paper 4
Question
Ethane and ethene are members of two different homologous series. Fig. 11.1 shows the structure of ethene.
(a) Draw the structure of ethane.
▶️Answer/Explanation
The structure of ethane is:
H H
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H-C-C-H
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H H
Ethane is a saturated hydrocarbon with the molecular formula C2H6. It consists of two carbon atoms single-bonded to each other, with each carbon atom bonded to three hydrogen atoms.
(b) Ethene is a member of the homologous series called the alkenes. The alkenes are all hydrocarbons. State two other features that the alkenes in the homologous series have in common.
▶️Answer/Explanation
Two other features that alkenes in the homologous series have in common are:
- They contain at least one carbon-carbon double bond (C=C).
- They have the general formula CnH2n.
Alkenes are unsaturated hydrocarbons, meaning they have fewer hydrogen atoms compared to alkanes with the same number of carbon atoms due to the presence of the double bond.
(c) Ethene undergoes an addition reaction with steam. Fig. 11.2 shows the equation for the reaction. Complete the equation, by drawing the structure of the compound formed.
▶️Answer/Explanation
The structure of the compound formed when ethene reacts with steam is ethanol:
H H
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H-C-C-OH
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H H
Ethene (C2H4) reacts with steam (H2O) in the presence of a catalyst to form ethanol (C2H5OH). This is an example of an addition reaction where the double bond in ethene is broken, and a hydroxyl group (-OH) is added to one of the carbon atoms.
(d) Propene is another alkene. Fig. 11.3 shows the structure of propene.
The polymer poly(propene) can be made from propene. Complete the structure of poly(propene) in Fig. 11.4. Include all the atoms and bonds of the repeating unit.
▶️Answer/Explanation
The repeating unit of poly(propene) is:
H H
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-C-C-
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CH3 H
Poly(propene) is formed through the polymerization of propene (C3H6). The double bond in propene breaks, and the monomers link together to form a long chain polymer. The repeating unit has a methyl group (CH3) attached to every other carbon atom in the chain.
(e) Poly(propene) is made from propene in an addition polymerisation reaction. Polyesters are a group of polymers made in a condensation polymerisation reaction. Describe the differences between addition polymerisation and condensation polymerisation.
▶️Answer/Explanation
The differences between addition polymerisation and condensation polymerisation are:
- Addition Polymerisation: Involves the joining of monomers with double or triple bonds (e.g., alkenes) to form a polymer without the loss of any small molecules. The polymer formed has the same empirical formula as the monomer.
- Condensation Polymerisation: Involves the joining of monomers with the loss of small molecules such as water or methanol. The polymer formed has a different empirical formula from the monomers.
For example, in addition polymerisation, ethene monomers join to form polyethene, while in condensation polymerisation, a dicarboxylic acid and a diol react to form a polyester, releasing water as a byproduct.