Organic Chemistry

9 marks · Hard

Answer all parts about homologous series and the environmental impact of polymers.

(a)

Describe what is meant by a homologous series and give two features that members of a homologous series have in common.

[2 marks]

(b)

The compounds below are all alkenes or alcohols. Use the general formulae to complete the table.

General formulae for alkenes and alcohols
Name	General formula	Molecular formula (for n = 4)
Butene
Butanol

[3 marks]

(c)

Poly(chloroethene), also known as PVC, is a commonly used addition polymer. State one problem associated with the disposal of PVC and explain why it is not easily broken down in the environment.

[2 marks]

(d)

Describe two environmental impacts that can arise from burning PVC in incinerators.

[2 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) A homologous series is a group of organic compounds with the same functional group and similar chemical properties, in which each member differs from the next by a CH2 unit. Any two features: same general formula, similar chemical properties, gradual variation in physical properties, same functional group.

(b) — · must show General formulae: Alkenes - CnH2n; Alcohols - CnH2n+2O, Molecular formulae for n=4: Butene - C4H8; Butanol - C4H10O

(c) PVC is not biodegradable because its polymer chains are very unreactive (inert) and cannot be broken down by bacteria. This makes disposal difficult and leads to accumulation in landfill.

(d) Burning PVC produces toxic gases such as hydrogen chloride and carbon monoxide; it can also produce greenhouse gases such as carbon dioxide, contributing to pollution and global warming.

Show mark scheme and worked solution

Marking points

A1 (a) · 1 mark · Homologous series correctly described

A2 (a) · 1 mark · Two features listed (any two from: same general formula, same functional group, similar chemical properties, gradual changes in physical properties, differ by CH2)

B1 (b) · 1 mark · Correct general formula for butene (CnH2n)

B2 (b) · 1 mark · Correct general formula for butanol (CnH2n+2O)

B3 (b) · 1 mark · Correct molecular formulae for both for n=4: C4H8 (butene), C4H10O (butanol)

C1 (c) · 1 mark · States a problem with PVC disposal (e.g. non-biodegradable, accumulates in landfill)

C2 (c) · 1 mark · Explains why PVC is not easily broken down (e.g. strong covalent/inert polymer chains)

D1 (d) · 1 mark · States first environmental impact of burning PVC (e.g. toxic gases/hydrogen chloride/CO)

D2 (d) · 1 mark · States second environmental impact (e.g. CO2/greenhouse gas/global warming)

Worked solution

a) A homologous series is a family of organic compounds with the same functional group and similar chemical properties, in which each member differs from the next by a CH2 group. Features: (1) same general formula, (2) similar chemical properties, (3) same functional group, (4) gradual changes in boiling/melting point.

b) Table completed:

Name	General formula	Molecular formula (for n=4)
Butene	CnH2n	C4H8
Butanol	CnH2n+2O	C4H10O

c) PVC is not biodegradable (does not break down in the environment) due to strong inert covalent bonds in the polymer chains, so it accumulates in landfill.

d) Burning PVC releases toxic gases, such as hydrogen chloride (HCl) and carbon monoxide (CO), which can cause air pollution and acid rain. It also releases carbon dioxide (CO2), a greenhouse gas, contributing to global warming.