Organic Chemistry

9 marks · Hard

This question is about organic molecules and addition polymers.

(a)

Draw the structural formula and the displayed formula for the organic compound with the molecular formula C3H6.

(i)

Structural formula:

[1 mark]

(ii)

Displayed formula:

[1 mark]

(b)

Name the homologous series to which C3H6 belongs. State the general formula for this series.

(i)

Name of homologous series:

[1 mark]

(ii)

General formula:

[1 mark]

(c)

Poly(propene) is made by addition polymerisation of propene. Write a balanced chemical equation for the production of poly(propene) using displayed formulae for the monomer and the repeat unit of the polymer.

(i)

Displayed formula for the monomer:

[1 mark]

(ii)

Displayed formula for the repeat unit of the polymer (show continuation bonds at the ends):

[1 mark]

(iii)

Complete the balanced equation using your structures.

[1 mark]

(d)

State one use of poly(propene).

[1 mark]

(e)

Give one reason why addition polymers such as poly(propene) are difficult to dispose of.

[1 mark]

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(i)) CH2=CHCH3

(a(ii)) Displayed formula with double bond between first and second carbon, each carbon showing the correct number of hydrogens · must show C1 with two hydrogens, double bonded to C2, C2 single bonded to C3, C3 as CH3

(b(i)) Alkenes

(b(ii)) CnH2n

(c(i)) Displayed formula for propene: CH2=CHCH3 (with bonds shown)

(c(ii)) Displayed (repeat) unit for poly(propene): —[CH2—CH(CH3)]— with continuation bonds at each end · must show Correct links at each end

(c(iii)) n CH2=CHCH3 → [—CH2—CH(CH3)—]n · must show n on both sides

(d) Ropes OR crates OR plastic containers (any suitable use from content)

(e) They are non-biodegradable / very difficult to break down in the environment

Show mark scheme and worked solution

Marking points

A1 (a(i)) · 1 mark · Correct condensed structural formula for C3H6

A2 (a(ii)) · 1 mark · Correct displayed formula with placement of double bond and hydrogens

B1 (b(i)) · 1 mark · Correct homologous series identified as alkenes

B2 (b(ii)) · 1 mark · General formula of alkenes given as CnH2n

C1 (c(i)) · 1 mark · Correct displayed formula for propene monomer

C2 (c(ii)) · 1 mark · Correct displayed formula for polymer repeat unit with continuation bonds

C3 (c(iii)) · 1 mark · Correct balanced polymerisation equation using structures (follow-through)

D1 (d) · 1 mark · Any sound use for poly(propene)

E1 (e) · 1 mark · Reason for disposal problem; must refer to non-biodegradability/inertness

Worked solution

a(i) Structural formula: CH2=CHCH3

a(ii) Displayed formula:

b(i) C3H6 belongs to the homologous series of alkenes.

b(ii) The general formula for alkenes is CnH2n.

c(i) Displayed formula for the monomer (propene):

c(ii) Displayed formula for the repeat unit (with continuation bonds):

c(iii) Balanced equation:

d) Poly(propene) can be used to make ropes (or crates or plastic containers).

e) Poly(propene) is difficult to dispose of because it is non-biodegradable: it does not break down easily in the environment.