Organic Chemistry

8 marks · Normal

The displayed formulae of simple hydrocarbons can be used to understand their properties and uses.

(a)

Draw the displayed formula for but-1-ene.

[2 marks]

(b)

State the typical number of bonds formed by: (i) carbon (ii) hydrogen (iii) oxygen (iv) chlorine

[2 marks]

(c)

Fractional distillation of crude oil separates hydrocarbon molecules by their size. Explain why refinery gases rise to the top of the column while bitumen is collected at the bottom.

[2 marks]

(d)

State one common use for (i) refinery gas and (ii) bitumen.

[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) Displayed formula for but-1-ene with double bond between first and second carbons · must show Four carbons in chain, Double bond at position 1

(b) (i) 4; (ii) 1; (iii) 2; (iv) 1

(c) Refinery gases have small molecules with low boiling points, so they rise to the top as gases. Bitumen molecules are large with high boiling points, so they condense and remain as a liquid at the bottom. · must show Boiling point, Molecule size, Position in column

(d) Refinery gas: domestic heating/cooking; Bitumen: road making

Common mistakes: Incorrect placement of double bond in displayed formula; Mixing up number of bonds for each atom; Stating boiling point reasoning backwards

Show mark scheme and worked solution

Marking points

A1 (a) · 1 mark · Correct carbon skeleton with double bond at position 1 (between C1 and C2).

A2 (a) · 1 mark · All bonds and hydrogens shown correctly in the displayed formula.

B1 (b) · 2 marks · 1 mark each for correct number for carbon (4), hydrogen (1), oxygen (2), chlorine (1).

C1 (c) · 1 mark · States refinery gases have low boiling points/small molecules that rise.

C2 (c) · 1 mark · States bitumen has large molecules/high boiling point so stays at bottom.

D1 (d) · 1 mark · One correct use for refinery gas.

D2 (d) · 1 mark · One correct use for bitumen.

Worked solution

a) Displayed formula for but-1-ene: H2C=CH–CH2–CH3 (all bonds and hydrogens explicitly shown).

b) (i) carbon: 4 (ii) hydrogen: 1 (iii) oxygen: 2 (iv) chlorine: 1

c) Refinery gases have small molecules and low boiling points, so they stay as gases and rise to the top. Bitumen consists of very large molecules with high boiling points, so they condense and are collected at the bottom as a residue.

d) Refinery gas is used in domestic heating/cooking. Bitumen is used for road making (surfacing).