Alkenes

5 marks · Easy

This question is about the structure and properties of small alkenes.

(a)

Draw the displayed formula of propene.

[1 mark]

(b)

State whether butene is a gas, liquid or solid at room temperature.

[1 mark]

(c)

Describe the trend in boiling points as the number of carbon atoms increases from ethene to butene.

[2 marks]

(d)

Name the homologous series to which these alkenes belong.

[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.

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(a) — · must show C=C double bond in displayed formula, Correct hydrogen count

(b) Gas · must show gas

(c) The boiling point increases as the number of carbon atoms increases from ethene to butene, but all remain low and are gases up to C4. · must show boiling point rises with carbon number, all are gases up to butene

(d) Alkenes · must show alkenes

Also accept: Accept any correct drawn formula for propene showing C=C.

Common mistakes: Drawing a saturated compound instead of an alkene.; Confusing gases and liquids for small alkenes.

Show mark scheme and worked solution

Marking points

A1 (a) · 1 mark · Displayed formula of propene with double bond and correct number of H atoms.

B1 (b) · 1 mark · Correctly states that butene is a gas at room temperature.

C1 (c) · 1 mark · States that the boiling point increases as the number of carbon atoms increases.

C2 (c) · 1 mark · Recognises that all alkenes up to C4 are gases at room temperature.

D1 (d) · 1 mark · Correctly names the homologous series: alkenes.

Worked solution

a) Displayed formula of propene:

b) Butene is a gas at room temperature.

c) As the number of carbon atoms increases from ethene to butene, the boiling point increases, but all these alkenes are gases at room temperature.

d) These alkenes belong to the homologous series called alkenes.