Alkenes (Edexcel AS Chemistry): Exam Questions

This question is about alkenes with the molecular formula C₅H₁₀ .

Draw the skeletal formulae of three branched chain alkenes with the molecular formula C₅H₁₀ .

Which of these compounds would form pent-2-ene only, when reacted with concentrated phosphoric acid, H₃PO₄?

Pent-2-ene reacts with hydrogen bromide, HBr, to form two bromoalkanes.

Complete the diagram to show the mechanism for the formation of 2-bromopentane in this reaction. Include curly arrows, and relevant lone pairs and dipoles.

A sample of pent-1-ene, with a mass of 1.33 g, is warmed to 60°C in a sealed container. The volume of the container is 500 cm³

Calculate the pressure inside the container. Include units and give your answer to an appropriate number of significant figures.

[Gas constant (R) = 8.31 J mol⁻¹ K⁻¹]

This question concerns alkenes and some halogen compounds.

The alkene, propene, reacts with hydrogen chloride. 

i) This reaction is best described as

(1)

ii) The reaction of propene with hydrogen chloride can produce two isomeric products:

 1-chloropropane and 2-chloropropane are

(1)

iii) Draw the mechanism for the reaction of propene with hydrogen chloride to produce 2-chloropropane. Include curly arrows, and any relevant dipoles and lone pairs.

 (4)

The halogenoalkane chloroethene is used to make the important polymer poly(chloroethene), PVC. 

i) Draw a displayed formula of two repeat units of poly(chloroethene).

(1)

 ii) Some polymers are disposed of by incineration. Ignoring any economic considerations, explain why incineration is not a suitable method for the disposal of poly(chloroethene).

(2)

 iii) Chloroethene has a boiling temperature of 260K and is known to be carcinogenic. Use these facts to state one precaution that chemists should take when using this compound.

(1)

Chloroethene can be manufactured by a two-stage process. 

i ) In stage 1, chlorine is reacted with ethene at a temperature between 50 °C and 80 °C

Cl₂ + CH₂=CH₂CH₂Cl–CH₂Cl   ΔH = −178 kJ mol⁻¹

Give one reason why a temperature below 50 °C and another reason, apart from costs, why a temperature above 80 °C would not be used for this process.

(2)

ii) In stage 2, the product from the first reaction is converted to chloroethene: 

CH₂Cl–CH₂Cl → CH₂=CHCl + HCl   ΔH = +71 kJ mol⁻¹ 

 Both products are required for use in other processes.

Which method would be most suitable for the separation of these two products?

(1)