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Edexcel A-Level Chemistry AS 5 Alkenes Questions

Practise alkene formulae, C=C bonding, E-Z isomerism, addition reactions, mechanisms, polymerisation and polymer waste decisions.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • interpret alkene structures to count σ and π bonds, formulae and unsaturation
  • apply E-Z rules using priority groups and restricted rotation about the C=C bond
  • predict products, reagents and mechanisms for hydrogenation, hydration and halogen addition

Covered syllabus points

5.1—The general formula of alkenes and understand that alkenes and cycloalkenes are hydrocarbons which are unsaturated (have5.2—Geometric isomerism in terms of restricted rotation around a C=C double bond and the nature of the substituents on5.3—The E–Z naming system for geometric isomers and why it is necessary to use this when the cis- and trans- naming system5.4—The reactions of alkenes5.5—The qualitative test for a C=C double bond using bromine or bromine water5.6—The mechanism (including diagrams), giving evidence where possible, of: i the electrophilic addition of bromine and hydrogen5.7—The addition polymerisation of alkenes and draw the repeat unit given the monomer, and vice versa5.8—How chemists limit the problems caused by polymer disposal by: i developing biodegradable polymers ii removing toxic waste

Question 1

[Maximum number: 2]

Geometric isomerism is shown by 2-chlorobut-2-ene.

Question (a)

(a)

What is the skeletal formula of E-2-chlorobut-2-ene?

A
Figure for Question (a) — Edexcel A-Level Chemistry AS — Option A
B
Figure for Question (a) — Edexcel A-Level Chemistry AS — Option B
C
Figure for Question (a) — Edexcel A-Level Chemistry AS — Option C
D
Figure for Question (a) — Edexcel A-Level Chemistry AS — Option D
A

Structure A

B

Structure B

C

Structure C

D

Structure D

[ 1 ]

Question (b)

(b)

What is the total number of sigma bonds in Z-2-chlorobut-2-ene?

A

3

B

4

C

10

D

11

[ 1 ]

Question 2

[Maximum number: 8]

This question is about alkenes.

Question (a)

(a)

A straight-chain alkene, X, has the structure shown.

Figure for Question (a) — Edexcel A-Level Chemistry AS
[ 2 ]

Question (i)

(i)

Explain why X can exist as geometric isomers.

[ 2 ]

Question (b)

(b)

Bisabolenes are a group of compounds found in plants and fungi. Bisabolene molecules contain several carbon-carbon double bonds.
5.51 g of α\alpha-bisabolene reacted with 1873 cm31873 \mathrm{~cm}^{3} of hydrogen gas, H2\mathrm{H}_{2}. The reaction occured at a temperature of 150∘C150^{\circ} \mathrm{C} and a pressure of 152000 Pa .
[Mr\left[M_{\mathrm{r}}\right. value: α\quad \alpha-bisabolene =204.0]\left.=204.0\right]

[ 1 ]

Question (i)

(i)

Deduce the number of carbon-carbon double bonds in a molecule of α\alpha-bisabolene, using your answers to (c)(i) and (c)(ii).

[ 1 ]

Question (c)

(c)

The repeat unit of the polymer polyisoprene is shown.

Figure for Question (c) — Edexcel A-Level Chemistry AS

polyisoprene

[ 3 ]

Question (i)

(i)

Draw the skeletal formula of the monomer of polyisoprene.

[ 1 ]

Question (ii)

(ii)

A sample of polyisoprene has a relative molecular mass of 50250 . Calculate the number of repeat units in the sample.

[ 2 ]

Question (d)

(d)

Incinerators used to dispose of polymer waste have a system to remove waste gases.

Suggest why these systems contain solid calcium hydroxide and why it is finely powdered.

[ 2 ]
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