Pearson Edexcel IAL Chemistry AS Topic 5: Alkenes

[Maximum number: 2]

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

(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

[ 1 ]

(b)

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

A

3

B

4

C

10

D

11

[ 1 ]

[Maximum number: 8]

This question is about alkenes.

(a)

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

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

[ 2 ]

(i)

Explain why X can exist as geometric isomers.

[ 2 ]

(b)

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

[ 1 ]

(i)

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

[ 1 ]

determination of ratio between moles of
$\alpha$ -bisabolene: moles of hydrogen and hence number of
C=C bonds

Example of calculation

0.080992 / 0.02701=2.9986, so 3 C=C bonds

Allow TE from c(i) and c(ii) but must be nearest whole number

Do not award non integer answers

(c)

The repeat unit of the polymer polyisoprene is shown.

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

polyisoprene

[ 3 ]

(i)

Draw the skeletal formula of the monomer of polyisoprene.

[ 1 ]

(ii)

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

[ 2 ]

(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 ]

An answer that makes reference to the following points:

- solid calcium hydroxide is basic and neutralises/reacts with/absorbs acidic waste gases such as $\ce{HCl}$ , $\ce{SO2}$ , NOx or $\ce{CO2}$

- fine powder has a large surface area, ensuring a fast reaction / increasing the rate of reaction

[Maximum number: 6]

This question is about fuels and polymers. Used coffee grounds have been suggested as a carbon-neutral fuel to replace some fossil fuels.

(a)

Long chain alkanes are converted into smaller, more useful molecules including alkenes.

[ 2 ]

(i)

Give a test for alkenes, including the positive result.

[ 2 ]

bromine water / bromine solution / $\mathrm{Br}_{2}(\mathrm{aq})$ (1)

- yellow / orange / (red-)brown to colourless

(1)

MP2 is dependent on a correct reagent for MP1

Allow bromine / liquid bromine Ignore heat

Do not award "in UV light"

Do not award iodine

Allow decolourises or "turns colourless"

Accept:

$\mathrm{KMnO}_{4}$ with acid / $\mathbf{H}^{+}$ scores 1 mark purple to colourless scores 1 mark (allow decolourises)

Allow

$\mathrm{KMnO}_{4}$ with alkali / $\mathbf{O H}^{-}$ scores 1 mark purple → green scores 1 mark

(b)

Alkenes, such as ethene, can be used to make polymers.

[ 3 ]

(i)

Write a balanced equation for the polymerisation of ethene using displayed formulae.

[ 1 ]

displayed equation for the polymerisation of ethene

Figure for Answer to Question (i) — Edexcel A-Level Chemistry AS

Accept $90^{\circ}$ bond angles for the monomer

Allow letters other than n if used on both sides

Allow square brackets around the polymer

Ignore brackets around the monomer

Ignore any names even if incorrect

Do not award answers where

- the polymer does not have brackets

- the polymer continuation bonds do not pass through the brackets

(ii)

Bananas produce ethene as they ripen. Suggest one advantage and one disadvantage of using ripening bananas as a source of ethene for polymer production. (2)

[ 2 ]

(c)

Burning poly(chloroethene) in an incinerator results in the formation of hydrogen chloride.

[ 1 ]

(i)

Suggest how the hydrogen chloride could be removed from the waste gases produced in an incinerator. (1)

[ 1 ]

use of basic/alkaline (scrubbers) / form a ppt/salt/solid

or

injection of powdered activated carbon (to the flue)

or

pass through water / dissolve the HCl in water

Allow named examples of basic/alkaline chemicals e.g. $\mathrm{NH}_{3}, \mathrm{NaOH}, \mathrm{CaCO}_{3}$ etc

Scrubbers alone is insufficient

Accept adsorption in granular activated carbon or coke beds

Allow dissolve in steam

Ignore fractional distillation of gases

Do not award general descriptions of recycling

[Maximum number: 1]

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

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

A

3

B

4

C

10

D

11

[Maximum number: 2]

This question is about alkenes.

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

Figure for Question 5 — Edexcel A-Level Chemistry AS

Explain why X can exist as geometric isomers.

[Maximum number: 1]

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

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

A

Figure for Question 6 — Edexcel A-Level Chemistry AS — Option A

B

Figure for Question 6 — Edexcel A-Level Chemistry AS — Option B

C

Figure for Question 6 — Edexcel A-Level Chemistry AS — Option C

D

Figure for Question 6 — Edexcel A-Level Chemistry AS — Option D

[Maximum number: 1]

This question is about alkenes.

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

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

determination of ratio between moles of
$\alpha$ -bisabolene: moles of hydrogen and hence number of
C=C bonds

Example of calculation

0.080992 / 0.02701=2.9986, so 3 C=C bonds

Allow TE from c(i) and c(ii) but must be nearest whole number

Do not award non integer answers

[Maximum number: 2]

This question is about fuels and polymers. Used coffee grounds have been suggested as a carbon-neutral fuel to replace some fossil fuels.

Long chain alkanes are converted into smaller, more useful molecules including alkenes.

Give a test for alkenes, including the positive result.

bromine water / bromine solution / $\mathrm{Br}_{2}(\mathrm{aq})$ (1)

- yellow / orange / (red-)brown to colourless

(1)

MP2 is dependent on a correct reagent for MP1

Allow bromine / liquid bromine Ignore heat

Do not award "in UV light"

Do not award iodine

Allow decolourises or "turns colourless"

Accept:

$\mathrm{KMnO}_{4}$ with acid / $\mathbf{H}^{+}$ scores 1 mark purple to colourless scores 1 mark (allow decolourises)

Allow

$\mathrm{KMnO}_{4}$ with alkali / $\mathbf{O H}^{-}$ scores 1 mark purple → green scores 1 mark

[Maximum number: 2]

This question is about 2-Chloropropane.

Figure for Question 9 — Edexcel A-Level Chemistry AS

2-Chloropropane can also be produced from the reaction of propene with hydrogen chloride.

Explain why only a small amount of 1-chloropropane is produced in this reaction.

[Maximum number: 2]

This question is about alkenes.

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.

An answer that makes reference to the following points:

- solid calcium hydroxide is basic and neutralises/reacts with/absorbs acidic waste gases such as $\ce{HCl}$ , $\ce{SO2}$ , NOx or $\ce{CO2}$

- fine powder has a large surface area, ensuring a fast reaction / increasing the rate of reaction

Edexcel A-Level Chemistry AS 5 Alkenes Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question (a)

Question (b)

Question 2

Question (a)

Question (i)

Question (b)

Question (i)

Question (c)

Question (i)

Question (ii)

Question (d)

Question 3

Question (a)

Question (i)

Question (b)

Question (i)

Question (ii)

Question (c)

Question (i)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10