Alkenes (Edexcel AS Chemistry)

Exam Questions

48 mins4 questions

Medium

Hard

1a1 mark

This question is about alkenes.

Which of these has the molecular formula C₆H₁₀?

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1b1 mark

What is the systematic name of this alkene?

q2b-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

☐	A	2-methylpent-1-ene
☐	B	3-methylpent-1-ene
☐	C	2,3-dimethylbut-1-ene
☐	D	2,3-dimethylbut-3-ene

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1c3 marks

Two reactions of ethene are shown.

q2c-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

Complete the table.

Reaction	Reagent and condition	Product
1	HBr at room temperature
2

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3 marks

But-1-ene has the structure

q2d-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

Draw the structure of the polymer formed when but-1-ene polymerises.
Include two repeat units.

(1)

ii)

Calculate the number of molecules in 70.0 g of but-1-ene.
[Avogadro constant = 6.02 × 10²³ mol⁻¹]

(2)

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3a6 marks

This question concerns alkenes and some halogen compounds.

The alkene, propene, reacts with hydrogen chloride.

This reaction is best described as

(1)

☐	A	electrophilic substitution
☐	B	electrophilic addition
☐	C	nucleophilic substitution
☐	D	nucleophilic addition

ii)

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

1-chloropropane and 2-chloropropane are

(1)

☐	A	cis-trans isomers
☐	B	E/Z isomers
☐	C	structural isomers
☐	D	stereoisomers

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)

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3b4 marks

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

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)

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3c3 marks

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=CH₂

⇌

CH₂Cl–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)

☐	A	fractional distillation
☐	B	solvent extraction using a separating funnel
☐	C	heating under reflux
☐	D	bubble through dilute alkali

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1a1 mark

This question is about hydrocarbons.

Which of these molecular formulae represents a non-cyclic, saturated hydrocarbon?

☐	A	C₆H₆
☐	B	C₆H₁₀
☐	C	C₆H₁₂
☐	D	C₆H₁₄

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1b1 mark

How many structural isomers are there with the molecular formula C₅H₁₂?

☐	A	2
☐	B	3
☐	C	4
☐	D	5

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1c1 mark

How many σ bonds and π bonds are there in one molecule of cyclohexene?

q5c-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

		σ bonds	π bonds
☐	A	5	2
☐	B	6	1
☐	C	15	2
☐	D	16	1

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4 marks

When hydrocarbons undergo complete combustion, there is a change in the total volume of gases.

Ethane burns in excess oxygen.

2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O (g)

All gas volumes are measured at the same temperature and pressure when water is a gas.

What is the increase in the total volume when 100 cm³ of ethane is burned in excess oxygen?

(1)

☐	A	50 cm³
☐	B	100 cm³
☐	C	200 cm³
☐	D	500 cm³

ii)

A combustion experiment was carried out using conditions under which water was a liquid.

A cyclic hydrocarbon, C_xH_y , was mixed with excess oxygen and ignited.

Under the conditions of the experiment, this hydrocarbon was gaseous and had a volume of 25 cm³.

The equation for the complete combustion of C_xH_y is

C_xH_y(g) + (x + $\frac{y}{4}$ )O₂(g) → xCO₂(g) + $\frac{y}{2}$ H₂O (l)

The total gas volume decreased by 75 cm³.

The remaining gases were shaken with aqueous sodium hydroxide and the total gas volume decreased by a further 125 cm³.

All gas volumes were measured at the same temperature and pressure.

Suggest the identity of the cyclic hydrocarbon by calculating the molecular formula of C_xH_y .

Include the skeletal formula of the cyclic hydrocarbon.

(3)

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1e4 marks

Propene reacts with iodine monochloride, ICl, by an electrophilic addition mechanism.

Draw the mechanism for the reaction between propene and iodine monochloride to form the major product.

Include the dipole on the ICl molecule, curly arrows and any relevant lone pairs of electrons.

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4 marks

Limonene is obtained from the oil in lemon peel and it is the only alkene present.

q5f-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

0.500 g of the oil reacted with exactly 30.6 cm³ of a solution of bromine dissolved in cyclohexane with a concentration of 0.200 mol dm⁻³.

Calculate the percentage by mass of limonene in the oil.

Give your answer to an appropriate number of significant figures.

Assume that there is nothing else in the oil that reacts with bromine.

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☐	A	CH₃CH(OH)CH(CH₃)₂
☐	B	CH₂(OH)CH₂CH₂CH₂CH₃
☐	C	CH₃CH₂CH₂CH(OH)CH₃
☐	D	CH₃CH₂CH(OH)CH₂CH₃