Edexcel A-Level Chemistry AS 4 Introductory Organic Chemistry and Alkanes Questions

Identify the functional group and longest chain, apply locants and formula conventions and use the stated reagent or hazard evidence to classify the reaction or decision.

Exam points

Name and draw organic compounds using longest chains, locants and functional groups.
Convert among molecular, empirical, structural and displayed formulae accurately.
Apply hazard and reaction evidence to alkane practicals and reaction terminology.

Covered syllabus points

4.1—The difference between hazard and risk 4.2—The hazards associated with organic compounds and why it is necessary to carry out risk assessments when dealing 4.3—Suggest ways in which risks can be reduced and reactions carried out safely, for example: i working on a smaller scale ii 4.4—The concepts of homologous series and functional group 4.5—Apply the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature to: i name compounds relevant 4.6—Classify reactions as addition, substitution, oxidation, reduction or polymerisation 4.7—Bond breaking can be: i homolytic, to produce free radicals ii heterolytic, to produce ions 4.8—Definitions of the terms ‘free radical’ and ‘electrophile’ 4B: Alkanes Students will be assessed on their ability to:4.9—The general formula of alkanes and cycloalkanes, and understand that they are hydrocarbons (compounds of carbon and hydrogen 4.10—The term ‘structural isomerism’4.11—Draw and name the structural isomers of alkanes and cycloalkanes with up to six carbon atoms 4.12—Alkanes are used as fuels and obtained from the fractional distillation, cracking and reforming of crude oil 4.13—Pollutants 4.14—The problems arising from pollutants from the combustion of alkane fuels 4.15—Discuss the reasons for developing alternative fuels in terms of sustainability and reducing emissions 4.16—Apply the concept of carbon neutrality to different fuels, such as petrol, bioethanol and hydrogen 4.17—The reactions of alkanes with: i oxygen in the air (combustion) ii halogens 4.18—The mechanism of the free radical substitution reaction between an alkane and a halogen: i using free radicals, which are

[Maximum number: 1]

When carrying out chemical experiments, the hazards and risks must be considered.
For a given chemical

the hazard is fixed but the risk varies

the hazard varies but the risk is fixed

both hazard and risk are fixed

both hazard and risk vary

[Maximum number: 1]

Which hazard warning symbol would be found on a bottle of hexane?

Figure for Question 2 — Edexcel A-Level Chemistry AS

hazard symbol A

hazard symbol B

hazard symbol C

hazard symbol D

[Maximum number: 4]

This question is about ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

(a)

Ethene and chlorine react to form 1,2-dichloroethane.

[ 2 ]

(i)

One hazard symbol for 1,2-dichloroethane is shown.

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

By identifying this hazard, give one way of minimising the risk when working with 1,2-dichloroethane in a laboratory.

Assume the use of safety goggles and a laboratory coat.

[ 2 ]

(b)

Ethene reacts with buta-1,3-diene to form cyclohexene as the only product.

Complete the equation for the formation of cyclohexene from ethene and buta-1,3-diene using skeletal formulae.

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

[ 1 ]

(c)

Two reactions of cyclohexene are shown.

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

[ 1 ]

(i)

Classify the type of reaction occurring in Reaction 1.

[ 1 ]

[Maximum number: 2]

This question is about ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

Ethene and chlorine react to form 1,2-dichloroethane.

One hazard symbol for 1,2-dichloroethane is shown.

Figure for Question 4 — Edexcel A-Level Chemistry AS

By identifying this hazard, give one way of minimising the risk when working with 1,2-dichloroethane in a laboratory.

Assume the use of safety goggles and a laboratory coat.

[Maximum number: 3]

This question is about the hormone testosterone, the structure of which is shown.

Functional group 1 Functional group 2

Give the name of each of the three circled functional groups.

Functional group 1
Functional group 2
Functional group 3

[Maximum number: 2]

Terpenes and terpenoids are groups of chemicals found in plants.
They contribute to the smell and taste of the plant, and so are used in flavourings and perfumes.

Both terpenes and terpenoids have carbon skeletons based on one or more units of the compound isoprene.

Figure for Question 6 — Edexcel A-Level Chemistry AS

isoprene
Terpenes are made up of two or more isoprene units joined together, while terpenoids have additional functional groups, often containing oxygen.

Limonene and myrcene are both terpenes composed of two isoprene units.
Menthol, linalool and citronellol are terpenoids containing an - OH group.

(a)

Give the IUPAC name for isoprene.

[ 1 ]

(b)

Give the IUPAC name of the product formed by complete hydrogenation of myrcene.

[ 1 ]

[Maximum number: 1]

This question is about ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

Two reactions of cyclohexene are shown.

Figure for Question 7 — Edexcel A-Level Chemistry AS

Classify the type of reaction occurring in Reaction 1.

[Maximum number: 2]

This question is about 2-Chloropropane.

Figure for Question 8 — Edexcel A-Level Chemistry AS

2-Chloropropane can be produced by reacting propane with chlorine in a homolytic free radical reaction.

\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}+\mathrm{Cl}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{CHClCH}_{3}+\mathrm{HCl}

Using your answer to (b)(i), state what is meant by the terms homolytic and free radical.
homolytic
free radical

[Maximum number: 1]

An electrophile

accepts a pair of electrons

always has a negative charge

always has a positive charge

donates a pair of electrons

[Maximum number: 2]

This question is about cycloalkanes.

(a)

The skeletal formula of cycloalkane D is shown.

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

[ 1 ]

(i)

Give the molecular formula of D.

[ 1 ]

$\mathrm{C}_{7} \mathrm{H}_{14}$

Allow $\mathrm{H}_{14} \mathrm{C}_{7} / \mathrm{C} 7 \mathrm{H} 14 / \mathrm{H} 14 \mathrm{C} 7$

Ignore any other symbols as working

e.g. $\mathrm{CH}_{2} \mathrm{CHCH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHCH}_{3}$

Do not award superscripts e.g. $\mathrm{C}^{7} \mathrm{H}^{14}$

(1)

(ii)

Give the name of D.

[ 1 ]

(b)

A cycloalkane, E, has a molar mass of $126 \mathrm{~g} \mathrm{~mol}^{-1}$ .

Deduce the molecular formula of E.

[ 1 ]

( E is) $\mathrm{C}_{9} \mathrm{H}_{18}$

Allow $\mathrm{H}_{18} \mathrm{C}_{9}$

Allow large numbers

Ignore working

Do not award superscripts

(1)

(c)

There are four structural isomers of $\mathrm{C}_{6} \mathrm{H}_{12}$ with a ring of four carbon atoms.

One of these isomers is shown, in the first box.
Complete the skeletal formulae of the other three isomers.

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

[ 2 ]

All 3 correct

- Any 2 correct

(2)

(1)

Examples of isomers:

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

Allow isomers in any order

Allow $\mathrm{CH}_{3}$ and $\mathrm{C}_{2} \mathrm{H}_{5}$ for side chains

Ignore bond angles and bond lengths

Do not award any structure with 2 or more rings

(2)

[Maximum number: 4]

This question is about alkenes.

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

Figure for Question 11 — Edexcel A-Level Chemistry AS

Draw the skeletal formulae of the four structural isomers of X that are alkenes. Do not include geometric isomers.

[Maximum number: 1]

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.

Name this process.

[Maximum number: 1]

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 not normally used as fuels as they produce soot.

Name another pollutant formed by incomplete combustion of alkanes.

[Maximum number: 1]

Some diesel cars contain an extra catalytic converter for the reduction of nitrogen oxides $\left(\mathrm{NO}_{\mathrm{x}}\right)$ in exhaust gases.
A solution of urea is used for this process.

Figure for Question 14 — Edexcel A-Level Chemistry AS

urea

State why $\mathrm{NO}_{\mathrm{x}}$ emissions are harmful to the environment.

An answer that makes reference to the following point:

- (oxides of nitrogen lead to the formation of) acid rain

Allow formation of photochemical smog

Allow "NO can react with ozone"

Allow descriptions of acid rain formation e.g. forms $\mathrm{HNO}_{3}$

Do not award greenhouse effect / global warming

Do not award depletes the ozone layer without reference to nitrogen(II) oxide/NO

[Maximum number: 3]

Many cars use fuels containing ethanol as well as hydrocarbons. The E numbers of these fuels show the percentage by volume of ethanol in the fuel. For example, an E5 fuel contains 5% ethanol and 95% hydrocarbons by volume.

Many countries are gradually replacing E5 fuels with E10 fuels.

Explain how this change might result in a more sustainable fuel.

[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.

Explain why coffee grounds might be considered a carbon-neutral fuel. (2)

An explanation that makes reference to the following points:

- the carbon dioxide released when the fuel is used/burnt/combusted (is equal)

(1)

- (to the carbon dioxide that is) used/absorbed/taken in by the plant/during photosynthesis

(1)

Ignore answers relating to fuel burnt on transport affecting carbon neutrality / energy spent on processing and drying

MP1 do not award carbon for carbon dioxide

Marks are independent

Ignore sustainable resource

If no other marks awarded, for 1 mark:

Accept "no net $\ce{CO2}$ produced when using coffee grounds as a fuel"

Accept "carbon intake = carbon release"

Allow "renewable resource"

[Maximum number: 2]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question 17 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

The standard enthalpy change of combustion, $\Delta_{\mathrm{c}} H^{\ominus}$ , of 2,2,4-trimethylpentane is $-5461 \mathrm{~kJ} \mathrm{~mol}^{-1}$ .

Write the equation for the complete combustion of 2,2,4-trimethylpentane, using molecular formulae. State symbols are not required.

molecular formula for 2,2,4-trimethylpentane

- rest of equation correct conditional on use of $\mathrm{C}_{8} \mathrm{H}_{18}$ or use of structural / displayed / skeletal formula for 2,2,4-trimethylpentane

Example of equation:
$\mathrm{C}_{8} \mathrm{H}_{18}+12 \frac{1}{2} \mathrm{O}_{2} \rightarrow 8 \mathrm{CO}_{2}+9 \mathrm{H}_{2} \mathrm{O}$

Accept 25/2 for $12 \frac{1}{2}$

Allow multiples e.g. $2 \mathrm{C}_{8} \mathrm{H}_{18}+25 \mathrm{O}_{2} \rightarrow 16 \mathrm{CO}_{2}+18 \mathrm{H}_{2} \mathrm{O}$

Ignore state symbols even if incorrect

[Maximum number: 4]

(a)

Hexane will react with chlorine in the presence of ultraviolet light to form a number of products.

[ 4 ]

(i)

Describe the role of the ultraviolet light in the initiation step of this reaction.

[ 2 ]

(ii)

The alkane dodecane, $\mathrm{C}_{12} \mathrm{H}_{26}$ , is formed in this reaction.

Write equations for the propagation step and for the termination step for the formation of this product.
Use molecular formulae in your equations.
Propagation step

Termination step

[ 2 ]

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