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Alkanes

Set BExam practice

Name

Time 1 hour

Total 21 marks

A Data Booklet may be used.

Multiple choice

4 marks

CommonCH₄ and Cl₂ react together in the presence of ultraviolet light. Which statements are correct?

1Hydrogen gas is produced.2Bond breaking occurs only in the initiation step.3CH₃Cl is formed in the propagation and termination steps.

A3 only

B1 and 2 only

C2 and 3 only

D1, 2 and 3

Answer [1]

Source: 2022 HCI J1 Promo P1 Q18

1,1-dimethylcyclopentane undergoes free-radical substitution with limited bromine in the presence of ultraviolet light. A mixture of mono-brominated products is obtained.

Assuming that the reaction occurs at the same rate at every carbon atom, what is the total number of mono-brominated products (ignore stereoisomers) obtained?

Answer [1]

Source: 2022 HCI J1 Promo P1 Q19

Use of the Data Booklet is relevant to this question. Chlorofluorocarbons (CFCs) were widely used as refrigerants, solvents and propellants. However, the manufacture of CFCs has been phased out, as they undergo homolytic fission by ultraviolet radiation in the stratosphere, which contributes to ozone depletion. Which radical could result from the irradiation of CHFClCF₂Cl?

A•CHFCF₂Cl

B•CHClCF₂Cl

CCHFClĊFCl

D•CFClCF₂Cl

Answer [1]

Source: VJC 2012 Prelim P1 Q17, via EJC Alkanes Topical Revision, Q2

What are the products from the following reaction? ĊH₃ + CH₃CH₂Cl → ?

ACH₄ + CH₃ĊHCl

BCH₃CH₂ĊH₂ + HCl

CCH₃CH₂CH₃ + Cl•

DCH₃CH₂CH₂Cl + H•

Answer [1]

Source: DHS 2013 Prelim P1 Q13, via EJC Alkanes Topical Revision, Q6

Structured questions

17 marks

CommonCrude oil consists of a mixture of hydrocarbons, namely alkanes, cycloalkanes and various aromatic hydrocarbons.

(a)

Alkanes are generally unreactive. Suggest a possible reason why this is so.

[1]

(b)(i)

Butane, CH₃CH₂CH₂CH₃, can react with bromine gas to form 2-bromobutane under suitable conditions. Name and outline the mechanism for the formation of 2-bromobutane from butane.

[3]

(ii)

Suggest the ratio of 1-bromobutane to 2-bromobutane formed from the reaction between butane and bromine.

[1]

(iii)

2-bromobutane, , is a constitutional isomer of 2-bromo-2-methylpropane, . Using structure and bonding, predict and explain the relative boiling point of 2-bromo-2-methylpropane compared with 2-bromobutane.

[3]

Source: MJC 2018 Promo Section B Q1(a) and (b), via EJC Alkanes Topical Revision, Section B Q6

Octane has a total of 18 isomers. Isomers of octane may be distinguished by the number of mono-brominated products formed upon reaction with bromine under ultraviolet light. Draw an isomer of octane which reacts with limiting bromine to give

(a)

only one mono-brominated product

[1]

(b)

three mono-brominated products (ignore stereoisomers)

[1]

Source: RJC H2 Chemistry Tutorial 11 (Alkanes), Q7(b)(i)

CommonCatalytic converters containing solid platinum convert over 90% of carbon monoxide and gaseous nitrogen oxides into harmless gases such as CO₂ and N₂. Outline the mode of action of the platinum catalyst.

[2]

Source: 2024 JPJC J2 Prelim P2 Q2(a)

ChallengeIn the chlorination of propane, four products, A, B, C and D, of molecular formula C₃H₆Cl₂ were isolated. Each underwent further chlorination, and the number of trichloro-products (C₃H₅Cl₃) obtained from each was determined by gas chromatography. A gave one trichloro product, B gave two, and C and D each gave three. When optically active C was chlorinated, one of the trichloropropanes, E, obtained was optically active while the other two were inactive. Give the structural formulae of A, B, C, D and E.

[5]

Source: RJC H2 Chemistry Tutorial 11 (Alkanes), Q3