A LevelChemistryOCRExam Questions4. Core Organic ChemistryAlkanes

Alkanes (OCR A Level Chemistry A): Exam Questions

Exam code: H432

3 hours40 questions

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Alkanes

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1
1 mark

Which organic compound has the lowest boiling point?

  • 2,3,4-trimethylpentane

  • 2,3-dimethylhexane

  • 2-methylheptane

  • Octane

Choose your answer

2
1 mark

In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products.

Which compound could be present in the mixture of products?

  • CH3CH2CH2CH2CH3

  • CH3CH2CH2CH3

  • CH3CH2CH2Cl

  • CH3Cl

Choose your answer

3
1 mark

Ultraviolet light initiates the following reaction.

alkane + chlorine → chloroalkane + hydrogen chloride

What happens to chlorine in this photochemical reaction?

  • Heterolytic fission to give an electrophile

  • Homolytic fission to give an electrophile

  • Heterolytic fission to give a positive and negative ion

  • Homolytic fission to give free radicals

Choose your answer

4
1 mark

Which equation is correct for the complete combustion of heptane?

  • 2C7H16 + 22O2 → 14CO2 + 16H2O

  • 2C7H16 + 15O2 → 14CO + 16H2O

  • 2C7H14 + 21O2 → 14CO2 + 14H2O

  • 2C6H14 + 19O2 → 12CO2 + 14H2O

Choose your answer

5
1 mark

Ethane reacts with bromine in the presence of ultraviolet radiation via a radical substitution mechanism.

C2H6 + Br2 → C2H5Br + HBr

Which equation shows a termination step for this reaction?

  • C2H5● + Br2 → C2H5Br + Br●

  • C2H5● + Br• → C2H5Br 

  • Br2 → 2Br●

  • C2H6 + Br• → C2H5• + HBr

Choose your answer

6
1 mark

Which statement about methane is not correct?

  • It is a saturated hydrocarbon

  • It follows the general formula CnH2n

  • It has a tetrahedral shape

  • It can undergo free radical substitution

Choose your answer

7
1 mark

Give the bond angle present in methane. 

  • 90°

  • 107°

  • 109.5°

  • 120°

Choose your answer

8
1 mark

Which row shows possible products from the incomplete combustion of an alkane?

Carbon

Carbon monoxide

Hydrogen

A

✓

✓

×

B

✓

×

✓

C

×

✓

✓

D

✓

✓

✓

    Choose your answer

    9
    1 mark

    Which statement explains the trend in boiling points of alkanes as carbon-chain length increases?

    • Covalent bonds become stronger

    • Hydrogen bonds become stronger

    • Induced dipole–dipole interactions (London forces) become stronger

    • Permanent dipole–dipole interactions become stronger

    Choose your answer

    10
    1 mark

    Which statement(s) about propane is/are correct?

    1. It is non-polar.

    2. It cannot undergo incomplete combustion.

    3. It decolourises bromine.

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

    Choose your answer

    1
    1 mark

    Ethane reacts with bromine in the presence of ultraviolet radiation to form a mixture of organic products.

    Which equation shows a propagation step in the mechanism for this reaction?

    • C2H6 + Br• → C2H5Br + H•

    • C2H5• + Br• → C2H5Br

    • C2H5• + Br2 → C2H5Br + Br•

    • C2H5Br + H• → C2H5• + HBr

    Choose your answer

    2
    1 mark

    Isooctane (2,2,4-trimethylpentane) can be added to fuels for improved performance.

    Which is the correct equation for the complete combustion of isooctane?

    • C8H18 + 8½O2 → 8CO + 9H2O

    • C8H18 + 12½O2 → 8CO2 + 9H2O

    • C7H16 + 11O2 → 7CO2 + 8H2O

    • C8H18 + 13O2 → 8CO2 + 9H2O

    Choose your answer

    3
    1 mark

    1 mol of a compound reacts with 9.5 mol O2 for complete combustion.

    What is the formula of the compound?

    • C6H14

    • C6H13OH

    • C7H16

    • C7H15OH

    Choose your answer

    4
    1 mark

    Which property explains the low reactivity of alkanes?

    • High C–C bond enthalpy

    • High polarity of the C-H bond

    • Electron pair repulsion between σ-bonds

    • Free rotation about σ-bonds

    Choose your answer

    5
    1 mark

    Butane reacts with bromine in the presence of ultraviolet radiation to form 1-bromobutane.

    Which radical(s) is/are present in the mechanism for this reaction?

    1. CH3CH2CH2CH2•

    2. Br•

    3. H•

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

    Choose your answer

    6
    1 mark

    Propane reacts with chlorine in the presence of ultraviolet radiation.

    What is the overall equation for this reaction?

    • CH3CH=CH2 + Cl2 → CH3CHClCH2Cl

    • CH3CH2CH2• + Cl2 → CH3CH2CH2Cl + Cl•

    • CH3CH2CH2• + CH3CH2CH2• → CH3CH2CH2CH2CH2CH3

    • CH3CH2CH3 + Cl2 → CH3CH2CH2Cl + HCl

    Choose your answer

    7
    1 mark

    An alkane contains 38 hydrogen atoms per molecule.

    What is the empirical formula of the compound? 

    • C18H38

    • C19H38

    • C9H19

    • C9H18

    Choose your answer

    8
    1 mark

    The structure of 2-methylbutane is shown below.

    2-methylbutane skeletal formula with carbon atom X labelled

    What is the shape around the carbon atom labelled X?

    • Trigonal planar

    • V-shaped

    • Pyramidal 

    • Tetrahedral 

    Choose your answer

    9
    1 mark

    Which alkane has the highest boiling point?

    • CH3CH3

    • CH3CH2CH2CH3

    • CH3C(CH3)2C(CH3)2CH3

    • CH3(CH2 )6CH3

    Choose your answer

    10
    1 mark

    Which substance is not a product of the incomplete combustion of an alkane?

    • H2O

    • C

    • CO

    • SO2

    Choose your answer

    1
    1 mark

    Chlorine reacts with 1-chloropropane in the presence of ultraviolet radiation via a radical substitution mechanism.

    Which equation shows a propagation step in the mechanism for this reaction?

    • Cl2 → •Cl + •Cl

    • •Cl + •C3H6Cl → C3H6Cl2

    • C3H7Cl + •Cl → C3H6Cl2 + •H

    • •Cl + C3H7Cl → •C3H6Cl + HCl

    Choose your answer

    2
    1 mark

    Which sequence shows these compounds in order of increasing boiling point?

    • 2,4-dimethylheptane

    • Nonane

    • Octan-1-ol

    • Heptanoic acid

    • 2,4-dimethylheptane < nonane < octan-1-ol < heptanoic acid

    • 2,4-dimethylheptane < nonane < heptanoic acid < octan-1-ol

    • nonane < 2,4-dimethylheptane < octan-1-ol < heptanoic acid

    • octan-1-ol < heptanoic acid < 2,4-dimethylheptane < nonane

    Choose your answer

    3
    1 mark

    The CFC CCl2F2 can cause the breakdown of ozone in the upper atmosphere.

    Which statement(s) about this process is/are correct?

    1. •ClO + O → •Cl + O2 is a propagation step in the breakdown of ozone.

    2. The radicals produced from the initiation of this CFC are •Cl and •F.

    3. An equal concentration of •Cl and •F radicals are produced during initiation.

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

    Choose your answer

    4
    1 mark

    Chlorine reacts with fluoromethane to form trichlorofluoromethane.

    Which statement(s) is/are correct?

    1. The first propagation stage is CH3F + •Cl → •CH2F + HCl, followed by •CH2F + Cl2 → CH2ClF + •Cl.

    2. A termination step in this reaction will produce a product with the empirical formula CHCl2F.

    3. A limitation of this reaction is that further substitution occurs, leading to a mixture of organic products.

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

    Choose your answer

    5
    1 mark

    The equation for the incomplete combustion of heptane is shown below.

    C7H16 (g) + 8O2 (g) → 6CO (g) + CO2 (g) + 8H2O (g)

    Average bond enthalpies are given in the table.

    Bond

    Average bond enthalpy / kJ mol-1

    C–C

    348

    C–H

    414

    O=O

    498

    C=O (in CO2)

    804

    C≡O (in CO)

    1070

    O–H

    463

    What is the enthalpy change, in kJ mol-1, for this reaction?

    • +2740 kJ mol-1

    • -2740 kJ mol-1

    • +4474 kJ mol-1

    • -4474 kJ mol-1

    Choose your answer