ASChemistryOCRExam Questions4. Core Organic Chemistry4.2 Alkanes

Alkanes (OCR AS Chemistry)

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4.2 Alkanes

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4.2 Alkanes

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11 mark

Which organic compound has the lowest boiling point?

  • 2,3,4-trimethylpentane

  • 2,3-dimethylhexane

  • C. 2-methylheptane

  • Octane

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21 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

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31 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

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41 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

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51 mark

Ethane reacts with bromine in the presence of ultraviolet light to form bromoethane and hydrogen bromide.

C2H6 + Br2 → C2H5Br + HBr

Which equation represents the desired termination step for this reaction?

  • C2H5● + Br2 → C2H5Br + Br●

  • C2H5● + Br• → C2H5Br 

  • Br2 → 2Br●

  • 2C2H5● → C4H10

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61 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

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71 mark

Give the bond angle present in methane. 

  • 120°

  • 109.5°

  • 107°

  • 90°

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81 mark

Which of the following products are possible from the incomplete combustion of alkanes?

 

Carbon

Carbon monoxide

Hydrogen 

A

✔

✔

  

B

✔

  

✔

C

  

✔

✔

D

✔

✔

✔

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    91 mark

    As the size of the alkane increases, the boiling point also increases. 

    What intermolecular force explains this pattern?

    • Permanent dipole-dipole

    • Covalent bonding

    • Hydrogen bonding 

    • Induced dipole-dipole interactions

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    101 mark

    Which statements about propane are correct?

    1. It is non-polar.
    2. It cannot undergo incomplete combustion.
    3. It forms a colourless solution when reacted with bromine.

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

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    11 mark

    Which equation represents a valid propagation step in the free radical reaction between ethane and bromine?

    • C2H6 + Br• → C2H5Br + H•

    • C2H5• + Br• → C2H5Br

    • C2H5Br + Br• → C2H4Br• + HBr

    • C2H5Br + H• → C2H5• + HBr

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    21 mark

    Isooctane, shown below, can be added to fuels for improved performance.

    Isooctane

    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

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    31 mark

    1 mol of a compound reacts with 9.5 mol of O2 for complete combustion. What is the formula of the compound?

    • C6H14

    • C6H13OH

    • C7H16

    • C7H15OH

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    41 mark

    Which statement explains why alkanes can not react with halogens unless in the presence of UV light?

    • High bond enthalpy of the C-C bond 

    • High polarity of the C-H bond

    • Electron pair repulsion between σ-bonds

    • Free rotation about σ-bonds

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    51 mark

    Butane reacts with bromine in the presence of UV light to form 1-bromobutane.

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

    1. CH3CH2CH2CH2•
    2. Br•
    3. H•

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

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    61 mark

    What is the overall equation for the reaction between chlorine and propane in the presence of UV light? 

    • CH3CHCH2 + Cl2 → CH3CHClCH2Cl 

    • CH3CH2CH2• + Cl2 → CH3CH2CH2Cl + Cl•

    • CH3CH2CH2• + CH3CH2CH2• → CH3CH2CH2CH2CH2CH3

    • CH3CH2CH3 + Cl2 → CH3CH2CH2Cl + HCl 

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    71 mark

    An alkane contains 38 hydrogen atoms per molecule.

    What is the empirical formula of the compound? 

    • C18H38

    • C19H38

    • C9H19

    • C9H18

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    81 mark

    The structure of 2-methylbutane is shown below.

    ocr-as-4-2-mcq-m-q8-2-methylbutane

    What is the geometry around the carbon atom labelled X?

    • Trigonal planar

    • V-shaped

    • Pyramidal 

    • Tetrahedral 

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    91 mark

    Which of the following compounds has the highest boiling point? 

    • CH3C(CH3)2C(CH3)2CH3

    • CH3CH3

    • CH3CH2CH2CH3

    • CH3(CH2 )6CH3

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    101 mark

    Which of the following is not a product of incomplete combustion? 

    • H2O

    • C

    • CO

    • SO2

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    11 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

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    21 mark

    A student is supplied with five organic compounds:

    • Q = nonane
    • R = 2,4-dimethylheptane
    • S = octan-1-ol
    • T = heptanoic acid
    • U = nonan-3-ol

    The student plans to test the boiling point of these compounds.

    Which row shows the organic compounds in order of increasing boiling point?

    • R < Q < S < U < T

    • Q < R < U < S < T

    • T < S < U < Q < R

    • Q < R < T < S < U

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    31 mark

    Freon-12 is a CFC with the molecular formula CCl2F2.

    ocr-as-4-2h-mcq-q3-cfc

    In the upper atmosphere, the presence of Freon-12 can lead to ozone depletion.

    Which of the following statements is/are correct?

    1. ClO• + O3 → Cl• +2O2 is one of the propagation steps in the depletion of the ozone layer.
    2. The free radicals produced from this CFC are Cl• and F•.
    3. An equal concentration of Cl• and F• free radicals are produced from this CFC

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

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    41 mark

    Chlorine and fluoromethane can be used to make trichlorofluoromethane.

    Which of the following statements is/are correct?

    1. The first propagation step is CH3F + Cl• → •CH2F + HCl followed by
                         •CH2F + Cl2 → CH2ClF + Cl•.
    2. A termination step in this reaction will produce a product with an empirical formula of CHCl2F.
    3. A limitation of this reaction is that further substitution occurs leading to an impure product.

    • 1, 2 and 3

    • Only 1 and 2

    • Only 2 and 3

    • Only 1

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    51 mark

    What is the enthalpy change for the incomplete combustion of heptane that produces one mole of carbon dioxide but no particulate carbon?

    Bond

    Bond enthalpy (kJ mol-1)

    C-C

    348

    C-H

    414

    O=O

    498

    C=O

    804

    C≡O

    1070

    O-H

    463

     

    • 2740 kJ mol-1

    • -2740 kJ mol-1

    • 4474 kJ mol-1

    • -4474 kJ mol-1

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