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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Alkanes (OCR AS Chemistry)
Exam Questions
3 hours38 questions21 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?
- It is non-polar.
- It cannot undergo incomplete combustion.
- 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.
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?
- CH3CH2CH2CH2•
- Br•
- 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.
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.
In the upper atmosphere, the presence of Freon-12 can lead to ozone depletion.
Which of the following statements is/are correct?
- ClO• + O3 → Cl• +2O2 is one of the propagation steps in the depletion of the ozone layer.
- The free radicals produced from this CFC are Cl• and F•.
- 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?
- The first propagation step is CH3F + Cl• → •CH2F + HCl followed by
•CH2F + Cl2 → CH2ClF + Cl•. - A termination step in this reaction will produce a product with an empirical formula of CHCl2F.
- 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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