OCR A Level Chemistry

Topic Questions

4.5 Haloalkanes

11 mark

Which reaction is an example of nucleophilic substitution?

  • CH3CH2Br → CH2=CH2 + HBr

  • CH2=CH2 + HBr → CH3CH2Br

  • C3H7Br + NH3 → C3H7NH2 + HBr

  • C2H6 + Br2 → C2H5Br + HBr

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21 mark

What is the correct IUPAC name and classification of the following molecule?

q9-3-3-easy-mcq-halogenoalkanes

 

IUPAC name

Classification

A

1,bromopentane

Primary

B

2-bromopentane

Secondary 

C

2-bromopentane

Primary

D

4-bromopentane

Secondary

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31 mark

Which of the following statements is not correct about the depletion of the ozone layer?

  • CFCs produce free radicals when they are exposed to UV light in the upper atmosphere

  • 2 moles of ozone break down to form 3 moles of oxygen

  • Fluorine and chlorine free radicals can break down ozone molecules in the upper atmosphere

  • This is an example of a free radical substitution reaction

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41 mark

Three different halogenoalkanes are heated separately with aqueous silver nitrate, each reaction produced a precipitate.

Which halogenoalkane will produce a precipitate the fastest?

  • 1-iodopropane

  • They precipitate at the same rate

  • 1-chloropropane

  • 1-bromopropane

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51 mark

What is meant by a nucleophile?

  • Electron pair donor 

  • Electron pair acceptor 

  • Proton donor

  • Proton acceptor

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61 mark

Which compound has the fastest rate of reaction with potassium hydroxide and ethanol to form an alcohol?

  • 1- chlorobutane

  • 1-bromobutane

  • 1-fluorobutane

  • 1-iodobutane

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71 mark

Which statement is not correct about ozone?

  • It decomposes to form oxygen

  • Ozone holes are regions of the upper atmosphere where there is a reduced concentration of ozone

  • Hydrofluorocarbons are more damaging to the ozone layer than chlorofluorocarbons

  • It absorbs ultraviolet radiation from the Sun

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81 mark

The equation for the hydrolysis of 1-iodopropane is shown below 

CH3CH2CH2I + OH →CH3CH2CH2OH + I

What is the name of the mechanism used for this reaction? 

  • Electrophilic Addition

  • Oxidation

  • Elimination

  • Nucleophilic substitution 

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91 mark

CFCs contribute to ozone depletion in the upper atmosphere. 

One CFC has the formula CF2Cl2

What is the shape of a CF2Cl2 molecule and the F-C-Cl bond angle?

  Shape F-C-Cl bond angle
A pyramidal 107°
B tetrahedral 109.5°
C trigonal planar 120°
D linear 180°

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101 mark

Why are haloalkanes more reactive than alkanes?

  • The carbon-halogen bond is non-polar

  • The carbon and halogen atoms have different electronegativities

  • Carbon–halogen bonds are stronger than carbon–hydrogen bonds

  • Carbon is more electronegative than the halogen

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11 mark

Which statements is/are correct about haloalkanes?

  1. Published bond energies may differ due to them being a mean average of a specific bond in a homologous series.
  2. Haloalkanes that contain a C-F bond are the least reactive because this bond has the largest bond energy.
  3. When mixed with acidified silver nitrate, the haloalkane that precipitates the slowest is a chloroalkane.
  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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21 mark

Which statements is/are correct?

  1. The OH- ion is a better nucleophile than water.
  2. During nucleophilic substitution, the carbon-halogen bond breaks homolytically forming a halide ion.
  3. Nucleophiles are ‘nucleus loving’ so are themselves positively charged.
  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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31 mark

Which statement is not correct about the reactions of haloalkanes?

  • Haloalkanes and alcohols both take part in dehydration reactions to produce alkenes

  • Haloalkanes are soluble in water due to the polar carbon-halogen bond.

  • The OH- nucleophile acts as a base in an elimination reaction.

  • Hot ethanolic NaOH is used to produce the nucleophile in a substitution reaction. 

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41 mark

Which statements is/are not correct about the depletion of the ozone layer?

  1. CH3F will produce a fluorine free radical and a CH3 free radical in the presence of UV light.
  2. CH2ClF is a common example of a hydrofluorocarbon used in refrigerators.
  3. Chlorofluorocarbons are preferred to hydrofluorocarbons because they cause less depletion of the ozone layer.
  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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51 mark

Which equation shows a propagation step in the depletion of the ozone layer by nitrogen oxide radicals?

  • NO• + •NO2 → N2O + O2

  • •NO2 + O3 → •NO + 2O2

  • N2 + O2 → •NO + •NO

  • •NO + O3 → NO2 + •O2

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11 mark

A chemist adds four drops of 1-chloropentane, 1-bromopentane and 1-iodopentane separately to three test-tubes containing 1.0 cm3 of aqueous silver nitrate at 60 °C. A hydrolysis reaction occurred. 

Which statement best explains why 1-iodopentane precipitates first and 1-chloropentane precipitates last? 

  • The bond polarity decreases from C-Cl to C-I

  • The electronegativity of the halogens decreases down the group

  • The bond enthalpy decreases from C-Cl to C-I

  • The ionisation energy of the halogens decreases from Cl to I

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21 mark

Which statement best describes the mechanism of the reaction between aqueous sodium hydroxide and 2-bromopropane?

  • Attack by a nucleophile on a carbocation

  • Attack by a nucleophile on a carbon atom with a partial positive charge

  • Homolytic bond fission and attack by a nucleophile on a carbocation

  • Homolytic bond fission and attack by an electrophile on a partial positive charge

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31 mark

In the hydrolysis of bromoethane by aqueous sodium hydroxide, what is the nature of the attacking species and of the leaving group?

  Attacking group Leaving group
A nucleophile nucleophile
B electrophile nucleophile
C nucleophile electrophile
D electrophile electrophile

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41 mark

Which reagents and conditions are required for the following reaction to take place?

CH3CH2CH2I → CH3CH2CH2OH

  • Heated under reflux, aqueous potassium cyanide

  • Heated under reflux, ethanol, potassium cyanide

  • Heated under reflux with aqueous sodium hydroxide 

  • Warm with a solution of ethanol 

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51 mark

Which pair of reactions shows the correct sequence of attack of CFC molecules with ozone?

  Reaction 1 Reaction 2
A F + O3 → FO + O2 FO + O3 → 2O2 + F
B Cl + O3 ClO + O2 ClO + O3 → 2O2 + Cl
C Cl + O3ClO + O2 ClO + O3 → 2O2 + Cl
D Cl + O3ClO + O2 ClO + O3 → 2O2 + Cl

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61 mark

What is the correct IUPAC name and classification of the following molecule?

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  IUPAC name Classification
A 2,methyl,2,bromobutane Tertiary 
B 3-methyl-3-bromobutane Secondary 
C 2-bromo-2-methylbutane Secondary
D 2-bromo-2-methylbutane Tertiary 

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71 mark

The presence of a halogen in an organic compound may be detected by warming the organic compound with aqueous sodium hydroxide and silver nitrate.

Which compound would be the quickest to produce a precipitate?

  • 1,2,3-trichlorobutane 

  • 1,2-dichloro-3-fluorobutane 

  • 1,2-difluoro-3-iodobutane 

  • 1-bromo-2-chloro-3-fluorobutane 

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81 mark

The breakdown of the ozone layer can be caused by NO radicals.

Which equation is a propagation step in the mechanism for this process?

  • NO2 + O → NO + O

  • NO + O3 → NO2 + O2

  • O3 + O → 2O2

  • NO + O2 → NO2 + O3

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91 mark

Dichlorodifluoromethane, CCl2F2, has been used in aerosol propellants and as a refrigerant. 

Which statement helps to explain why dichlorodifluoromethane is chemically inert?

  • The carbon-fluorine bond energy is large

  • The carbon-fluorine bond has a low polarity

  • Fluorine is highly electronegative

  • Fluorine compounds are non-flammable

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101 mark

Which compound will not react with nucleophiles?

  • CH3CH2CH2OH

  • CH2CH2CHO

  • CH3CH2CH2Cl

  • CH3CH2CH2CH3

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