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ASChemistryOCRExam Questions4. Core Organic Chemistry4.5 Haloalkanes

Haloalkanes (OCR AS Chemistry)

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4.5 Haloalkanes

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4.5 Haloalkanes

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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

      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● + O3 → ClO● + O2 ClO● + O3 → 2O2 + Cl●
        D Cl● + O3 → ClO + O2 ClO + O3 → 2O2 + Cl●

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          61 mark

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

          08e25b77-f8a8-449a-b0a5-5f6621afe673

            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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            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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