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ASChemistryCIEExam Questions15. Halogen Compounds15.1 Halogenoalkanes

Halogenoalkanes (CIE AS Chemistry)

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15.1 Halogenoalkanes

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15.1 Halogenoalkanes

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11 mark

X and Y are the reagents required to convert 1-bromopropane into butanoic acid.

3-3-cie-ial-chemistry-diagram-q1easy

What are the correct identities of X and Y?

 

X

Y

A

B

C

D

NH3

KCN in C2H5OH

KCN in C2H5OH

HCN

HCl (aq)

NaOH (aq)

HCl (aq)

NaOH (aq)

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    21 mark

    Which reaction occurs when ethane and chlorine are mixed in diffused sunlight?

    • A free-radical substitution with hydrogen given off.

    • A free-radical substitution with hydrogen chloride given off.

    • A free-radical substitution with no gas given off.

    • A nucleophilic substitution with hydrogen chloride given off.

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    31 mark

    Chlorofluoroalkanes, CFCs, can be used as refrigerants, aerosol propellants and fire extinguishers.

    CFCs such as CCl3F and CCl2F2 are more stable than chloroalkanes such as CCl4.

    What is the reason for their greater stability?

    • Fluorine has a higher first ionisation energy than chlorine.

    • Fluorine radicals are more stable than chlorine radicals.

    • The C–F bond energy is larger than the C–Cl bond energy.

    • The C–F bond is more polar than the C–Cl bond.

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    41 mark

    Light initiates the following reaction.

    alkane + chlorine rightwards arrow 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 free radical.

    • Homolytic fission to give a free radical.

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    51 mark

    High-energy irradiation in the stratosphere produces radicals from chlorofluoroalkanes, commonly known as CFCs.

    Which radical could result from this irradiation of CHFClCF2Cl?

    • CHFClC•FCl

    • •CHClCF2Cl

    • •CHFCF2Cl

    • •CFClCF2Cl

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    61 mark

    Which reaction is an example of nucleophilic substitution?

    • CH3CH2Br rightwards arrow CH2=CH2 + HBr

    • CH2=CH2 + HBr rightwards arrow CH3CH2Br

    • C3H7Br + H2O rightwards arrow C3H7OH + HBr

    • C2H6 + Br2 rightwards arrow C2H5Br + HBr

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    71 mark

    Bromomethane, CH3Br, is used as a fumigant to destroy insect pests in grain that is to be stored. It can be made by reacting methanol with hydrogen bromide.

    CH3OH  +  HBr  rightwards arrow  CH3Br  + H2O

    What type of reaction is this?

    • Condensation

    • Electrophilic substitution

    • Free radical substitution

    • Nucleophilic substitution

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    81 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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    91 mark

    The reaction of chlorine with methane is carried out in the presence of light.

    What is the function of the light?

    • To break the C–H bonds in methane.

    • To break up the chlorine molecules into radicals.

    • To break up the chlorine molecules into ions.

    • To heat up the mixture.

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    11 mark

    Four drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane were put separately into three test-tubes containing 1.0 cm3 of aqueous silver nitrate at 60 °C.

    A hydrolysis reaction occurred. 

    R represents the butane chain C4H9– and X the halogen atom.

    H2O (l) + R–X (l) + Ag+ (aq) rightwards arrow R–OH (aq) + AgX (s) + H+ (aq)

    The rate of formation of cloudiness in the tubes was in the order RCl < RBr < RI

    Why is this?

    • The R–X bond polarity decreases from RCl to RI.

    • The solubility of AgX (s) decreases from AgCl to AgI.

    • The ionisation energy of the halogen decreases from Cl to I.

    • The bond energy of R–X decreases from RCl to RI.

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    21 mark

    What is involved in the mechanism of the reaction between aqueous sodium hydroxide and 1-bromobutane?

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

    • Heterolytic bond fission and attack by a nucleophile on a carbocation.

    • Homolytic bond fission and attack by an electrophile on a carbanion.

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

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    31 mark

    A reaction between chlorine and propane in ultraviolet light produces two isomeric monochloropropanes, C3H7Cl, as products.

    Which information about this reaction is correct?

     

    Type of bond fission in initiation step

    Expected ratio of 1-chloropropane to 2-chloropropane produced

    A

    B

    C

    D

    Heterolytic 

    Heterolytic

    Homolytic

    Homolytic

    1:1

    3:1

    1:1

    3:1

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      41 mark

      Bromine and propene undergo an addition reaction.

      Which is a property of the product?

      • It exists in cis-trans isomers.

      • It is more volatile than propene

      • It possesses a chiral centre.

      • It possesses hydrogen bonding.

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      51 mark

      Which compound undergoes an SN1 substitution reaction?

      • CH3CH2CH2Br

      • (CH3)3CCH2I

      • 3-3-m-6

      • CH2=CHCl

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      61 mark

      Under the Montreal Protocol, the manufacture of chlorofluorocarbons has been phased out, and they are being replaced by fluorocarbons.

      One chlorofluorocarbon which was widely used as a solvent is CCl2FCClF2. Large stocks of it remain. One process to use up these stocks is to convert it into the fluorocarbon CH2FCF3 by the following route.

      u42czm3Q_3-3-m-7

      What type of reaction is step 2?

      • Electrophilic substitution

      • Free radical reduction

      • Isomerisation

      • Nucleophilic substitution

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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 silver nitrate.

      Which compound would be the quickest to produce a precipitate?

      • 3-3-m-8a

      • 3-3-m-8b

      • 3-3-m-8c

      • 3-3-m-8d

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      81 mark

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

       

      Attacking group

      Leaving group

      A

      B

      C

      D

      Electrophile

      Electrophile

      Nucleophile

      Nucleophile

      Electrophile

      Nucleophile

      Electrophile

      Nucleophile

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        91 mark

        Which reaction will give 2-chloropropane in the best yield?

        • Propane gas with chlorine gas in the presence of ultraviolet light

        • Propan-2-ol with dilute NaCl (aq)

        • Propan-2-ol with SOCl2

        • Propene with dilute HCl (aq)

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        101 mark

        Aqueous sodium hydroxide reacts with 1-bromopropane to give propan-1-ol.

        How should the first step in the mechanism be described?

        • By a curly arrow from a lone pair on the OH– ion to the Cδ+ atom of 1-bromopropane.

        • By a curly arrow from the Cδ+ atom of 1-bromopropane to the OH– ion.

        • By a curly arrow from the C–Br bond to the C atom.

        • By the homolytic fission of the C–Br bond.

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        11 mark

        When an isomer Y of molecular formula C4H9Br undergoes hydrolysis in aqueous alkali to form  an alcohol C4H9OH, the rate of reaction is found to be unaffected by changes in the concentration of OH– ions present.

        Which is the most likely molecular structure of Y?

        • CH3CH2CH2CH2Br

        • CH3CH2CHBrCH3

        • (CH3)2CHCH2Br

        • (CH3)3CBr

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        21 mark

        A tertiary bromoalkene, indicated here by      C–Br, reacts with aqueous NaOH. The mechanism has the reaction pathway below.

        3-3-cie-ial-chemistry-diagram-q4hard

        Which point in the diagram is correctly identified?

        • 3-3-h-4a

        • 3-3-h-4b

        • 3-3-h-4c

        • 3-3-h-4e

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        31 mark

        When a solution of potassium cyanide in ethanol is heated under reflux with 1-chloropropane, what is the organic product of the reaction called?

        • Butanenitrile

        • 1-chloropropanenitrile

        • Ethanenitrile

        • Propanenitrile

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        41 mark

        The compound 2-ethyl-3-methylbutanoic acid is used as a flavouring in some food.

        3-3-h-6Which compound will produce 2-ethyl-3-methylbutanoic acid when heated under reflux with sodium cyanide in ethanol, followed by acid hydrolysis of the reaction product?

        • 3-3-h-6a

        • 3-3-h-6b

        • 3-3-h-6c

        • 3-3-h-6d

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        51 mark

        When phenacyl chloride, C6H5COCH2Cl, is reacted with aqueous NaOH, the substitution reaction follows an SN2 mechanism.

        Which structure represents a species formed during the reaction?

        • 3-3-h-7a

        • 3-3-h-7b

        • 3-3-h-7c

        • 3-3-h-7d

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        61 mark

        Coniine is the major constituent of the poison ‘oil of hemlock’.

        3-3-h-8Coniine can be synthesised by reacting ammonia with a dibromo compound, X.

                                       NH3 + C8H16Br2 rightwards arrow coniine + 2HBr

                                                         X

        What is the name of compound X?

        • 1,1-dibromo-2-propylcyclopentane

        • 1,2-dibromo-2-propylcyclopentane

        • 1,4-dibromooctane

        • 1,5-dibromooctane

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        71 mark

        A reaction pathway diagram is shown.

        3-3-h-9Which reaction does not have such a profile?

        • CH3CHO + HCN  rightwards arrow with NaCN on top  CH3CH(OH)CN

        • C2H5Br + NaOH rightwards arrow C2H5OH + NaBr

        • (CH3)3CBr + NaOH rightwards arrow (CH3)3COH + NaBr

        • 3-3-h-9a

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        81 mark

        Which of the following molecules will have no permanent dipole?

        • CCl2F2

        • CHCl3

        • C2Cl4

        • C2H5Cl

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