11 mark
Reagent X is used to convert 1-bromopropane into butanenitrile.
What is the correct identity of X?
Concentrated H2SO4
Ethanolic KCN
Aqueous KCN
Excess NH3
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Halogenoalkanes (AQA A Level Chemistry)
Exam Questions
4 hours45 questions21 mark
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 electronegativity than chlorine
Fluorine radicals are more stable than chlorine radicals
The C–F bond is stronger than the C–Cl bond
The C–F bond is more polar than the C–Cl bond
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31 mark
Ultraviolet light initiates the reaction between chlorine and methane.
CH4 + Cl2 → CH3Cl + HCl
What happens to the chlorine molecule in this reaction during the initiation step?
Heterolytic fission to give an electrophile
Heterolytic fission to give a free radical
Homolytic fission to give an electrophile
Homolytic fission to give a free radical
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41 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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51 mark
Methane and chlorine react in the presence of UV light.
Which of the following reactions is not a possible termination step?
CH3● + CH3● → CH3CH3
CH3● + Cl● → CH3Cl
Cl● + Cl● → Cl2
Cl2 + CH3● → CH3Cl + Cl●
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61 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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71 mark
What would be the main product of the reaction between 2-bromobutane and ethanolic potassium hydroxide, KOH, which is heated under reflux?
Butane
Butan-2-ol
But-2-ene
Butan-1-ol
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81 mark
Potassium cyanide will react with 1-chloropropane, CH3CH2CH2Cl, and form butanenitrile via a nucleophilic substitution reaction.
Which of the following descriptions of the mechanism steps are correct?
| First step | Second step |
A | Curly arrow from the lone pair on the CN- nucleophile to the δ+ carbon atom | Curly arrow from the C-Cl bond to the chlorine atom |
B | Curly arrow from the δ+ carbon atom to the CN- nucleophile | Curly arrow from the C-Cl bond to the carbon atom |
C | Curly arrow from the lone pair on the CN- nucleophile to the δ- carbon atom | Curly arrow from the C-Cl bond to the chlorine atom |
D | Curly arrow from the δ- carbon atom to the CN- nucleophile | Curly arrow from the C-Cl bond to the carbon atom |
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91 mark
What is the correct IUPAC name and classification of the following molecule?
| IUPAC name | Classification |
A | 1,bromopentane | Primary |
B | 2-bromopentane | Secondary |
C | 2-bromopentane | Primary |
D | 4-bromopentane | Secondary |
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101 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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11 mark
Four drops of 1-chloropentane, 1-bromopentane and 1-iodopentane 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 pentane chain C5H11– and X the halogen atom.
H2O (l) + R–X (l) + Ag+ (aq) → R–OH (aq) + AgX (s) + H+ (aq)
The rate of formation of cloudiness in the tubes was in the order RI > RBr > RCl
Why is this?
the R–X bond polarity decreases from RCl to RI
the electronegativity of the halogens decreases down the group
the bond enthalpy of R–X decreases from RCl to RI
the ionisation energy of the halogen 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
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?
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41 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 B C D | nucleophile electrophile nucleophile electrophile | nucleophile nucleophile electrophile electrophile |
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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
Aqueous sodium hydroxide reacts with 1-chlorobutane to give butan-1-ol.
How should the second step in the mechanism be described?
By a curly arrow from the C-Cl bond to the Cl atom
By a curly arrow from the Cδ+ to the C-Cl bond
By a curly arrow from the C–Cl bond to the C atom
By the homolytic fission of the C–Cl bond
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71 mark
What is the correct IUPAC name and classification of the following molecule?
| 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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81 mark
Which reagents and conditions are required for the following reaction to take place?
CH3CH2CH2I → CH3CH2CH2CN
heated under reflux, aqueous potassium cyanide
heated under reflux, ethanol, potassium cyanide
ethanol, potassium cyanide
warm, aqueous potassium cyanide
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91 mark
What would be a possible mix of products for the reaction when 2-iodopentane is warmed with ethanol and concentrated sodium hydroxide under reflux?
E-pent-2-ene, Z-pent-2-ene and pentan-1-ol
pent-1-ene, pent-2-ene
pent-1-ene, E-pent-2-ene and Z-pent-2-ene
pent-1-ene, pentan-2-ol
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101 mark
1-chloropropane is reacted with excess ammonia, NH3, in ethanol. Which of the following statements is correct?
The addition of excess ammonia favours the production of a tertiary amine, tripropylamine
A solid quaternary ammonium salt is formed due to further substitution
Excess ammonia favours the formation of a primary amine, propylamine
1-chloropropane is attacked by an NH3 molecule which can act as an electrophile
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11 mark
When a solution of potassium cyanide in ethanol is heated under reflux with 2-bromobutane, what is the organic product of the reaction called?
2-methylbutanenitrile
1-bromobutanenitrile
Butanenitrile
Pentanenitrile
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21 mark
Shown below is a reaction sequence starting with 1-chlorobutane and finishing with butene.
What is the correct reaction type and reagent for Step 1 and Step 2?
| Step 1 | Step 2 | ||
Type of reaction | Reagent(s) | Type of reaction | Reagent(s) | |
A | Nucleophilic substitution | H2O | Hydrolysis | Concentrated H3PO4 |
B | Addition | KCN in ethanol | Substitution | KCl (aq) and concentrated acid |
C | Nucleophilic substitution | NaOH (aq) | Elimination | Al2O3 |
D | Substitution | H2O | Substitution | KCN in ethanol |
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31 mark
A student mixes 2 cm3 of ethanol with 5 cm3 drops of different halogenoalkanes and warms the mixtures in a water bath at 50 °C. They then add silver nitrate solution. Which halogenoalkane will precipitate the fastest?
CH3C(CH3)ClCH3
CH3CHICH3
CH3C(CH3)ICH3
CH3CH2CH2I
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41 mark
How many different products can be formed if 3-bromo-2-methylpentane undergoes elimination?
2
3
4
5
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51 mark
The depletion of ozone, O3, is caused by the reaction of CFC molecules in the upper atmosphere. Ozone molecules are broken down into oxygen molecules.
What type of reaction is responsible for the depletion of ozone molecules?
Free radical addition
Propagation
Photolysis
Initiation
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61 mark
Which condition would see the production of a solid product from the nucleophilic substitution reaction between 1-iodopropane and ammonia?
A large excess of ammonia
Equal concentrations of ammonia and 1-iodopropane
Heating under reflux
A large excess of 1-iodopropane
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71 mark
Which are the correct product(s) for the reaction between 1-chlorobutane and ethanolic potassium hydroxide heated under reflux?
But-1-ene
A mixture of but-2-ene and butan-2-ol
Butan-2-ol
A mixture of but-1-ene and butan-1-ol
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81 mark
Which of the following mechanisms is not involved in the following reaction sequence?
Propane → 2-bromopropane → Propan-2-ol → Propene → 2-iodopropane
Electrophilic addition
Free radical substitution
Elimination
Nucleophilic addition
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91 mark
Which of the following is not a correct statement about hydrofluorocarbons, HFCs?
HFCs do not release free radicals in the stratosphere
HFCs are potent greenhouse gases
HFCs contain H-F bonds which have a lower bond enthalpy than H-Cl bonds
HFCs do not contribute to the destruction of the ozone layer
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101 mark
Which of the following descriptions of the elimination reaction mechanism is correct when 2-methyl-2-chlorobutane reacts with ethanolic sodium hydroxide?
| First step | Second step | Third step |
A | Curly arrow from lone pair on OH- to H atom in C-H bond adjacent to C-Cl | Curly arrow from C-H bond to C-C bond | Curly arrow from C-Cl bond to Cl atom |
B | Curly arrow from lone pair on OH- to δ+C atom | Curly arrow from C-C bond to C-H bond | Curly arrow from Cl atom bond to C-Cl atom |
C | Curly arrow from lone pair on OH- to H atom in C-H bond adjacent to C-Cl | Curly arrow from C-C bond to C-H bond | Curly arrow from Cl atom bond to C-Cl atom |
D | Curly arrow from lone pair on OH- to δ+C atom | Curly arrow from C-H bond to C-C bond | Curly arrow from C-Cl bond to Cl atom |
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