AS & A Level Chemistry 15.1 Halogenoalkanes: Exam Style Questions Paper 1

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Question:

In which reactions is the major product formed by a nucleophilic substitution reaction?

1 bromoethane + potassium cyanide in ethanol
2 bromoethane + ammonia in ethanol under pressure
3 bromoethane + hot concentrated sodium hydroxide in ethano

▶️Answer/Explanation

Ans:B

Question:

The diagram shows the structure of a bromo compound that may be formed by the reaction of bromine with a hydrocarbon.

Which row is correct?

▶️Answer/Explanation

Ans:D

Question

lodoethane, $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{I}$, reacts with aqueous silver nitrate at $50^{\circ} \mathrm{C}$. A precipitate forms during this reaction.
Which row of the table is correct about this reaction?

▶️Answer/Explanation

Ans:D

Question

A student converts 1-iodopropane, $\mathrm{C}_3 \mathrm{H}_7 \mathrm{I}$, into butanoic acid, $\mathrm{C}_3 \mathrm{H}_7 \mathrm{CO}_2 \mathrm{H}$, by a two-stage chemical synthesis.
In the first of the two stages, which reagent is reacted with 1-iodopropane?
A aqueous sodium hydroxide
B ethanolic ammonia
C ethanolic potassium cyanide
D ethanolic sodium hydroxide

▶️Answer/Explanation

Ans:C

Question

1-chloro-1-methylcyclohexane is hydrolysed by heating with $\mathrm{NaOH}(\mathrm{aq})$.

The reaction pathway is shown.

One carbon atom in 1-chloro-1-methylcyclohexane is bonded to three other carbon atoms.
What is the charge on this carbon atom at point $Z$ ?
A $1-$
B $\delta-$
C $\delta^{+}$
D $1+$

▶️Answer/Explanation

Ans:D

Question

2-bromo-2-methylpentane is a tertiary halogenoalkane.
Which organic products are formed when 2-bromo-2-methylpentane reacts with a hot
concentrated ethanolic solution of sodium hydroxide?

A 2-methylpent-1-ene only
B 2-methylpent-1-ene and 2-methylpent-2-ene
C 2-methylpent-2-ene only
D 2-methylpent-2-ene and 4-methylpent-2-ene

▶️Answer/Explanation

Ans:B

Question

Chlorofluoroalkanes that diffuse into the stratosphere are broken down by ultraviolet radiation.
Radicals are generated that cause depletion of ozone.
What are these radicals?

1 chlorine radicals
2 fluorine radicals
3 alkyl radicals

▶️Answer/Explanation

Ans:D

Question:

Which statements apply to tetrafluoromethane?

1 It is rapidly decomposed by ultraviolet radiation.
2 It is less harmful to the ozone layer than dichlorodifluoromethane.
3 It is a non-polar molecule.

▶️Answer/Explanation

Ans:C

Question

Which statements help to explain the mechanism of the reaction between 1-chloropropane and ammonia?
1 1-chloropropane has a $\delta$ – chlorine atom that forms hydrogen bonds with a $\delta+$ hydrogen atom in ammonia.
2 1-chloropropane is a polar compound with a $\delta+$ carbon atom.
3 There is a lone pair of electrons on the nitrogen atom in ammonia.

▶️Answer/Explanation

Ans:C

Question

Propene undergoes a variety of reactions.
Which row is correct?

▶️Answer/Explanation

Ans:C

Question

Which radical is most likely to form by the homolytic fission of one covalent bond in bromochloromethane, $\mathrm{CH}_2 \mathrm{BrCl}$ ?
A $\cdot \mathrm{CH}_2 \mathrm{Cl}$
B $\cdot \mathrm{CH}_2 \mathrm{Br}$
C $\cdot \mathrm{CHBrCl}$
D $\cdot \mathrm{CH}_2 \mathrm{BrCl}$

▶️Answer/Explanation

Ans:A

Question

The diagram shows the structures of three halogenoalkanes.

P, Q and R can all be hydrolysed.
Which row is correct?

Answer/Explanation

Ans: A

Question

A reaction occurs when a sample of 1-chloropropane is heated under reflux with sodium hydroxide dissolved in ethanol.
Which row is correct?

Answer/Explanation

Ans: B

Question

Bromoethane reacts with cyanide ions, producing propanenitrile.

Which statement about the S_N2 mechanism of this reaction is correct?

A The lone pair of electrons on C of CN^– attacks the carbon atom of the C–Br bond.

B The lone pair of electrons on C of CN^– attacks the carbocation formed when the C–Br bond breaks.

C The lone pair of electrons on N of CN^– attacks the carbon atom of the C–Br bond.

D The lone pair of electrons on N of CN^– attacks the carbocation formed when the C–Br bond breaks.

Answer/Explanation

Answer: A

Question

The table describes four reactions of propene.

Which row is correct?

Answer/Explanation

Answer: C

Question

Which statements are correct?

1 1,1-difluoroethane is less reactive than 1,1-dichloroethane.
2 1,1-difluoroethane is polar.
3 The C–F bond is stronger than the C–Cl bond.

Answer/Explanation

Answer: A

Question

Which statements about chlorofluoroalkanes are correct?

1 Both the C–Cl and C–F bonds are readily dissociated by ultra-violet light.
2 They have caused ozone depletion.
3 They are relatively chemically inert.

▶️Answer/Explanation

Answer C

Question

When an organic compound, Q, is treated with phosphorus pentachloride, fumes of hydrogen chloride are evolved. When Q is warmed with acidified aqueous potassium dichromate(VI), the solution turns green.

What is Q?

A CH ₃CH ₂CHO
B CH₃CH₂CO₂H
C CH₃CH(OH)CH₃
D (CH₃)₃COH

Answer/Explanation

Answer C

Question

Bromopropane reacts with water as shown.

CH₃CH₂CH₂Br + H₂O → CH₃CH₂CH₂OH + HBr

Which statement is correct?
A This is an elimination reaction.
B This is a hydrolysis reaction.
C This is a redox reaction.
D This reaction tends to proceed via the SN1 mechanism.

Answer/Explanation

Answer:

Question

Bromoethane and chloroethane are added separately to water. Hydrolysis reactions occur.

Which compound hydrolyses more rapidly and what is the mechanism?

Answer/Explanation

Answer B

Question

A tertiary bromoalkane, indicated here by , reacts with aqueous NaOH. The mechanism has the reaction pathway shown.

Which point in the diagram is correctly identified?

Answer/Explanation

Answer C

Question

The structure of coniine is shown.

Coniine can be synthesised by reacting ammonia with a dibromo compound, X.

NH₃ + C₈H₁₆Br₂ → coniine + 2HBr

What is the name of compound X?

A 1,1-dibromo-2-propylcyclopentane
B 1,2-dibromo-2-propylcyclopentane
C 1,4-dibromooctane
D 1,5-dibromooctane

Answer/Explanation

Answer D

Question

Which reaction is most likely to involve the formation of a positively charged intermediate?

A 1-bromopentane and warm dilute NaOH(aq)
B 1-bromo-2,2-dimethylpropane and warm dilute NaOH(aq)
C 1-bromo-3-methylbutane and warm dilute NaOH(aq)
D 2-bromo-2-methylbutane and warm dilute NaOH(aq)

Answer/Explanation

Answer D

Question

The halogenoalkanes listed below all react with NaOH(aq).

Which reactions proceed mainly by an S_N1 mechanism?

1 1-iodopropane
2 2-iodo-2-methylpropane
3 2-bromo-2-methylbutane

Answer/Explanation

Answer C

Question

Chlorofluoroalkanes have been used as the refrigerant in refrigerators but care has to be taken in
disposing of old refrigerators.

Which statements about chlorofluoroalkanes are correct?

1 C–Cl bonds more readily undergo homolytic fission than C–F bonds.

2 Care is taken in the disposal of old refrigerators because of possible ozone depletion.

3 C₂H₄ClF is more volatile than C₂H₆.

Answer/Explanation

Answer B

Question

Organic compound X gives a precipitate when warmed with aqueous silver nitrate. This precipitate dissolves when concentrated aqueous ammonia is added.

What could X be?
1 1-bromopropane
2 2-chlorobutane
3 2-iodo-2-methylpropane

The responses A to D should be selected on the basis of

Answer/Explanation

Answer:

Question

The following statements are about the reaction of NaOH(aq) with the three chloroalkanes shown.
$CH_3CH_2CHClCH_3$ $(CH_3)_2CHCH_2Cl$ $(CH_3)_3CCl$

Which statements are correct?
1 $(CH_3)_2CHCH_2Cl$ reacts with NaOH(aq) by an $S_N2$ mechanism.
2 The tertiary chloroalkane reacts more quickly than the others because the carbon atom bonded to the Cl atom is more positive in this molecule.
3 The Cl atoms in the three chloroalkanes are attacked by $OH^–$

The responses A to D should be selected on the basis of

Answer/Explanation

Ans: D

Question

Which types of reaction can occur with 1-bromobutane?

1 elimination

2 hydrolysis

3 free radical substitution

Answer/Explanation

Answer: A

Question

If the starting material is iodoethane, which sequence of reactions will produce propanoic acid as the main final product in good yield?
A add NaOH(aq), isolate the organic product, add acidified $K_{2}Cr_{2}O_{7}$ and boil under reflux
B add NaOH(aq), isolate the organic product, add \$H_{2}SO_{4}$(aq) and boil under reflux
C heat with HCN in ethanol, isolate the organic product, add$ H_{2}SO_{4}$(aq) and boil under reflux
D heat with KCN in ethanol, isolate the organic product, add $H_{2}SO_{4}$(aq) and boil under reflux

Answer/Explanation

Ans:D

Question

X is an organic compound that gives a precipitate with aqueous silver nitrate. This precipitate remains undissolved when concentrated aqueous ammonia is added.
What is a possible identity for X?
1 iodomethane
2 2-bromobutane
3 2-chlorobutane

The responses A to D should be selected on the basis of

▶️Answer/Explanation

Ans:D

Question

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

Answer/Explanation

Ans:D

Question

The hydrolysis of 1- chloropropane to produce propan-1-ol is much slower than the corresponding hydrolysis of 1-iodopropane.
Which statement explains this observation?

A Chlorine is more electronegative than iodine.

B The bond strength of the C–I bond is less than that of the C–Cl bond.

C The carbon atom in the C–Cl bond is more δ+ than that in the C–I bond.

D The hydrolysis involves a nucleophilic addition reaction.

Answer/Explanation

Ans:B

Question

Which reaction will give the best yield of 1-chloropropane?
A    chlorine gas with propene gas in the dark
B    propan-1-ol with dilute NaCl(aq)
C    propan-1-ol with $PCl_5$
D    propene with dilute HCl(aq)

Answer/Explanation

Ans: C

Question

Aluminium chloride catalyses certain reactions by forming carbocations with chloroalkanes as shown.

RCl + Al Cl₃ → R⁺+ Al Cl ₄^–

Which property makes this reaction possible?

AlCl₃ exists as the dimer Al₂Cl₆ in the vapour.
AlCl₃ is a covalent molecule.
The aluminium atom in Al Cl₃ has an incomplete octet of electrons.
The chlorine atom in RCl has a vacant p orbital.

Answer/Explanation

Ans:

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