Name: _______________________________________________
Mechanisms Revision Questions
Date:
Time: 40 minutes
Total marks available: 40
Total marks achieved: ______
RHS Chemistry Department
Q1. Alkenes are unsaturated hydrocarbons. They are used in the industrial production of many organic
compounds.
(a) Add structural formulae to the flowchart below to show the organic product formed in each addition
reaction of 2-methylpropene.
(4)
(b) Suggest a mechanism for the reaction of 2-methylpropene with bromine, Br2(l). Include curly arrows.
(3)
(c) Ethene, C2H4, was prepared from ethanol, C2H5OH, by the following reaction
C2H5OH → C2H4 + H2O
A chemist reacted 9.2 g of ethanol, C2H5OH, and obtained 4.2 g of ethene. Calculate the percentage
yield of ethene in the reaction.
(2)
(Total for Question = 9 marks)
Q2. An example of an alkene with six carbon atoms is 2-methylpent-1-ene. It reacts with chlorine by
means of an electrophilic addition reaction. The diagram below shows a student's attempt at drawing the
mechanism for this reaction.
(i) Identify the three errors in this student's drawing of the mechanism.
(3)
Error 1
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Error 2
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Error 3
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(ii) The structure of the carbocation intermediate is correctly drawn. Explain why the positive charge is on
the carbon atom shown.
(1)
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(Total for question = 4 marks)
Q3. Electrophiles are
A
electron pair donors that are attracted to regions of high electron density.
B
electron pair donors that are attracted to regions of low electron density.
C
electron pair acceptors that are attracted to regions of high electron density.
D
electron pair acceptors that are attracted to regions of low electron density.
(Total for question = 1 mark)
Q4.
(a) Which of the following represents a step in the mechanism during the reaction between ethene and
hydrogen bromide?
(1)
A
C2H4 + Br+ → C2H4Br+
C
C2H4 + HBr → C2H5• + Br•
B
C2H4 + HBr → C2H5+ + Br−
D
C2H4 + HBr → C2H4Br− + H+
(b) The mechanism of the reaction between ethene and hydrogen bromide is
(1)
A
electrophilic addition.
C
nucleophilic addition.
B
electrophilic substitution.
D
nucleophilic substitution.
(Total for question = 2 marks)
Q5.
The molecule shown above is 3-chloro-3-methylhexane. It reacts with hot, alcoholic potassium hydroxide
to produce a number of different alkenes. This reaction can be classified as
A
elimination.
C
reduction.
B
oxidation.
D
substitution.
(Total for question = 1 mark)
Q6. This question is about the reaction of methane with bromine in sunlight.
(1)
CH4 + Br2 → CH3Br + HBr
(a) This reaction is best described as
A
electrophilic addition.
C
free radical addition.
B
electrophilic substitution.
D
free radical substitution.
(b) One of the steps in the mechanism of this reaction is
(1)
•CH3 + Br• → CH3Br
This step is
A
initiation.
C
termination.
B
propagation.
D
reduction.
(c) This reaction produces a mixture of products. Which of the following is most likely to form, as well as
bromomethane?
(1)
A
ethane
C
butane
B
propane
D
pentane
(d) When human skin is overexposed to sunlight, it is likely to lead to skin cancer. What is the radiation
in sunlight that leads to skin cancer?
(1)
A
microwaves
C
visible light
B
infrared
D
ultraviolet
(Total for Question = 4 marks)
Q7. When trichloromethane, CHCl3, reacts with chlorine, the organic product is tetrachloromethane,
CCl4. The reaction proceeds by free radical substitution.
The equation for this reaction is
CHCl3 + Cl2 → CCl4 + HCl
(a) State the essential condition for this reaction to occur at room temperature.
(1)
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(b) The reaction mechanism involves free radicals. Explain what is meant by the term free radical.
(1)
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(c) The reaction takes place in a series of steps.
(i) The initiation step is
Cl2 → 2Cl•
Suggest why this initiation step is more likely than
CHCl3 → CCl3• + H•
(1)
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(ii) Write equations for the two propagation steps.
(2)
First propagation step
Second propagation step
(iii) Write an equation for the termination step in which tetrachloromethane is formed.
(1)
(d) Tetrachloromethane can be manufactured using the by-products of chlorination reactions.
C2Cl6 + Cl2 → 2CCl4
Compare the atom economy of this process with that of the reaction which produces
tetrachloromethane from trichloromethane and chlorine. A calculation is not required.
(1)
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(Total for question = 7 marks)
Q8. (a) The products of the reaction when 2-chlorobutane is heated with sodium hydroxide depend on
the conditions.
(i) What condition, other than a suitable temperature and sodium hydroxide concentration, would
produce a mixture of but-1-ene and but-2-ene?
(1)
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(ii) What type of reaction occurs in (a)(i)?
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(1)
(iii) What condition, other than a suitable temperature and sodium hydroxide concentration, would
produce butan-2-ol in the reaction of 2-chlorobutane with sodium hydroxide?
(1)
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(iv) Suggest the mechanism for the reaction of 2-chlorobutane with hydroxide ions to form butan-2-ol.
Use curly arrows to show the movement of electron pairs.
(2)
(b) Phosphorus(V) chloride, PCl5, can be used to test for the –OH group.
Describe what would be seen when phosphorus(V) chloride is added to butan-2-ol. Give the equation for
the reaction. State symbols are not required.
(2)
Observation
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Equation
(c) A tertiary alcohol, A, is an isomer of butan-2-ol.
(i) Butan-2-ol and A can be distinguished by warming separate samples with a mixture of potassium
dichromate(VI) and sulfuric acid. State the observations which would be made with each alcohol.
(2)
Observation with butan-2-ol
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Observation with A
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(ii) Give the structural formula of the organic product which forms when butan-2-ol is oxidized.
(1)
(iii) Explain how infrared spectroscopy could be used to detect whether butan-2-ol has been oxidized.
(1)
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(Total for Question = 11 marks)
Q9.
Samples of 1-chloropropane and 1-bromopropane are warmed with water containing dissolved silver
nitrate in the presence of ethanol. The 1-chloropropane reacts more slowly because
A
the C—Cl bond is more polar than the C—Br bond.
B
the C—Cl bond is stronger than the C—Br bond.
C
1-chloropropane is less soluble than 1-bromopropane.
D
1-chloropropane is a weaker oxidizing agent than 1-bromopropane.
(Total for Question = 1 mark)