Q1 (a) Draw the structural formula of:
(i) an alkane with 4 carbon atoms (2)
(ii) an alkene with 4 carbon atoms (2)
(b) Draw the structural formula of the product(s) of reacting the alkane you have chosen with chlorine gas. (2)
(c) Draw the structural formula of the product(s) of reacting the alken you have chosen with chlorine gas. (2)
(d) The reaction of an alkene with bromine is used as a test for alkenes. Describe in detail how you would carry out this test and what you would see if the test proved to be positive.
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(3)
(e) Ethene, C2H4 can be converted to a
polymer called poly(ethene).
(i) Draw the structure of part of the poly(ethene) molecule clearly showing the
repeating unit. (2)
(ii) Classify the reaction for the formation of ploy(ethene)
from ethene as one of:
Free radical addition, electrophilic addition, hydrolysis or oxidation.
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(1)
(iii) Give one use of poly(ethene) (1)
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(15 Marks)
Q2. Alkanes are often used as fuels in a variety of
situations. Methane, CH4, is used as a gas to heat houses and
offices whereas octane, C8H18, is used in petrol.
Methane burns to form carbon dioxide and water as follows:
CH4 + 2O2 ---> CO2 + 2H2O
The enthalpy of combustion of methane is -890kJmol-1.
The enthalpy of combustion of octane is -5512kJmol-1.
Octance might seem a much better fuel than methane in all circumstances but this
is not necessarily so.
(a)(i) Define the term standard enthalpy of combustion.
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(3)
(ii) Why does methane not react with air unless a flame or
spark is applied to the mixture?
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(2)
(iii) Draw a reaction profile for the combustion of methane. (3)
(b)(i) Write a balanced equation for the complete combustion of octane in
oxygen.
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(2)
(ii) What volume of air, which contains 20% oxygen, would be needed to burn one mole of octane? (Under the conditions of the experiment, 1 mole of gas occupies 24dm3). (2)
(iii) Burning 1.00g of octane produces 48.4kJ of energy. Calculate the heat energy produced by burning 1.00g of methane.
(iv) Burning 1.00dm3 of liquid octane releases 33800kJ of energy. Calculate the heat energy released on burning 1.00dm3 of gaseous methane. Under the conditions of the experiment, 1 mole of gas occupies 24dm3). (2)
(v) Suggest why octane is preferred to methane as a fuel for
motor cars.
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(3)
(c) What role does methane play in the industrial production
of ammonia?
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(2)
(Total 21 marks)
Q3 The graph below shows the volume of hydrogen produced as
2.00g of magnesium ribbon reacts with 100cm3 of sulphuric acid,
concentration 1.00 mol dm-3.
(a) (i) Explain why the hydrogen is produced at a faster rate at
the beginning of the experiment than it is at the end of the experiment.
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(3)
(ii) With the aid of a
diagram of the Maxwell-Boltzmann distribution of molecular energies, explain why
raising the temperature by a small amount causes the rate of a chemical reaction
to increase by a large amount.
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(4)
(b) (i) Show by calculation whether magnesium or the sulphuric acid is in excess.(2)
(ii) Hence calculate the mass of hydrogen produced. (4)
(c) During the course of the experiment the temperature of the solution rises from 20oC to 42.5oC. Taking the specific heat capacity of the slutions as 4.2 Jg-1K-1, calculate the apparent enthalpy change for this reaction. (3)
Q4. Consider the following reaction scheme, involving
compounds A to E.
C3H8O (A) ----K2Cr2O7
in dilute sulphuric acid ---> C3H6O (B)
C3H8O (A) ---- conc sulphuric acid ---> (C)
--- HBr ---> (D)
None of the compounds in the scheme shows cis-trans isomerism.
D reacts with potassium cyanide to form 2-methylpropanonitrile.
An isomer of A will form C by the same route but will not produce B by reaction
with potassium dichromate (VI) acidified with dilute sulphuric acid.
Instead it makes E, C3H6O2.
Identify using a name or structural formulae:
A
B
C
D
E
(Total 10 Marks)
Q5. In this question you will need to use some or all of the
following terms
heterolytic, homolytic, electrophilic/electrophile, nucleophilic/nucleophile,
free radical, addition, substitution, oxidation, catalysis.
(a) Explain the meaning of the following terms.
(i) Electrophile.
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(2)
(ii) Nucleophile.
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(2)
(b) Explain the difference between heterolytic and homolytic
bond breaking.
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(2)
(c) Classify the following reactions using the terms listed at
the start of the question.
(i) The reaction between 2-chlorobutane and hydroxide ions.
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(2)
(ii) The reaction between ethanol and acidified potassium
dichromate solution.
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(1)
(d) A catalyst is used in the industrial manufacture of
sulphuric acid. Justify the economic benefits of using a catalyst in terms
of:
(i) the equilibrium involved:
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(2)
(ii) the kinetics of the reaction.
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(2)
Total Marks 13
Paper total 75 marks