Unit 1 – Alkanes
Unit 1 - Jan 2009
Q1.
 (a)  State the general formula of the alkanes, using the letter n to denote the number of carbon atoms in each molecule.
(1)

(b)  Alkanes are used as fuels. In the petrochemical industry, useful hydrocarbons are
       often produced from longer chain molecules.

       Name the type of reaction shown below.
(i)   
(1)
Type of reaction ....................................

(ii)   
(1)
Type of reaction ....................................

(c)  By what type of formula are the organic molecules in (b) represented?
(1)
........................................................................................................................................................................

(d)  Another reaction carried out in industry can be represented as shown below.

(i)   Give the molecular formula of compound 2.
(1)
........................................................................................................................................................................

(ii)   Give the name of compound 2.
(1)
........................................................................................................................................................................

(e)  An equation for the reaction between methane and chlorine is:

The reaction occurs in the presence of ultraviolet (UV) light via a free-radical chain mechanism.

 The initiation step is Cl2 → 2Cl

 The next step could be

(i)   Use the following data to calculate a value for the enthalpy change for each of the Steps, A and B.
(3)

Answer ....................................... kJ mol−1

Answer ....................................... kJ mol−1

(ii)   Use your answer to (i) to justify which of the Steps, A or B, is the more likely.
(1)
........................................................................................................................................................................
........................................................................................................................................................................
(f)  Another halogenoalkane, bromomethane, CH3Br, is a toxic gas used to protect plants against insects.

       Health and Safety advice states that concentrations above 5 parts per million (ppm) by volume of this gas are harmful.

       A research laboratory contains 2.5 × 105 dm3 of air.  Calculate the maximum volume of bromomethane, in dm3, allowed in the laboratory to comply with the advice given.
(1)

(Total for question = 11 marks)
Q2.
 How many isomers are there of C5H12?
   A     Two
   B     Three
   C     Four
   D     Five
(Total for question = 1 mark)

Unit 1 - Jun 2009
Q3.
Which of the following statements correctly describes an environmental problem caused
 by the burning of hydrocarbon fuels?
   A     The carbon dioxide is toxic and kills plants.
   B     The smoke produced reflects sunlight and leads to global warming.
   C     The water produced results in a damaging increase in rainfall.
   D     The carbon dioxide produced absorbs heat radiated from the Earth and leads to
                global warming.
(Total for question = 1 mark)

Q4.
This question is about hydrocarbons.
(a)  Liquefied petroleum gas (LPG) is a fuel sold as an alternative to petrol.  It is a
       mixture of liquefied C3 and C4 alkanes.
(i)  Suggest a reason why the alkanes are liquefied.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(ii)  There are two C4 alkanes. Draw skeletal formulae of each of the C4 alkanes in the spaces provided.
       Name each alkane.
(4)

(iii)  Complete the following sentence.
(1)
Compounds with the same molecular formula but different structural formula are called 

.........................................

(b)  Propane, C3H8, reacts with chlorine, Cl2, in a substitution reaction.

The mechanism for this reaction is described in three stages.
(i)  Give the initiation step for this reaction and state the condition necessary for this step to occur.
(2)
Initiation step

Condition
 ............................................................................................................................................. 
(ii)  Give the TWO propagation steps for this reaction.
(2)

(iii)  Give a possible termination step for this reaction.
(1)

(c)  Myrcene, C10H16, is a naturally occurring compound which is used in perfumes.

(i)  Name the functional group in myrcene.
(1)
 ............................................................................................................................................. 
(ii)  What colour change would you observe when bromine, dissolved in an organic solvent, is added to myrcene?
(1)
From .............................................................................. To 

(iii)  Classify the type and mechanism of the reaction that occurs when myrcene
        reacts with bromine, Br2.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(iv)  In an experiment, 1.36 g of myrcene (molar mass: 136 g mol−1) was found to react with 0.72 dm3 of hydrogen, H2, in the presence of a nickel catalyst.

        Use this information to draw the structural formula of the product of the reaction between myrcene and hydrogen.

        [Assume the molar volume of H2 under the conditions of the experiment is 24 dm3mol−1.]
(2)
Calculation

Hence structural formula of the product

(d)  Myrcene is one of a group of compounds related to 2-methylbut-2-ene shown below.

2-methylbut-2-ene undergoes addition polymerization in a similar way to ethene.

 Draw the structural formula of the repeat unit of the polymer formed.
(2)

(Total for question = 19 marks)
Q5.

Which of the following substances, obtained from the fractional distillation of crude oil, has the lowest boiling temperature?
   A     refinery gas
   B     kerosene
   C     diesel oil
   D     lubricating oil
(Total for question = 1 mark)

Unit 1 - Jan 2010
Q6.
Chloroethane, C2H5Cl, can be made from either ethane or ethene.
(a) (i) What reagent and condition would be used to make chloroethane from ethane?
(2)
Reagent
 ............................................................................................................................................. 
Condition
 ............................................................................................................................................. 
(ii) State the type of reaction and mechanism by which this reaction occurs.
(2)
 ............................................................................................................................................. 
(b) (i) What reagent would be used to make chloroethane from ethene?
(1)
 ............................................................................................................................................. 
(ii) Show, in full, the mechanism for this reaction in which ethene is converted to chloroethane.
(3)

(c) Which method of making chloroethane has
(3)
•   a higher atom economy?
 ............................................................................................................................................. 
•   a higher percentage yield?
 ............................................................................................................................................. 

 Explain your answers.
Higher atom economy
 ............................................................................................................................................. 
Higher percentage yield
 ............................................................................................................................................. 
 (d) The compound chloroethene, CH2=CHCl, forms an addition polymer.
(i) Draw a diagram, using dots or crosses, to show the arrangement of electrons in chloroethene. Only the outer shell electrons need be shown.
(2)

(ii) Chloroethene can form an addition polymer. Write the displayed formula of poly(chloroethene) showing two repeat units.
(1)

*(iii) Poly(chloroethene) is commonly known as PVC. Almost a quarter of the PVC which is manufactured is used to make water pipes, which were formerly made of metal.

                     Give TWO factors which have to be considered when deciding which material, PVC or metal, contributes to more sustainable uses of resources in the long term.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 16 marks)

Q7.
Which of the following mixtures could not form when octane, C8H18, is cracked?
   A      propane + pentene
   B      butane + butene
   C      pentane + propene
   D      heptane + ethene
(Total for question = 1 mark)
Unit 1 - Jun 2010
Q8.
This question is about ethene and related compounds.
(a) One way to manufacture ethene is by cracking hydrocarbon molecules such as liquid paraffin.
(i)  Name a raw material from which liquid paraffin can be obtained.
(1)
 ............................................................................................................................................. 
(ii)  Describe what is meant by cracking.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iii)  It was proposed to set up the apparatus below on a laboratory bench, in order to crack paraffin.

State TWO of the risks of using the apparatus in this way and suggest how you would amend the set-up to minimise each risk..
(4)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (b) Study the reaction scheme below and then answer the questions that follow.

(i)  Name the reagent and catalyst needed for Reaction 1.
(2)
Reagent
 ............................................................................................................................................. 
Catalyst
 ............................................................................................................................................. 
(ii)  Give the name and displayed formula of compound X.
(2)
Name
 ............................................................................................................................................. 
Displayed formula

(iii)  Describe what colour change you would see during Reaction 4 if a small  amount of acidified KMnO4(aq) was shaken with ethene.
(1)
From............................................................................................to................................................................

(c)  (i)  Use displayed formulae to show the mechanism for Reaction 3.
(3)

(ii)  Explain why the alkene, propene, could form two products when it reacts with
       hydrogen bromide in a similar way.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (d) The formula of the alkene phenylethene, often called styrene, is shown below. It can be used to make the polymer poly(styrene).

Draw a section of the poly(styrene) polymer chain formed from two monomer units.
(2)
(e) The table below shows some data used in a life cycle analysis of polystyrene and paper drinking cups.
(i)  Some people argue that using a polystyrene cup has less environmental impact
       than using a paper cup.
Choose TWO pieces of data to support this argument, explaining your choices.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
(ii)  Suggest TWO further pieces of information, not given in the table, regarding
       the life cycle of the cups that would make any assessment of the environmental
       impact more reliable.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for question = 22 marks)

Q9.
This question is about the properties of ions and ionic compounds.
(a) Solid calcium carbonate, CaCO3, has a giant ionic structure.
(i) Draw a diagram (using dots or crosses) for a calcium ion. Show ALL the electrons and the charge on the ion.
(2)

(ii) Complete the electronic configuration for a calcium ion.
(1)
1s2
 ............................................................................................................................................. 
(iii) Would you expect a calcium ion to be bigger, smaller or the same size as a
       calcium atom? Give TWO reasons to explain your answer.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iv) Explain why ionic compounds have relatively high melting temperatures.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (b) Changes in the concentration of ions in a solution can be estimated by measuring the
       electrical conductivity of the solution.
(i) Explain why solutions of ions are able to conduct electricity.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(ii) Suggest why aqueous solutions of calcium chloride, CaCl2(aq), and barium
      chloride, BaCl2(aq), of the same molar concentration, have different electrical
      conductivities.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iii) 1 kg of a solution contains 0.100 mol of calcium ions, Ca2+.

      What is the concentration of the calcium ions by mass in parts per million (ppm)?

      [Assume the relative atomic mass of calcium is 40.]
(2)

.....................................ppm

*(c) Some buildings are made from limestone, which is mainly calcium carbonate. Gases in the atmosphere such as sulfur dioxide, SO2, and nitrogen dioxide, NO2, can be responsible for damaging these buildings.
        Describe how these gases come to be present in the atmosphere and explain how they can damage a limestone building.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (d) The lattice energy of calcium chloride, CaCl2, is -2258 kJ mol-1 based on an experimental Born-Haber cycle and -2223 kJ mol-1 based on theoretical calculations.

      Would you expect its bonding to match the ionic model? Justify your answer.
(1)
 ............................................................................................................................................. 
............................................................................................................................................. 
(Total for question = 15 marks)

Q10.
The equations below show some of the processes that occur when methane and chlorine react.
 A     Cl2(g) → 2Cl•(g)
 B     Cl•(g) + CH4(g) → CH3•(g) + HCl(g)
 C     CH3•(g) + CH3•(g) → C2H6(g)
 D     Cl2(g) + CH4(g) → CH3Cl(g) + HCl(g)

(a) Which equation shows a propagation step?
(1)
   A
   B
   C
   D

(b) Which equation shows an initiation step?
(1)
   A
   B
   C
   D

(c) Which equation shows a termination step?
(1)
   A
   B
   C
   D
(Total for question = 3 marks)

Unit 1 - Jan 2011
Q11.
Alkenes are unsaturated hydrocarbons which, because of their reactivity, are important industrial starting materials. Alkenes for industrial use are obtained by cracking alkanes.
(a) Write the equation for the cracking of decane (C10H22) to form 1 molecule of propene as the only alkene.
(1)

(b) The carbon–carbon double bond in alkenes consists of a σ and a π bond.
(i) Explain, using diagrams, the difference between the σ and the π bond in the carbon–carbon double bond of an alkene.
(4)
Diagrams

Explanation
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(ii) State the type and mechanism involved in the typical reaction of alkenes.
(1)
 ............................................................................................................................................. 
*(iii) By considering the strength and structure of the π bond, explain why alkenes are more reactive than alkanes.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c) When propene reacts with hydrogen bromide, there are two possible products.
(i) Draw a displayed formula of each of these products and label the major product.
(2)

(ii) Give the mechanism for the reaction of propene with hydrogen bromide which forms the major product.
(3)

(iii) Explain, by referring to the mechanism, why the major product is formed.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(d) The polymer poly(propene) is manufactured from propene.
(i) Write an equation for the polymerization, drawing the displayed formula of the repeat unit of poly(propene).
(3)

(ii) UV radiation causes poly(propene) to degrade. Suggest one advantage and one disadvantage of this.
(2)
Advantage
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Disadvantage
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 20 marks)

Q12.
This question concerns the following compounds

Which of these compounds will show geometric (E–Z or cis/trans) isomerism?
   A
   B
   C
   D
(Total for question = 1 mark)
Q13.
Ethane reacts with chlorine when the substances are exposed to UV radiation.
(a) The equation for this reaction is
(1)
   A      C2H6 + Cl2 → C2H5Cl + HCl 
   B      C2H6 + Cl2 → C2H4Cl2 + H2
   C      C2H6 + Cl2 → 2CH3Cl 
   D      C2H4 + Cl2 → C2H4Cl2

(b) The role of the UV radiation in the reaction is to
(1)
   A       break the Cl—Cl bond forming Cl• free radicals. 
   B       break the Cl—Cl bond forming Cl+ and Cl− ions. 
   C       break the C—C bond in ethane forming CH3• free radicals. 
   D       break a C—H bond in ethane forming C2H5• free radicals. 

(c) The overall reaction between ethane and chlorine is best described as
(1)
   A       addition. 
   B       homolytic fission. 
   C       heterolytic fission. 
   D       substitution. 
(Total for question = 3 marks)
Unit 1 - Jun 2011
Q14.
This question is about alkanes.
(a) The skeletal formulae of two alkanes (A and B) are shown below.

      (i)   Write the general formula of the alkanes.
(1)

      (ii)  Compounds A and B are ................................................... of each other.
(1)
      (iii)  Draw the displayed formula of compound A.
(1)

      (iv)  Give the systematic name of compound B.
(1)
 ............................................................................................................................................. 

(b) The largest use for alkanes is as fuels. However, there are problems associated with the combustion of alkanes, whether complete or incomplete.
      (i)   An incomplete combustion of methane, CH4, results in the formation of carbon monoxide and water only.
Write the equation for this reaction. State symbols are not required.
(2)

      (ii)  When does incomplete combustion occur?
(1)
 ............................................................................................................................................. 
      (iii)  State two problems that result from the incomplete combustion of alkane fuels.
(2)
1 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
2 
 ............................................................................................................................................. 
 ............................................................................................................................................. 

    ∗(iv)  State and explain the main environmental problem arising from the complete combustion of alkane fuels.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c) The reactions of organic compounds, including alkanes, may be broken down into a series of steps; this is the mechanism for the reaction. The reaction between methane and chlorine may be represented by a mechanism involving three stages - initiation, propagation and termination.
      (i)   Reaction mechanisms often involve the use of 'curly arrows'. Explain the meaning of the curly arrows shown below.
(2)

Arrow I
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Arrow II
 ............................................................................................................................................. 
 ............................................................................................................................................. 
      (ii)  Using the curly arrow notation, show the initiation step of the reaction between methane and chlorine.
(2)

      (iii)  Give the two propagation steps of the reaction between methane and chlorine.
              Curly arrows are not required.
(2)

      (iv)  Suggest why a small amount of UV light can result in the formation of a large amount of product.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
      (v)   Ethane is a trace product of this reaction. By means of an equation, show how the ethane is formed.
(1)

(d) Scientists never detect molecular hydrogen, H2, amongst the products of the  chlorination of methane.
Use the data below to suggest why this is so.
The frequency of UV light used corresponds to an energy of about 400 kJ mol−1.

(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for Question = 22 marks)

Unit 1 - Jan 2012
Q15.
Chloroethane can be made from ethane and chlorine in the gas phase in the presence of ultraviolet light. The equation for the reaction is
CH3CH3 + Cl2 → CH3CH2Cl + HCl
(a) Complete the mechanism for the reaction. Two of the steps have been given for you.
(4)

(b) This reaction gives a poor yield of chloroethane. Give the structural formula and name of another organic product, not included in your mechanism for part (a), which could be produced in the reaction.
(2)
Formula
      ..............................................................................................................................................

(c) Chlorine gas is extremely toxic and is therefore a significant hazard. The preparation must be performed so as to minimise the risk to the experimenter.
     (ii)   Explain the difference between hazard and risk.
(2)
      ..............................................................................................................................................

      ..............................................................................................................................................

    (ii)   Give one precaution that you would use in this experiment to minimise the risk, other than the use of a laboratory coat and safety goggles.
(1)
      ..............................................................................................................................................
      ..............................................................................................................................................
(Total for question = 9 marks)

Q16.
How many compounds have the formula C5H12?
   A       1
   B       2
   C       3
   D       4
(Total for question = 1 mark)

Q17.
Which of the following is the correct order for the processes used to obtain petrol from
 petroleum (crude oil)?
   A       Petroleum → fractional distillation → reforming → petrol.
   B       Petroleum → reforming → fractional distillation → petrol.
   C       Petroleum → reforming → fractional distillation → petrol.
   D       Petroleum → fractional distillation → reforming → petrol.
(Total for question = 1 mark)
Q18.
An organic compound reacts with chlorine in the presence of ultraviolet light. The
 relative molecular mass of the product has increased by 34.5 compared with the original
 compound. What is the reaction mechanism?
   A       Free radical substitution
   B       Electrophilic substitution
   C       Nucleophilic substitution
   D       Free radical addition
(Total for question = 1 mark)

Unit 1 - Jun 2012
Q19.
When methane reacts with chlorine, a mixture of products forms. Which product provides the strongest evidence for a free radical mechanism?
   A    C2H6
   B    CH3Cl
   C    HCl
   D    CHCl3
(Total for question = 1 mark)

Q20.
What is the IUPAC name of the compound shown below?

   A    2-ethyl-2-propylpentane
   B    3-methyl-3-propylhexane
   C    4-methyl-4-propylhexane
   D    4-ethyl-4-methylheptane
(Total for question = 1 mark)

Unit 1 - Jan 2013
Q21.
This question is about the gas ethane, C2H6, and its reactions.
(a)  Write the equation, including state symbols, which represents the reaction taking place when the standard enthalpy change of combustion of ethane is measured.
(2)

(b)  Ethane can react with chlorine to form chloroethane and hydrogen chloride.

Rewrite this equation using displayed formulae.

 Use the equation you have written, together with the bond enthalpy data, to calculate the enthalpy change for the reaction.
(4)

(c)  This reaction takes place in a number of steps, some of which are shown below.

(i)   State the type of reaction occurring in step 1 and the conditions needed for this step.
(2)
Type
 ............................................................................................................................................. 
Conditions
 ............................................................................................................................................. 
(ii)   Complete the equation below for the third step of the reaction, and show the movement of electrons using the appropriate arrows.
(3)

(iii)   Write equations for two termination steps in this reaction.
(2)

(d)  Ethane can be cracked in industry.  Write an equation for the cracking of ethane.
(1)

(e)  Suggest two reasons why cracking of larger alkane molecules is important in industry.
(2)
Reason 1:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Reason 2:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 16 marks)

Q22.
Isomers have different
   A     empirical formulae.
   B     molecular formulae.
   C     skeletal formulae.
   D     molar masses.
(Total for question = 1 mark)

Unit 1 - Jun 2013
Q23.
Crude oil is a complex mixture of hydrocarbons. Initial separation is achieved by fractional distillation of the crude oil. The separate fractions are further refined to produce hydrocarbons such as decane, C10H22.

(a)  Give the general formula of alkanes.
(1)

(b)  Carbon monoxide, CO, is formed during the incomplete combustion of decane.

(i)  Write an equation for the incomplete combustion of decane, forming carbon monoxide and water only.
(1)

(ii)  Explain why incomplete combustion can occur.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(c)  'Low-sulfur fuel' is now supplied to petrol stations. The removal of sulfur from diesel and petrol reduces the emission of toxic oxides of sulfur from vehicle exhausts. One such oxide is sulfur dioxide, SO2.
The bonding in sulfur dioxide may be represented as shown below.
O = S → O
Complete the dot and cross diagram below for the SO2 molecule, showing only outer shell electrons. Use dots to represent the oxygen electrons and crosses to represent the sulfur electrons.
(3)

(d)  Another alkane produced from crude oil is heptane, C7H16. The reforming of heptane produces methylcyclohexane and only one other product. A methylcyclohexane molecule is made from a ring of six carbon atoms bonded to a methyl group.

(i)  Use the information given above to give the skeletal formula of methylcyclohexane.
(1)

(ii)  Write a balanced equation, using molecular formulae, for the reforming of heptane into methylcyclohexane and one other product. State symbols are not required.
(1)

(iii)  Suggest a reason why oil companies reform alkanes such as heptane.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(e)  Five branched-chain isomers of heptane are shown in the boxes below.

(i)  Give the systematic name of isomer A.
(1)
 ............................................................................................................................................. 

(ii)  In the empty boxes above, draw skeletal formulae for two other branched-chain isomers of C7H16, with no side-chain having more than one carbon atom.
(2)

(f)  Butane, C4H10, reacts with chlorine, Cl2, at room temperature and pressure.

C4H10 + Cl2 → C4H9Cl + HCl

(i)  What other condition is essential for this reaction?
(1)
 ............................................................................................................................................. 

(ii)  Write an equation for the initiation step of the mechanism for the above reaction. Curly arrows are not required.
(1)

(iii)  State the type of bond fission involved in the initiation step.
(1)
 ............................................................................................................................................. 

(iv)  Write equations for the two propagation steps of this mechanism. Curly arrows are not required.
(2)
First propagation step:

Second propagation step:

(v)  Write one equation for a reaction that would terminate this mechanism.
(1)

(Total for Question = 18 marks)

Q24.
Cracking crude oil
   A    separates the mixture into pure compounds.
   B    separates the mixture into a number of fractions.
   C    separates saturated compounds from unsaturated ones.
   D    decreases the average number of carbon atoms per molecule.

(Total for Question = 1 mark)

Q25.
This question is about ethene and its reactions.
Ethene is produced in industry by cracking.
(a)  (i)  Write the equation for the cracking of dodecane, C12H26, to produce one mole of ethene as the only alkene product.
(1)

(ii)  Draw a labelled diagram of the apparatus and materials you would use to crack dodecane and collect a sample of the gaseous alkene in the laboratory.
(4)

(b)  Draw a diagram to show the regions of electron density in both parts of the double bond between the carbon atoms in ethene. Label each region with appropriate symbols.
(2)

(c)  (i)  Give the name and structural formula for the product of the reaction between ethene and bromine, Br2(l).
(2)
Name
 ............................................................................................................................................. 

Formula

(ii)  Give the mechanism for the reaction between ethene and bromine.
(3)

(d)  Give the displayed formula for the organic product of the reaction between ethene and acidified potassium manganate(VII).
(1)

(e)  (i)  Write a balanced equation for the formation of poly(ethene) from ethene, showing the structure of the polymer clearly.
(2)

(ii)  Comment on the atom economy of the reaction in (e)(i).
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for Question = 16 marks)

Q26.
Which of the following is a major effect caused by increased carbon dioxide levels arising from the burning of fossil fuels?
   A    Melting of polar ice caps.
   B    Damage to the ozone layer.
   C    Increased acid rain.
   D    Increased skin cancer.
(Total for Question = 1 mark)

Q27.
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.
   B    electrophilic substitution.
   C    free radical addition.
   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.
   B    propagation.
   C    termination.
   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
   B    propane
   C    butane
   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
   B    infrared
   C    visible light
   D    ultraviolet
(Total for Question = 4 marks)
Unit 1 - Jun 2014
Q28.
Scientists are developing sources of energy as alternatives to fuels produced from crude oil. Which of the following reasons for doing this is incorrect?
(1)
   A    Crude oil is being used up faster than it is being formed.
   B    Burning hydrocarbons affects global carbon dioxide levels.
   C    Hydrocarbons from crude oil are a source of essential chemicals other than fuels.
   D    Carbon dioxide produced by burning hydrocarbons is toxic to plants.
otal for question = 1 mark)

Q29.
Crude oil is composed mainly of alkanes, which are saturated hydrocarbons.
(a)  (i)  Define the term hydrocarbon.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(ii)  State what is meant by the term saturated, as applied to a hydrocarbon.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(b)  Crude oil can be separated into fractions.
(i)  What property allows crude oil to be separated by fractional distillation?
(1)
 ............................................................................................................................................. 
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(ii)  Many chemists are of the opinion that we should use fuels such as biodiesel rather than petrol and diesel.
Suggest one reason to support this opinion.
(1)
 ............................................................................................................................................. 
............................................................................................................................................. 

(c)  A molecule of a hydrocarbon, X, can be cracked to form one molecule of pentane, C5H12, and two molecules of ethene only.
(i)  Deduce the molecular formula of X.
(1)

(ii)  Give one reason why cracking reactions are carried out in industry and suggest why high temperatures are used in this process other than to speed up the reaction.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
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(d)  Butane, C4H10, is a hydrocarbon which is used as a fuel. It is a gas under standard conditions.
(i)  Explain what is meant by the term fuel.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(ii)  Write an equation for the complete combustion of butane under standard conditions. Include state symbols in your answer.
(2)

(iii)  Write an equation for the incomplete combustion of butane to form carbon monoxide and water only. State symbols are not required.
(1)

(iv)  Under what conditions would you expect incomplete combustion to occur?
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(e)  Butane can react with bromine, in the presence of ultraviolet radiation, according to the following equation.
C4H10 + Br2 → C4H9Br + HBr
(i)  Calculate the atom economy by mass for the formation of C4H9Br. 
Use the expression

Use the Periodic Table as a source of data.
(2)

Final answer = ........................................................... %

*(ii)  Describe the mechanism of the reaction between butane and bromine that forms the products given in the equation below.
C4H10 + Br2 → C4H9Br + HBr
In your answer you should include
·	equations for each step of the mechanism (curly arrows are not required)
·	the name of each step occurring in the mechanism. 
(7)

  
(Total for question = 21 marks)

Q30.
Which of the following molecules does not contain a double bond?
   A    CO2
   B    C2Cl4
   C    C3F8
   D    C2H2Cl2
(Total for question = 1 mark)

Q31.
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)
 ............................................................................................................................................. 

(b)  The reaction mechanism involves free radicals. Explain what is meant by the term free radical.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(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)
 ............................................................................................................................................. 

(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)
 ............................................................................................................................................. 
(Total for question = 7 marks)

Q32.
What is the systematic name for the hydrocarbon shown below?

   A    1,4-dimethylbutane
   B    2,3-dimethylbutane
   C    2,3-dimethylhexane
   D    1,1,2,2-tetramethylethane
(Total for question = 1 mark)

Q33.
This question is about the organic compounds shown below.

(a)  The compounds which are isomers are
(1)
   A    W and X
   B    W and Y
   C    W and Z
   D    X and Z

(b)  Which compound can react with chlorine to form C6H12Cl2 as the only product?
(1)
   A    Compound W
   B    Compound X
   C    Compound Y
   D    Compound Z

(c)  Which compound is reformed in the oil industry, producing one mole of a compound with formula C6H6 and four moles of hydrogen, H2, only?
(1)
   A    Compound W
   B    Compound X
   C    Compound Y
   D    Compound Z
(Total for question = 3 marks)

Q34.
Propane is a saturated hydrocarbon with molecular formula C3H8.
*(a)  Explain the meaning of the terms saturated and hydrocarbon.
(2)
Saturated
 ............................................................................................................................................. 
 ............................................................................................................................................. 

Hydrocarbon
 ............................................................................................................................................. 
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(b)  Propane is sold in small cylinders for use as a fuel in camping stoves. The enthalpy change of combustion of propane can be measured by experiment using one of these cylinders.
A known mass of propane is burned to heat a container of water, and the temperature rise of the water is measured.
The results of the experiment are shown below.

(i)  How would the mass of propane which was burned be measured?
(1)
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 ............................................................................................................................................. 

(ii)  Calculate the energy transferred in the experiment, using the results above and the following expression.
Energy transferred (J) = mass × specific heat capacity × temperature change
The specific heat capacity of water is 4.18 J g−1 °C−1.
(1)

(iii)  Calculate the enthalpy change of combustion of propane, ΔHc, in kJ mol−1.
Give your answer to three significant figures and include a sign.
(3)

(iv)  The results of this experiment are inaccurate due to heat loss.
Suggest one other source of error, other than measurement errors and limitations of the equipment.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(c)  Another way of calculating the enthalpy change of combustion for propane is to use mean bond enthalpy data.

(i)  Complete the equations in the Hess cycle below. The enthalpy change of +6490 kJ mol−1 is the total energy required to break the bonds in propane and in oxygen.
(1)

(ii)  Use the data in the table to calculate the enthalpy change, Z, in kJ mol−1.

(1)

(iii)  Use the cycle in (c)(i), and your answer to (c)(ii), to calculate the enthalpy change, ΔHx, in kJ mol−1, for the combustion of propane.
(1)

(iv)  The data book value for the standard enthalpy change of combustion, , for propane is −2219.2 kJ mol−1. This value is more exothermic than that calculated using mean bond enthalpy data. Give one reason for this.
(1)
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 ............................................................................................................................................. 
  
(Total for question = 12 marks)