Unit 2 – Halogenoalkanes
Unit 2 - Jan 2009
Q1.
This question is about the reactions and properties of some halogenoalkanes.
(a)  State the reagents and conditions needed to convert the following halogenoalkanes into the named product.
(i)   1-bromobutane into butan-1-ol
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (ii)   1-iodobutane into butylamine
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iii)   2-chloropropane into propene
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (b)  Chloroethane can be prepared by reacting ethanol with potassium chloride in the presence of concentrated sulfuric acid.

        Explain why a similar reaction using potassium iodide and concentrated sulfuric acid should not be used to prepare iodoethane.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c)  Two gaseous halogenoalkanes that could be used as fire retardants have the structural formulae CF2ClBr and CF3CHF2.
(i)   Give the systematic name of CF2ClBr.
(1)
 ............................................................................................................................................. 
(ii)   Draw the skeletal formula of CF3CHF2.
(1)

(iii)   Suggest TWO reasons to explain how these compounds can help put out fires.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
*(iv)   Explain why fire retardants containing some halogenoalkanes, such as CF2ClBr, are being phased out.
         Suggest a reason why the scientific community still supports the use of fire retardants containing CF3CHF2.
(4)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
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 ............................................................................................................................................. 
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(Total for question = 16 marks)

Unit 2 - Jun 2009
Q2.
Which of these compounds is a secondary halogenoalkane?
   A     CH3CH(OH)CH3
   B     CH3CCl(CH3)CH3
   C     CH3CHClCH3
   D     CH3CH2CH2Cl
(Total for question = 1 mark)

Q3.
When 2-chloro-2-methylpropane is heated in a mixture of water and ethanol at 65 °C, two types of reaction occur.  A mixture of two organic products, 2-methylpropan-2-ol and 2-methylpropene, is formed.

(a)  (i)  Name the two reaction types that are taking place.
(2)
Reaction 1
 ............................................................................................................................................. 
Reaction 2
 ............................................................................................................................................. 
*(ii)  Explain how the two products form, by describing the role of the water in each
         case.
(4)
Reaction 1
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Reaction 2
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (b)  A proposed mechanism for Reaction 1 involved the formation of the carbocation,

(i)  What type of bond breaking must have occurred during the carbocation
       formation?
(1)
 ............................................................................................................................................. 
(ii)  Suggest why 1-chlorobutane reacts with water via a different mechanism.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(c)  Another halogenoalkane, 2-chlorobutane, behaves in a similar way to 2-chloro-2-methylpropane but in Reaction 2 can form three different alkenes. Suggest how three different alkenes can form and give their displayed formulae.
(4)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(d)  Suggest why 2-fluoro-2-methylpropane would react more slowly than 2-chloro-2-methylpropane in Reaction 1.
        What reagent could you use instead of water to increase the rate of this reaction involving 2-fluoro-2-methylpropane? Explain why the reagent would have this effect.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
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 (Total for question = 16 marks)
Unit 2 - Jan 2010
Q4.
Chloroethane reacts with aqueous potassium hydroxide solution, producing ethanol as the organic product.
(a)  The hydroxide ion is acting as
(1)
   A     an electrophile.
   B     a nucleophile.
   C     an oxidizing agent.
   D     a reducing agent.

(b)  Which of the following shows the correct electron-pair movements in this reaction?
(1)

(Total for question = 2 marks)

Q5.
Butan-1-ol and three other alcohols, X, Y and Z, are isomers.
(a)  (i)  Give TWO observations you would make when any one of the alcohols reacts with sodium.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (ii)  Give the molecular formula of the organic product of the reaction.
(1)
 ............................................................................................................................................. 
(b)  Isomer X does not react with a mixture of potassium dichromate(VI) and sulfuric acid.
Draw the displayed formula of X and name it.
(2)

Name
 ............................................................................................................................................. 
(c)  When isomer Y is heated under reflux with a mixture of potassium dichromate(VI) and sulfuric acid, it forms 2-methylpropanoic acid.
Deduce the structural formula of the alcohol Y.
(1)

(d)  (i)  Isomer Z reacts with a mixture of potassium dichromate(VI) and sulfuric acid to form a compound Q, which does not react with Fehling's or Benedict's solution.
Deduce the structural formula of the alcohol Z.
(1)

(ii)  What would be the principal difference between the infrared spectrum of Q and the infrared spectrum of 2-methylpropanoic acid?
You are not expected to quote absorption values.
(1)
 ............................................................................................................................................. 
 (e)  One of the isomers, X, Y or Z can be converted to 2-chlorobutane.
What reagent would you use to carry out this conversion?
(1)
 ............................................................................................................................................. 
(f)  (i)  2-chlorobutane reacts with silver nitrate in a mixture of ethanol and water as a solvent. What would you see when the reaction occurred?
(1)
 ............................................................................................................................................. 
*(ii)  Both ethanol and water contain hydrogen bonds. By considering the hydrogen bonding on these two solvents, suggest why 2-chlorobutane is more soluble in ethanol than in water.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for question = 12 marks)

Q6.
When chloroethane is heated with a concentrated solution of potassium hydroxide in ethanol, the reaction which occurs is
   A     substitution.
   B     elimination.
   C     hydrolysis.
   D     redox.
(Total for question = 1 mark)

Unit 2 - Jun 2010
Q7.
This question is about the chemistry of some halogenoalkanes.

Halothane is a colourless and sweet-smelling liquid. It has a boiling temperature of 50°C. Halothane vapour was used as a general anaesthetic in hospitals during the mid to late 20th Century. Patients inhaled the halothane vapour under medical supervision. However, halothane was found to have some adverse side-effects and was therefore replaced by other halogenoalkane anaesthetics.
Halothane has the structure

In an experiment, halothane was heated in a test tube with aqueous silver nitrate and ethanol, using a water bath. Compound X and bromide ions were formed. The structure of compound X is shown below.

(a)  (i)  Give the systematic name of halothane.
(1)
 ............................................................................................................................................. 
(ii)  Suggest the types of intermolecular force present between molecules of liquid halothane.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(iii)  In the above experiment, suggest ONE reason why a water bath was used rather than heating the test tube containing the reaction mixture directly over a Bunsen flame.
(1)
 ............................................................................................................................................. 
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 (iv)  Suggest why ethanol was used in this experiment.
(1)
 ............................................................................................................................................. 
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 (v)  What would be seen in the test tube as the reaction progressed?
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(vi)  Write an ionic equation to show the reaction between aqueous silver ions and aqueous bromide ions. Include state symbols in your equation.
(1)

(b)  Chloroethane, C2H5Cl, can also be used as an anaesthetic. In an experiment, chloroethane was hydrolysed by aqueous sodium hydroxide, NaOH.
(i)  Name, and give the structural formula of, the organic product of the hydrolysis of chloroethane.
(2)
Name
 ............................................................................................................................................. 
Structural formula
 ............................................................................................................................................. 
(ii)  The hydrolysis of chloroethane is an exothermic reaction which takes place in a single step.
On the diagram below, draw the energy profile for the reaction. Label clearly the activation energy for the reaction.
(3)

(c)  In the early 1900s, the CFC with formula CCl2F2, was identified as a refrigerant which was both non-flammable and non-toxic.
(i)  What does the term CFC stand for?
(1)
 ............................................................................................................................................. 
(ii)  Suggest ONE use for CFCs other than as a refrigerant.
(1)
 ............................................................................................................................................. 

*(iii)  In the stratosphere, CFCs are broken down by absorption of UV radiation to form chlorine free radicals.
The following two reactions occur.

Combine these two equations to give the overall equation for the reaction of ozone in the stratosphere. State the role played by the chlorine free radical in the overall reaction. Hence explain why many scientists consider the effect of CFCs on ozone to be harmful.
(5)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
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 (d)  The compound of formula CH2F2 has replaced several CFCs for commercial use. If molecules of CH2F2 reach the stratosphere, they do not break down to produce fluorine free radicals.
(i)  Suggest why C-F bonds are not broken in the stratosphere.
(1)
 ............................................................................................................................................. 
*(ii)  The compound CH2F2 acts as a greenhouse gas when it absorbs a particular type of radiation.
Name the type of radiation and explain why a molecule of CH2F2 is able to absorb this radiation.
(2)
 ............................................................................................................................................. 
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 (Total for question = 22 marks)

Unit 2 - Jan 2011
Q8.
This question is about iodine and its compounds.
(a) (i) The element iodine can be obtained from seaweed. One step in the procedure is to extract the iodine from aqueous solution by shaking with a hydrocarbon solvent in a separating funnel.

        Draw a diagram of a separating funnel containing the separated layers. Label the hydrocarbon layer, and state its colour.
        [Density of hydrocarbon layer 0.660 g cm−3]
(3)
Diagram

Colour of hydrocarbon layer
 ............................................................................................................................................. 
     (ii) Iodine is also formed when an aqueous solution containing iodide ions reacts with an aqueous solution of iron(III) ions.

          Write the ionic equation for this reaction. State symbols are not required.
(1)

(b) Hydrogen iodide gas is usually prepared by adding phosphoric(V) acid to solid potassium iodide.
(i) Suggest why phosphoric(V) acid is used in this preparation rather than concentrated sulfuric acid.
(1)
 ............................................................................................................................................. 
 (ii) Describe what you would see if a test tube of hydrogen iodide gas was inverted in a beaker of water.
(1)
 ............................................................................................................................................. 
 (iii) When hydrogen iodide gas reacts with ammonia, dense white fumes form.

                    Write the equation for this reaction, including state symbols.
(2)

(c) 1-iodobutane can be made by reacting butan-1-ol with phosphorus(III) iodide, PI3, formed by reacting moist red phosphorus with iodine.
(i) Complete the following equation for the formation of 1-iodobutane.
(1)
PI3 + .................... C4H9OH →

(ii) Identify the intermolecular forces present between molecules of 1-iodobutane.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iii) 1-iodobutane reacts with hot aqueous silver nitrate solution. Describe what you would see when this reaction takes place.
(1)
 ............................................................................................................................................. 
(iv) Give the structural formula for the organic product of the reaction between 1-iodobutane and ammonia.
(1)

(Total for question = 12 marks)

Unit 2 - Jun 2011
Q9.
This question is about the element chlorine and its compounds.
(a) When chlorine is bubbled through water, a solution of chlorine water forms. What is the colour of chlorine water?
(1)
 ............................................................................................................................................. 
(b) Chlorine water is added to potassium iodide solution.
      (i)   State the colour of the solution produced.
(1)
 ............................................................................................................................................. 
      (ii)  Write the ionic equation for the reaction, including state symbols.
(2)

(c) The concentration of chlorine water was found by taking 10.0 cm3 of solution, adding an excess of potassium iodide solution, and titrating with 0.0100 mol dm−3 of sodium thiosulfate solution. The experiment was repeated.
      The following results were obtained.

      (i)   Name a suitable indicator for the titration. State the colour change you would expect to see at the end point.
(2)
Indicator ...........................................

Colour change from ........................................... to ...........................................

   (ii)  Calculate the mean titre and use this value to calculate the number of moles of sodium thiosulfate used in the titration.
(1)
Mean titre = .................................... cm3

Moles of sodium thiosulfate

      (iii)  Complete the ionic equation for the reaction between iodine and thiosulfate ions.
(2)

      (iv)  Calculate the number of moles of iodine which reacted with the sodium thiosulfate solution.
(1)

      (v)   Hence state the number of moles of chlorine present in 10.0 cm3 of the chlorine water.
(1)

      (vi)  Calculate the concentration of the chlorine water, in mol dm−3.
(1)

(d) Potassium burns in chlorine to form potassium chloride.
      (i)   Give the colour of the flame when potassium burns in chlorine.
(1)
 ............................................................................................................................................. 
      (ii)  Write the equation for the reaction between potassium and chlorine. State symbols are not required.
(1)

(e) Concentrated sulfuric acid is added to potassium chloride in a test tube. Steamy fumes are given off which react with ammonia to give dense white smoke.
      (i)   Name the gas given off in this reaction.
(1)
 ............................................................................................................................................. 
      (ii)  Steamy fumes are observed at the mouth of the test tube. Explain how these fumes are formed.

(1)
 ............................................................................................................................................. 
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      (iii)  The steamy fumes react with ammonia to give a dense white smoke. Identify the white smoke by name or formula.
(1)
 ............................................................................................................................................. 
(f) 2-chlorobutane can be made from butan-2-ol.
     (i)   Name the chemical you would add to butan-2-ol in the laboratory to make 2-chlorobutane.
(1)
 ............................................................................................................................................. 
     (ii)  2-chlorobutane reacts with alcoholic potassium hydroxide at a high temperature to form a mixture of gaseous alkenes.
            Draw a fully labelled diagram of the apparatus you would use to prepare and collect this mixture.
(3)

(Total for Question = 21 marks)

Q10.
This question is about ethanethiol, CH3CH2SH. Thiols are like alcohols, but the oxygen atom has been replaced by a sulfur atom. They react in a similar way to alcohols.
(a) (i)   Draw a dot and cross diagram for ethanethiol, showing outer electrons only.
(2)

    (ii)  Give the value for the CSH bond angle in ethanethiol. Justify your answer.
(3)
CSH angle .........................
Justification
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (b) There are hydrogen bonds between ethanol molecules but not between ethanethiol molecules.
      (i)   Explain why the bond angle around the hydrogen atom involved in a hydrogen bond is 180°.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
      (ii)  Explain why there are no hydrogen bonds between ethanethiol molecules.
(1)
 ............................................................................................................................................. 
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(c) (i)   Describe the formation of London forces.
(2)
 ............................................................................................................................................. 
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      (ii)  Explain why the London forces in ethanethiol are stronger than those in ethanol.
(1)
 ............................................................................................................................................. 
(d) The reaction of sodium with ethanethiol, CH3CH2SH, is similar to its reaction with ethanol.
      (i)    Suggest one observation you would make when sodium is added to ethanethiol.
(1)
 ............................................................................................................................................. 
      (ii)   Suggest a balanced equation for this reaction. State symbols are not required.
(1)

(e) Ethanol can be made from bromoethane by reaction with aqueous potassium hydroxide, KOH(aq), under suitable conditions.
      (i)   Write the equation for this reaction. State symbols are not required.
(1)

      (ii)  State the type and mechanism of this reaction.
(2)
Type
 ............................................................................................................................................. 
Mechanism
 ............................................................................................................................................. 
     (iii)  Suggest the formula of a suitable chemical to make ethanethiol from bromoethane.
(1)
 ............................................................................................................................................. 
(f) When ethanethiol undergoes complete combustion in air, a gas is produced which is not formed on the complete combustion of ethanol. Identify the gas and suggest why it is damaging to the environment.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for Question = 19 marks)

Unit 2 - Jan 2012
Q11.
Halogenoalkanes are important intermediates in organic chemistry. The scheme below summarises some important reactions of a halogenoalkane.

(a)  Identify the reagents and any specific conditions required for the reactions in the diagram. (You may assume that a suitable temperature is maintained in each reaction.)
(4)
A
 ............................................................................................................................................. 
B
 ............................................................................................................................................. 
C
 ............................................................................................................................................. 
D
 ............................................................................................................................................. 
(b)  (i)  Classify the type of reaction in each of A and D.
(2)
A
 ............................................................................................................................................. 
D
 ............................................................................................................................................. 
*(ii)  Reaction B can proceed via two possible reaction mechanisms, depending on the structure of the original compound. For each of the two isomers of C4H9Br shown below, draw the structure of the intermediate or transition state which is formed during the reaction. Explain in each case why the specified structure is more favourable.
(4)

Intermediate or transition state
Explanation
 ............................................................................................................................................. 
 ............................................................................................................................................. 

Intermediate or transition state
Explanation
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iii)  If C4H9I is used instead of C4H9Br in reaction D, the rate of formation of C4H9NH2 increases. Explain why the rate of reaction increases.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c)  Halogenoalkanes are widely used as refrigerants and belong to the class of refrigerants that cool by change of state (typically by boiling).
(i)  Suggest how halogenoalkanes cool by change of state.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

 (ii)  Suggest two characteristics or properties desirable in a refrigerant.
(2)
1
 ............................................................................................................................................. 
 ............................................................................................................................................. 
2
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(Total for question = 14 marks)

Q12.
When a chloroalkane is heated with aqueous sodium hydroxide
   A  no reaction occurs with primary, secondary or tertiary chloroalkanes.
   B  a reaction occurs with primary and secondary chloroalkanes but not with tertiary chloroalkanes.
   C  a reaction occurs with tertiary chloroalkanes but not with primary and secondary chloroalkanes.
   D  a reaction occurs with primary, secondary and tertiary chloroalkanes.
(Total for question = 1 mark)

Unit 2 - Jun 2012
Q13.

The steps below show the reaction mechanism for the reaction of a halogenoalkane with sodium hydroxide in aqueous solution to form an alcohol.

(a) (i) Name X and Z.
(2)
X
 ............................................................................................................................................. 
Z
 ............................................................................................................................................. 
(ii) Draw the skeletal formula of X.
(1)

(iii) What type of alcohol is Z?.
(1)
 ............................................................................................................................................. 
(b) (i) Name the mechanism and type of reaction shown above.
(2)
 ............................................................................................................................................. 
(ii) Explain what the curly arrows shown in the mechanism represent.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
*(iii) Suggest the shape of the intermediate Y. Explain your answer.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
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 (iv) If the reaction is carried out in alcoholic (ethanolic) rather than aqueous solution, a different type of reaction occurs and a different product is formed. Name the type of reaction that occurs in alcoholic (ethanolic) solution and identify the product by name or formula.
(2)
Type of reaction
 ............................................................................................................................................. 
Product

(c) The alcohol Z (shown below) resists oxidation. However, Z has three structural isomers which are readily oxidized. On complete oxidation, one isomer forms a ketone and the other two isomers form carboxylic acids.

(i) Draw the structural formula of the isomer of Z that forms a ketone.
(1)

(ii) Draw the structural formulae of the isomers of Z that form carboxylic acids.
(2)

(Total for question = 15 marks)

Unit 2 - Jun 2014
Q14.
(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)
 ............................................................................................................................................. 

(ii)  What type of reaction occurs in (a)(i)?
(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)
 ............................................................................................................................................. 
(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
 ............................................................................................................................................. 
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
 ............................................................................................................................................. 

Observation with A
 ............................................................................................................................................. 
(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)
 ............................................................................................................................................. 
(Total for Question = 11 marks)

Q15.
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)

Q16.
The compound with formula CH3CH(NH2)CH3 can be made by reacting alcoholic ammonia with

   A    propane.
   B    propene.
   C    2-chloropropane.
   D    propan-2-ol.
(Total for Question = 1 mark)

Unit 2 - Jun 2014
Q17.

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.
   B    oxidation.
   C    reduction.
   D    substitution.
(Total for question = 1 mark)

Q18.
This is a question about halogenoalkanes.
(a)  Halogenoalkanes can react with hydroxide ions in different ways depending on the conditions used. Using 1-chloro-1-fluoroethane, CH3CHClF, as an example of a halogenoalkane, the following reaction could occur in aqueous solution.
CH3CHClF + OH− → CH3CHOHF + Cl−
(i)  Suggest why it is unlikely that the fluorine atom in CH3CHClF would be substituted by the hydroxide ion.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

*(ii)  A student attempted to draw the reaction mechanism for the reaction in (a)(i), but made a total of three errors.

Identify these errors and state how they should be corrected.
(3)
First error
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Second error
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Third error
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(iii)  In hot alcoholic solution, a different reaction may occur between halogenoalkanes and hydroxide ions.
Write the equation for the reaction between 1-chloro-1-fluoroethane, CH3CHClF, and hydroxide ions in alcoholic solution.
(2)

(b)  Chloroethane can be produced in various ways as shown below. Identify, by name or formula, the reagent needed for each of these reactions.
(3)

(c)  (i)  Chloroethane will react with alcoholic ammonia initially to produce ethylamine. Complete the equation for this reaction.
(1)
.............................. + NH3 → .............................. + ..............................

(ii)  Name the type and mechanism of the reaction occurring in (c)(i).
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(iii)  What feature of the ammonia molecule enables the reaction in (c)(i) to take place?
(1)
 ............................................................................................................................................. 

(iv)  If aqueous ammonia was used in (c)(i), instead of alcoholic ammonia, suggest the identity of the organic product that would be formed.
(1)
 ............................................................................................................................................. 

(d)  Dichlorodifluoromethane, CCl2F2, is also known as Freon 12 and its manufacture was banned in 1994 under the terms of the Montreal Protocol.

(i)  Complete the equation for the initiation stage and suggest equations for two of the propagation stages and a termination stage for the mechanism of the reaction that this molecule might undergo with ozone.
(4)

Initiation           CCl2F2 →

Propagation 1

Propagation 2

Termination

*(ii)  Explain why the effect of Freon 12 molecules on the ozone layer was such a serious issue that scientists recommended its use to be discontinued.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(iii)  Freon 12, CCl2F2, could also be described as a "greenhouse gas". Explain what the term 'greenhouse gas' means.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(iv)  Freon 12, and other similar molecules, are not normally viewed as contributors to the greenhouse effect. Suggest why this is so.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (Total for question = 23 marks)

Q19.
The skeletal formulae of some 6-carbon bromoalkanes are shown below.
?
(a)  Which of the above bromoalkanes is not a structural isomer of the others?
(1)
   A    
   B    
   C    
   D    

(b)  Which of the above is not a secondary bromoalkane?
(1)
   A    
   B    
   C    
   D    
(Total for question = 2 marks)