Unit 2 – Green Chemistry
Unit 2 - Jan 2009
Questions
Q1.
Ethanoic acid is used industrially in the manufacture of polymers and glues and also in the food industry as an acidity regulator.
 It can be synthesized in the laboratory by the reaction of ethanol with excess sodium dichromate(VI) solution, acidified with concentrated sulfuric acid.  Ethanol is placed in a suitable flask along with some anti-bumping beads.  The concentrated sulfuric acid is then added a drop at a time.  The sodium dichromate(VI) solution is then added a drop at a time causing the mixture to boil spontaneously.  When the addition of the sodium dichromate(VI) solution is complete, the mixture is heated under reflux for approximately 15 minutes.  The ethanoic acid formed can then be separated from the reaction mixture.

Ethanoic acid can be produced industrially by the CativaTM process.  Methanol, which can be obtained from wood, is reacted with carbon monoxide in the presence of an iridium catalyst.

(a)  (i)   Balance the half-equation for the reduction of dichromate(VI) ions.
(1)

(ii)   The half-equation for the oxidation of ethanol is

Use this and your answer to (a)(i) to write a full equation for the overall reaction between acidified dichromate(VI) ions and ethanol.  State symbols are not required.
(2)

(b)  (i)   Why are the concentrated sulfuric acid and sodium dichromate(VI) added a drop at a time in the laboratory process?
(1)
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 (ii)   Draw a labelled diagram of the apparatus that could be used to heat the mixture under reflux.
(3)

(iii)   What colour would the mixture be after it was heated under reflux?
(1)
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(c)  A solution containing both water and ethanoic acid is produced by distillation of the final reaction mixture.
(i)   Explain why the other products and any excess reactants are left behind in the distillation flask.
(1)
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(ii)   Suggest a method to separate pure ethanoic acid, boiling temperature 118°C, from the water.
(1)
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 (d)  (i)   In the CativaTMprocess what effect, if any, would increasing the pressure have on the yield of ethanoic acid?  Justify your answer.
(2)
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 (ii)   Suggest TWO reasons why it might be difficult, or undesirable, to produce ethanoic acid in industry by scaling up the laboratory process.
(2)
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*(e)  An alternative industrial process for the production of ethanoic acid is the oxidation of butane using a transition metal catalyst at 150°C and 55−60 atm.

Evaluate the 'greenness' and sustainability of the two industrial processes.

 Suggest TWO additional pieces of information that would help you make a more informed decision.
(6)
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(Total for question = 20 marks)

Unit 2 - Jun 2009
Q2.

(a)  Draw a diagram to show the most significant intermolecular force between an ethanol molecule and a water molecule.  Label the bond angle between the molecules and state its value.
(2)

(b)  The student proposed to set up the apparatus as shown below to carry out the distillation to try to separate the ethanol from water.
    There are three errors with the set-up.  Draw a circle around each error.

        Describe what effect these errors would have if the student attempted to carry out the separation as shown.

        [Clamps are not shown in the diagram but you can assume the apparatus is supported adequately.]
(6)

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 (c)  If a balance is accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?
(1)

(d)  Suggest a suitable drying agent to absorb the water remaining with the ethanol after distillation.  Describe how you would use it to produce a dry sample of ethanol.
(2)
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(e)  Describe a chemical test you could carry out to confirm the presence of the −OH group in ethanol.  What result would you expect to see?
(2)
Test
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Result
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(f) *(i)  Explain what is meant by a carbon neutral fuel.
(2)
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*(ii)  Suggest TWO reasons why these biofuels may not be carbon neutral and describe TWO effects that large scale production of biofuels may have on society.  Which of the three biofuels do you think is the most sustainable? Justify your choice.
(5)
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(Total for question = 20 marks)

Unit 2 - Jan 2010
Q3.
This question is about some reactions of halogens and halide ions.
(a)  (i)  When chlorine is added to a solution containing bromide or iodide ions, a colour change occurs. What solvent would you add to the mixture to confirm the identity of the halogen produced?
(1)
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(ii)  Give the result for the test with this solvent in a reaction in which bromine is produced.
(1)
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(b)  (i)  Solid potassium bromide and potassium iodide can be distinguished by their reactions with concentrated sulfuric acid.
Potassium bromide reacts with concentrated sulfuric acid initially to produce hydrogen bromide. This reacts further, as shown below, to produce a sharp smelling gas and a brown fuming liquid.

Show, by use of oxidation numbers for sulfur, that the sulfuric acid has been
 reduced.
(2)
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 (ii)  State TWO observations, which would differ from those with potassium bromide, when potassium iodide reacts with concentrated sulfuric acid.
(2)
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 (iii)  One product of the reaction with potassium iodide is hydrogen sulfide, H2S. How does this show that iodide ions are more powerful reducing agents than bromide ions?
(1)
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 (c)  In areas where the natural concentration of fluoride ions in rocks is low, some water authorities add fluoride to the water supply to improve the dental health of children. An alternative would be to supply free fluoride tablets.
       Give ONE reason why it could be considered more ethical to supply free fluoride tablets rather than to add fluoride compounds to the water supply.
(1)
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 (Total for question = 8 marks)

Q4.

*(a)  Why are the bonds within a layer of carbon atoms in graphite stronger than the bonds between the layers of carbon atoms?
(2)
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 (b)  The data below gives the relative electrical conductivity of a pure graphite crystal.

Explain why the relative electrical conductivity of graphite differs with direction.
(2)
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 (c)  Suggest why the strength of the bond between the layers in graphite would increase if some carbon atoms were replaced with nitrogen atoms.
(2)
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 (d)  Suggest ONE benefit of using a light activated catalyst for the new process.
(1)
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 (e)  The liquid fuel, methanol, is made by reacting carbon monoxide with hydrogen.
Write an equation for this reaction. State symbols are not required.
(1)

*(f)  Benzene, which is needed for the new process of breaking down carbon dioxide, can be made from coal. It is now usually made by catalytic treatment of one fraction of crude oil at temperatures of around 500 °C and 20 atmospheres pressure.
Suggest the benefits and disadvantages of breaking down carbon dioxide using benzene and the catalyst as described in the passage. You should consider

·	the energy and resources needed
·	the effects on the atmosphere
·	whether it is a beneficial method for producing energy compared to direct use of fossil fuels. 
(6)
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 (g)  Carbon exists in forms other than graphite. Nanotubes are rolls of graphite layers, and fullerenes are cages of carbon atoms. Both nanotubes and fullerenes can trap other substances in their structures, and fullerenes can be coated with other substances.
Give ONE application of carbon nanotubes or fullerenes which exploits this behaviour.
(1)
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(Total for question = 15 marks)

Unit 2 - Jun 2010
Q5.
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)
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(ii)  Suggest the types of intermolecular force present between molecules of liquid halothane.
(2)
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 (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)
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 (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
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Structural formula
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(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)
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(ii)  Suggest ONE use for CFCs other than as a refrigerant.
(1)
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*(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)
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*(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)

Q6.
The use of poly(ethene) packaging has been criticised mainly because
   A     the complete combustion of poly(ethene) produces dangerous fumes.
   B     large amounts of oil are consumed in producing the monomer, ethene.
   C     poly(ethene) degrades to form toxic products.
   D     the catalyst used in the polymerization of ethene is expensive.
(Total for question = 1 mark)

Unit 2 - Jan 2011
Q7.
Which of the following best defines the meaning of the term anthropogenic change?
It is a change caused by
   A      nature.
   B      plants.
   C      animals.
   D      humans.
(Total for question = 1 mark)

Q8.

Which of the following statements is true?
   A      CFCs and nitrogen monoxide, NO, are involved in the depletion of the ozone layer.
   B      CFCs act as catalysts for the depletion of the ozone layer, while nitrogen monoxide, NO, does not.
   C      CFCs and ozone are free radicals.
   D      CFCs and nitrogen monoxide, NO, are decomposed by UV radiation.
(Total for question = 1 mark)

Q9.
This question is about some reactions which can be used in the manufacture of hydrogen.

       Reaction 1 uses two naturally occurring chemicals, water and natural gas. Steam is reacted with methane to form carbon monoxide and hydrogen in an equilibrium reaction.

       Reaction 1    CH4(g) + H2O(g)  CO(g) + 3H2(g)       ΔH = +210 kJ mol−1

       In reaction 2, carbon monoxide and steam are passed over copper at high temperature. This forms carbon dioxide and hydrogen.

       Reaction 2    CO(g) + H2O(g)  CO(g) + H2(g)

       The carbon dioxide formed is removed by passing it through potassium carbonate solution in reaction 3.

       Reaction 3    K2CO3(aq) + CO2(g) + H2O(l) → 2KHCO3(aq)

       The potassium carbonate is regenerated by heating the potassium hydrogencarbonate solution in reaction 4. The carbon dioxide gas produced is released into the atmosphere.

       Reaction 4    2KHCO3(aq) → K2CO3(aq) + CO2(g) + H2O(l)
(a) For each of the first three reactions, state the initial and final oxidation numbers of any elements that change their oxidation numbers. Hence decide which are redox reactions.
(5)
Reaction 1
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*(b) (i) Discuss, with reasons, the conditions of temperature and pressure that would favour the production of hydrogen in reaction 1. You should consider the effect of the conditions on both yield and rate.
(7)
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 (ii) Excess steam is used in reaction 1. State why an excess of a reagent is used and suggest why steam, rather than methane, is chosen.
(2)
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 (c) Copper is a catalyst in reaction 2. Explain how a catalyst increases the rate of a reaction.
(2)
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 (d) (i) State one economic advantage of reaction 4.
(1)
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*(ii) Reaction 4 contributes to global warming. Identify the substance formed in this reaction which is likely to be responsible and explain the processes that lead to an increase in global temperatures.

      Suggest two effects an increase in global temperatures might have on the environment.
(4)
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(Total for question = 21 marks)

Unit 2 - Jun 2011
Q10.
This question is about nitrogen monoxide, NO, which can be described both as a friend and a foe.

(a) (i)   What is meant by the term free radical?
(1)
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 (a) (ii)  Suggest a dot and cross diagram for nitrogen monoxide, showing outer shell electrons only, remembering that it is a free radical.
(2)

(b) (i)   Part of the unbalanced equation for the preparation of nitrogen monoxide from nitric acid is shown below.

Identify the elements which are oxidized and reduced and give their oxidation numbers.
(3)
Element oxidized .........................

Oxidation number initial .........................    final .........................

Element reduced .........................

Oxidation number initial .........................    final .........................

     (ii)  Complete and balance the equation for the reaction between silver and nitric acid.
(2)

(c) The reaction between nitrogen and oxygen to form nitrogen monoxide reaches equilibrium.

     (i)   Explain why the yield of nitrogen monoxide is increased when the temperature is increased.
(1)
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  ∗(ii)  State and explain the effect, if any, on the yield of nitrogen monoxide when the pressure is increased.
(2)
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   (iii)  State and explain how the rate of the reaction is affected by an increase in pressure.
(2)
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∗ (d) (i)  Explain why a jet aeroplane in flight causes much more damage to the ozone layer than cars carrying the same number of passengers at sea level. You should assume that the nitrogen monoxide outputs for both methods of conveying the passengers are the same.
(2)
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   (ii)  The reactions of chlorine free radicals with ozone may be represented by the following equations.

Write corresponding equations for the reactions of the free radical nitrogen monoxide with ozone. Combine your two equations to show the overall reaction.
Use these equations to explain why a small quantity of nitrogen monoxide can have a continuing effect on the ozone layer.
(5)
Equations

Explanation
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(Total for Question = 20 marks)

Q11.
The following reactions have been used in the chemical industry to make liquid and solid products, allowing any gaseous products to escape into the atmosphere:

(a) Which reaction has an atom economy by mass of 56%?
(1)
   A    
   B    
   C    
   D    

(b) Which reaction causes the most immediate damage to the environment?
(1)
   A    
   B    
   C    
   D    

(c) Which reaction is an electrophilic addition?
(1)
   A    
   B    
   C    
   D    
(Total for Question = 3 mark)

Unit 2 - Jan 2012
Q12.

(a) Write the equation for the formation of nitrogen monoxide from nitrogen and oxygen. State symbols are not required.
(1)

(b) The electronic structure of nitrogen monoxide is unusual in that it has an unpaired electron.
(i) What name is given to a chemical species such as nitrogen monoxide that has an unpaired electron?
(1)
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(ii) Chemical species with unpaired electrons occur as intermediates in some chemical reactions. What type of bond breaking produces these species?
(1)
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(c)(i) Suggest the most likely source of the hydrocarbons that react with nitrogen monoxide to form toxic compounds.
(1)
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(ii) Suggest the type of reaction that is involved when a hydrocarbon is converted into an aldehyde.
(1)
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(iii)  Draw the skeletal formula of the aldehyde with three carbon atoms.
(1)

(iv) By considering the equation

explain the effect of the reaction of hydrocarbons with nitrogen monoxide on the breakdown of ozone.
(1)
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(d) Suggest why the proportion of nitrogen dioxide might be reduced at high altitudes.
(2)
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 (e) Explain why it is important to maintain the concentration of ozone in the upper atmosphere.
(2)
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 (f)(i) Write an equation for the reaction on a catalytic converter described in the passage. State symbols are not required.
(1)

(ii) Draw an energy profile for the exothermic reaction in (f)(i). Label the axes, the reactants and products, the enthalpy change and the activation energy.
(3)

*(iii) By referring to your energy profile, explain how a catalyst speeds up a chemical reaction.
(3)
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 (g) Jet aircraft are considered a greater threat to the ozone layer than road vehicles. Suggest an explanation for this.
(2)
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 (Total for question = 20 marks)

Unit 2 - Jun 2012
Q13.
      Which of the following is not true? Chlorofluorocarbons, CFCs,
   A       are flammable.
   B       are greenhouse gases.
   C       damage the ozone layer.
   D       are excellent refrigerants.
(Total for question = 1 mark)

Q14.
(a)  Ozone, O3, is formed when oxygen is exposed to ultraviolet (UV) radiation or to an electric discharge. Ozone is a blue gas whereas oxygen is colourless. When the two gases are mixed, an equilibrium is established as shown in the following equation.
3O2(g)    2O3(g)      ΔH = +143 kJ mol−1
(i) When the temperature of the pale blue equilibrium mixture is increased at constant volume, the colour darkens. Explain this observation in terms of the changes to the equilibrium.
(2)
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 (ii) State and explain what you would see if the pressure of the system at equilibrium were increased.
(2)
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 (iii) A small amount of oxygen gas containing the isotope 18O is added to the equilibrium mixture. After a few hours, ozone containing 18O is detected. Given that the equilibrium position is not affected, explain this observation.
(1)
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 (b) The concentration of ozone in the atmosphere may be determined by bubbling air through a solution of acidified potassium iodide. Iodine is formed in solution, the concentration of which may be determined by titration with a solution of sodium thiosulfate of known concentration. The equations for the reactions are
O3 + 2I− + 2H+  →  O2 + H2O + I2     Equation 1
 I2+ 2S2O32−   →  2I− + S4O62−       Equation 2
In an experiment to determine the concentration of ozone in a sample of air, 100 m3 of air was bubbled through 100 cm3 of a solution containing an excess of acidified potassium iodide. The resulting solution was titrated against a solution of sodium thiosulfate of concentration 0.0155 mol dm−3. The volume of sodium thiosulfate solution required for complete reaction was 25.50 cm3.
(i) Calculate the number of moles of sodium thiosulfate that react.
(1)

(ii) Calculate the number of moles of iodine that reacted with the sodium thiosulfate.
(2)

(iii) Use equation 1 to deduce the number of moles of ozone that reacted with the acidified potassium iodide.
(1)

(iv) Calculate the volume of ozone, measured in m3, present in the original sample of air. Assume that all gas volumes were measured at room temperature and pressure and that the molar volume of any gas under these conditions is 0.024 m3 mol−1.
(1)

(v) Calculate the concentration of ozone in the sample of air in units of parts per million (ppm) by volume.
(1)

(vi) A student suggested that the 100 cm3 of acidified potassium iodide should be divided into four portions before the titration. Explain how this change increases the reliability and decreases the accuracy of the experiment.
(3)
Increases reliability
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Decreases accuracy
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 (c) Give the oxidation numbers of oxygen in equation 1, shown below. Hence state the role of ozone in this reaction.
(3)
O3 + 2I− + 2H+ → O2 + H2O + I2
Oxidation number of O
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Role of ozone
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(d) Ozone is used as an alternative to chlorine to disinfect flood damaged buildings, to remove residual smoke odours from fires and in the treatment of drinking water. Suggest one advantage of using ozone rather than chlorine, given that chlorine and ozone are both toxic.
(1)
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 (Total for question = 18 marks)

Q15.
Fuels of the Future
 Concerns about the future availability of fossil fuels, and the fact that their combustion produces greenhouse gases, have led to a search for alternative sources of energy. A great deal of attention has been directed at developing the use of hydrogen as a fuel. Since the only product of its combustion is water, hydrogen is considered to be a clean fuel.
However, the use of hydrogen has major drawbacks. The small size of the hydrogen molecule means that it is difficult to prevent leaks and, to store enough to provide a reasonable amount of fuel for a car, hydrogen must be compressed to around 700 atmospheres. Furthermore, the main source of hydrogen is currently fossil fuels such as methane, which is combined with steam in a series of reactions to form carbon dioxide and hydrogen.
One suggested alternative to hydrogen is ammonia. Ammonia, which is obtained by combining nitrogen and hydrogen at temperatures around 450°C and pressures of about 150 atmospheres, also has serious disadvantages: it is a toxic, corrosive and pungent gas which is difficult to ignite.
However, burning ammonia produces only nitrogen and water and it is relatively easy to liquefy, having a boiling temperature of just −33°C. Furthermore, the technology works: ammonia was used as a fuel for Belgian buses in the Second World War and, in 2007, the 'NH3 Car' project based in Ann Arbor, Michigan, used a mixture of ammonia and petrol to fuel a 2500 mile journey, from Detroit to San Francisco, in a modified pickup truck.
(a)  (i)  Explain the term greenhouse gas.
(2)
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*(ii) State and explain whether or not water (in the gaseous state) is a greenhouse gas.
(2)
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 (iii) Write the equation for the formation of hydrogen from methane and steam. State symbols are not required.
(2)

(iv) Suggest why using methane to form hydrogen in this way is preferable to burning methane directly.
(1)
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 (v) Storing hydrogen at a pressure of 700 atmospheres is a disadvantage to its use as a fuel because of the costs involved. Suggest why using such high pressures is so expensive.
(1)
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 (b)  (i)  Draw a dot and cross diagram for ammonia, showing the outer electrons only.
(1)

*(ii) By considering the intermolecular forces involved, explain why methane has a boiling temperature of 109 K while ammonia has a boiling temperature of 240 K, although these two compounds have very similar molar masses.
(4)
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 (c)  (i)  Write the equation for the combustion of ammonia. State symbols are not required.
(2)

(ii) The enthalpy change of combustion of methane is −890.3 kJ mol−1 and that of ammonia is −510.1 kJ mol−1. Suggest two additional items of information, not connected with environmental factors or the fact that methane is non-renewable, which would be useful in comparing methane and ammonia as fuels.
(2)
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(iii) The fact that ammonia has a pungent smell is listed as a disadvantage of its use as a fuel. Suggest why this might also be an advantage.
(1)
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 (iv) Suggest why ammonia was mixed with petrol in the 'NH3 Car' project.
(1)
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 (v) State, with a reason, whether hydrogen or ammonia can currently be considered to be long term replacements for fossil fuels.
(1)
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 (Total for question = 20 marks)

Unit 2 - Jun 2013
Q16.
The principal reason why scientists have recommended that chlorofluorocarbons (CFCs) are not used in aerosols is that they cause

   A    global warming.
   B    acid rain.
   C    ozone depletion.
   D    water pollution.
(Total for Question = 1 mark)

Q17.
Which of the following would not be used to assess whether the use of a biofuel produced from a crop of sugar cane is carbon neutral?
The amount of
   A    fuel used to operate farm machinery.
   B    pesticides and fertilisers used.
   C    energy released per tonne of biofuel.
   D    fuel used to process the crop.
(Total for Question = 1 mark)

Q18.
(a)  Sea water is a source of chemicals. The most abundant chemical dissolved in sea water is sodium chloride. Compounds of magnesium and bromine are also present. Magnesium occurs at 1300 parts per million (ppm) and bromine at 60 ppm by mass.

The solution left after crystallizing sodium chloride from sea water is even richer in bromine, and contains around 2.2 g dm−3 of bromine.

Bromine is extracted from this solution by passing in chlorine gas. The mixture is acidified to prevent hydrolysis of bromine by the reaction

Br2(aq) + H2O(l)  2H+(aq) + Br−(aq) + BrO−(aq)

The bromine can be separated by heating the solution to collect bromine vapour which is then condensed, or by blowing air through the solution.

(i)  Show by calculation that a solution containing 2.2 g dm−3 of bromine is richer in bromine than one containing 60 ppm.
[Assume that the mass of 1 dm3 of the bromine solution is 1000 g]
(1)

(ii)  Write an ionic equation, including state symbols, for the reaction in which chlorine gas reacts with bromide ions in solution to produce bromine.
(2)

(iii)  What would be observed when the reaction in (ii) occurs?
(1)
 ............................................................................................................................................. 
(iv)  Explain why the addition of an acid, such as hydrochloric acid, prevents hydrolysis of bromine.
(2)
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(v)  Assuming the hydrolysis of bromine is endothermic, explain how an increase in temperature would affect the equilibrium position for the hydrolysis of bromine.
(2)
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(vi)  Use your knowledge of activation energy to explain why an increase in temperature increases the rate of hydrolysis of bromine.
(1)
 ............................................................................................................................................. 

(vii) Use the equation for the hydrolysis of bromine to show that it is a disproportionation reaction.

Br2(aq) + H2O(l)  2H+(aq) + Br−(aq) + BrO−(aq)
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(b) At the surface of the sea, there is a dynamic equilibrium between carbon dioxide gas in air and dissolved carbon dioxide in the surface sea water.

CO2(g) CO2(aq)

(i)  State two features of a system which has reached dynamic equilibrium.
(2)
1.  .................................................................................................................................................... 
    ....................................................................................................................................................
2.  .................................................................................................................................................... 
    ....................................................................................................................................................

*(ii)  Carbon dioxide dissolves more easily in seawater than in pure water because seawater contains carbonate ions, CO32−(aq), and the following reaction occurs.

CO2(aq) + H2O(l) + CO32−(aq)  2HCO3 −(aq)

Explain how an increase in concentration of carbonate ions in sea water affects the amount of carbon dioxide gas in the atmosphere.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(iii)  Carbon dioxide and water vapour both contain polar bonds.
What effect does infrared radiation have on the bonds in these molecules?
(1)
 ............................................................................................................................................. 

*(iv)  Outline the mechanism by which molecules such as carbon dioxide and water cause global warming.
(2)
 ............................................................................................................................................. 
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*(v) Without water vapour in the atmosphere, the earth would be many degrees colder than it is at present. Why are many climate change scientists more concerned about warming due to carbon dioxide in the atmosphere, than warming due to the presence of water vapour? Refer to the difference between anthropogenic climate change and natural climate change in your answer.
(4)
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(Total for Question = 22 marks)

Q19.
It is important to lower the level of carbon dioxide in the atmosphere because of concerns over which environmental problem?
   A    Acid rain
   B    Global warming
   C    Non-biodegradability
   D    Ozone depletion
(Total for Question = 1 mark)

Q20.
A 'greener' chemical process will be one that
   A    uses energy less efficiently.
   B    forms a non-polluting waste product.
   C    produces significant amounts of waste.
   D    makes use of non-renewable resources.
(Total for Question = 1 mark)

Unit 2 - Jun 2014
Q21.
 One definition of the term 'carbon footprint' is
'the amount of carbon dioxide produced when a fuel is burned.'

Given the information above, what is the carbon footprint for paraffin in terms of grams of CO2 produced per MJ of energy?
   A    46
   B    56.09
   C    2580
   D    118 680
 (Total for question = 1 mark)

Q22.
Which of the following is a pure form of carbon that has both hexagonal and pentagonal rings in its structure and can conduct electricity?
   A    Charcoal
   B    Buckminsterfullerene
   C    Diamond
   D    Graphite
(Total for question = 1 mark)

Q23.
Insect-borne diseases, such as malaria, affect the lives of millions of people. Chemists are constantly finding new compounds to combat the transmission of these diseases. One such compound is the insect repellent commonly called p-menthane-3,8-diol (this is not its systematic name). It is used to protect both humans and animals.
The structure of p-menthane-3,8-diol is shown below.

p-menthane-3,8-diol is found naturally in the leaves of Eucalyptus citriodora, which is native to Australia and is commonly known as 'Lemon Bush'. It can be extracted from these leaves but is currently commercially prepared by chemical synthetic pathways. However, the commercially-made chemical has been found by some scientists to be less effective than the natural leaf extract.
It is possible that p-menthane-3,8-diol can kill microorganisms and it is this additional potential use and others which are being investigated by the chemical industry.
p-menthane-3,8-diol should not be confused with either methane or methanol.
(a)  p-menthane-3,8-diol has two alcohol functional groups. Classify the type of alcohol group on the far left of the structure drawn above and explain the meaning of the term 'functional group'.
(2)
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(b)  Give the molecular formula of p-menthane-3,8-diol.
(1)
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(c)  p-menthane-3,8-diol is found in the oily extract from the leaves of the 'Lemon Bush'.
One method used to extract the oil is described below.
Initially, the leaves are ground up using a pestle and mortar with some sand and an organic solvent, such as cyclohexane.
(i)  Suggest why sand is used.
(1)
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*(ii)  The solvent cyclohexane forms intermolecular forces with other organic molecules when they dissolve.
Identify these intermolecular forces and explain how they arise.
(3)
Type of intermolecular force
 ............................................................................................................................................. 

How they arise
 ............................................................................................................................................. 
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(iii)  How could the sand and other solid residue be removed from the mixture?
(1)
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(iv)  At this stage, either anhydrous magnesium sulfate or calcium chloride is added. Suggest the reason for this.
(1)
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*(v)  A student suggested using the following apparatus to remove the cyclohexane from the mixture.

Explain, in terms of the processes that occur in the above apparatus, why this method is unsuitable to remove the cyclohexane.
Suggest how this apparatus could be adjusted for a successful separation.
DATA
·	Boiling temperatures: p-menthane-3,8-diol 266 °C; cyclohexane 81 °C(4)
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(d)  Spectroscopic techniques can be used to confirm the presence and identity of organic molecules such as p-menthane-3,8-diol.
(i)  Suggest how infrared spectroscopy could be used to confirm the presence of the functional group in a molecule such as p-menthane-3,8-diol.
(1)
 ............................................................................................................................................. 

(ii)  Suggest the identity of two fragment ions, with a m/e value of more than 13 but less than 20, that could be observed in a mass spectrum of p-menthane-3,8-diol.
(2)
First fragment ion
 ............................................................................................................................................. 
Second fragment ion
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(e)  One reason why the synthetic p-menthane-3,8-diol may be less effective than the natural extract is because there are many isomers of this molecule.
Complete the structures below to show two structural isomers of p-menthane-3,8-diol which have the same number of alcohol functional groups and the same carbon skeleton.
(2)

*(f)  State two key principles of sustainability, and how the chemical industry might achieve these, when mass-producing a molecule such as p-menthane-3,8-diol.
(4)
Principle 1
 ............................................................................................................................................. 
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Principle 2
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(Total for question = 22 marks)

Q24.
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
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Second error
 ............................................................................................................................................. 
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Third error
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(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)
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(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)
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(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)
 ............................................................................................................................................. 
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(iii)  Freon 12, CCl2F2, could also be described as a "greenhouse gas". Explain what the term 'greenhouse gas' means.
(2)
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(iv)  Freon 12, and other similar molecules, are not normally viewed as contributors to the greenhouse effect. Suggest why this is so.
(1)
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(Total for question = 23 marks)