1 In recent years scientists have made tube-shaped structures of carbon called nanotubes.

(a)(i) State two differences between the structure of a carbon nanotube and the structure ofdiamond.

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(ii) Carbon nanotubes are fifty times stronger than steel.Use ideas about structure and bonding to suggest why these nanotubes are so strong.

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Multi-walled carbon nanotubes were first synthesised in bulk using the arc-vapourisation method. An electric current arc is passed to generate an arc between 2 graphite electrodes in the presence of helium gas at low pressure. The carbon nanotubes are found in the deposit of distilled carbon on the cathode. C60 and other fullerenes, which are also produced by this method, can be found together with a fluffy soot on the inside walls of the apparatus.

(b)(i) Why must the arc discharge generator be filled with an inert medium, such as helium gas?

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(ii) Why must nitrogen gas not be suitable for this purpose?

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Class Reg Number

Candidate Name .......................................................................

Chemistry H2 9746Tutor TuteeRevision Exercise 13: Integrated Questions

(iii) Nanotubes prepared in bulk inside the arc discharge chamber are often found to be adjacent to each other and aligned in long stiff bundles.

What type of intermolecular force is responsible for nanotube bundle formation?

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(iv) Energy calculations predict that arc discharge experiments should produce spherical fullerenes and not the less stable nanotubes.

In kinetic terms, briefly account for the formation of nanotubes under certain conditions in an arc discharge.

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(c) The figure below shows a molecule of buckminsterfullerene, C60.

List 2 similarities between the structures of an isolated single walled nanotube and a carbon-60 molecule.

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2 Sir James Jeans, who was a great populariser of science, once described an atom of carbon as being like six bees buzzing around a space the size of a football stadium.

(a)(i) Suggest what were represented by the six bees in this description.

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(ii) Explain (in terms of an atom of carbon) what stopped the bees from flying away from the space of the football stadium.

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(iii) What is missing from Jeans’ description when applied to an atom of carbon?

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(b) Crude oil is the principal source of hydrocarbons. The following are examples of such hydrocarbons.

Give the structural formulae of the organic products in the following reactions.

(i) The reaction of ethane with bromine in the presence of u.v. light.

(ii) The polymerisation of propene.

(iii) The oxidation of propene with cold, acidified potassium manganate(VII).

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(iv) The reaction of cyclohexene with hydrogen bromide.

(v) The reaction of cyclohexene with hot acidified potassium manganate(VII).

(b) Write equations for the following reactions.

(i) The complete combustion of ethane.

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(ii) The action of steam on propene in the presence of a catalyst.

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(iii) The reaction of cyclohexene with hydrogen in the presence of a catalyst.

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3 The ester 4-nitrophenyl ethanoate hydrolyses in alkaline solution according to the followingequation.

(a) Suggest, and briefly describe, a suitable experimental technique for studying the rate of this reaction.

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(b) The reaction rate was studied using two solutions of different hydroxide ion concentrations.

run A: [OH–] = 0.20 mol dm–3

run B: [OH–] = 0.40 mol dm–3

The following graphs show how the concentration of the ester, 4-nitrophenyl ethanoate, varied over time in the two runs.

(i) By drawing tangents on the graphs, measure and calculate the initial rates ofreaction during the two runs. Give the units in each case.

initial rate of run A ....................................................................................................

initial rate of run B ....................................................................................................

(ii) By using your results, calculate the overall order of reaction with respect to [OH–].

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(iii) From the curve of run B, determine the order of reaction with respect to [ester]. Explain your answer.

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(iv) Write a rate equation for the reaction.

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(v) Use your rate equation and the initial rates to calculate a value for the rate constant, including units.

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4(a) Barium ions are poisonous. Patients with digestive tract problems are sometimes given an X-ray after they have swallowed a ‘barium meal’, consisting of a suspension of BaSO4 in water. The [Ba2+(aq)] in a saturated solution of BaSO4 is too low to cause problems of toxicity.

(i) Write an expression for the solubility product, Ksp, for BaSO4, including its units.

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(ii) The numerical value of Ksp is 1.30 x 10–10. Calculate [Ba2+(aq)] in a saturated solution of BaSO4.

(iii) The numerical value of Ksp for BaCO3 (5 x 10–10) is not significantly higher than that for BaSO4, but barium carbonate is very poisonous if ingested. Suggest a reason why this might be so.

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(b) A useful commercial source of magnesium is sea water, where [Mg2+(aq)] is 0.054mol dm–3. The magnesium is precipitated from solution by adding calcium hydroxide.

Mg2+(aq) + Ca(OH)2(s) Ca2+(aq) + Mg(OH)2(s)

(i) Write an expression for the Ksp of Mg(OH)2, including its units.

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(ii) The numerical value for Ksp is 2.00 x 10–11. Calculate [Mg2+(aq)] in a saturated solution of Mg(OH)2.

(iii) Hence calculate the maximum percentage of the original magnesium in the seawater that this method can extract.

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(c)

(i)

The magnesium ions in seawater are mainly associated with chloride ions.

Use the following Hf values to calculate a value for the Hr of the following reaction.

MgCl2(s) Mg2+(aq) + 2Cl– (aq)

(ii) Use your answer to explain why MgCl2 is very soluble in water.

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(d) All the chlorides of Group II elements are soluble in water. The same is not true of their sulphates. These become less soluble as the group is descended. Explain qualitatively the variation in solubility of the sulphates of the elements in Group II down the Group from magnesium to barium.

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5 Compound G, in which R– represents the rest of the molecule, was made for use as a tear gas in World War 2.

Compound G was made by the following sequence of reactions.

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(a)(i) For stage I and for stage II, state the reagent(s) and condition(s) used to carry out each change.

stage I

reagent(s) ................................................................................................................................

condition(s) .............................................................................................................................

stage II

reagent(s) ................................................................................................................................

condition(s) .............................................................................................................................

(ii) Suggest the reagent(s) and condition(s) necessary to carry out stage III.

reagent(s) ................................................................................................................................

condition(s) .............................................................................................................................

Compound G was not actually used in World War 2 and stocks of it had to be destroyed safely. The following sequence of reactions was used in this process.

(b)(i) For stage IV and for stage V state the reagent(s) and condition(s) necessary to bring about each reaction.

stage IV

reagent(s) ................................................................................................................................

condition(s) .............................................................................................................................

stage V

reagent(s) ................................................................................................................................

condition(s) .............................................................................................................................

(c) The full sequence of stages I to VI involves some compounds which contain chiral centres.

(i) Explain what is meant by the term chiral centre.

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(ii) Draw displayed formulae for the isomers of one compound in the full sequence of stages I to VI which you consider to be chiral.

6 The unsaturated hydrocarbon ethyne (acetylene), C2H2, is widely used in ‘oxy-acetylene torches’ for cutting and welding metals. In the torch, ethyne is burned in oxygen to produce a flame with a temperature of 3400 K.

(a) Ethyne is a linear molecule with a triple bond, CC, between the two carbon atoms.Draw a ‘dot-and-cross’ diagram of an ethyne molecule.

(b) When used for cutting or welding, ethyne is transported in cylinders which contain the gas under pressure. A typical cylinder has a volume of 76 dm3 and contains ethyne gas at 1515 kPa pressure at a temperature of 25 °C.

Use the general gas equation, pV = nRT, to calculate the amount, in moles, of ethyne in this cylinder.

(c) In some countries, ethyne is manufactured from calcium carbide, CaC2, which is produced by heating quicklime and coke together at 2300 K.

CaO + 3C CaC2 + CO

When water is added to the CaC2, calcium hydroxide, Ca(OH)2, and ethyne, C2H2, are produced.

(i) Construct a balanced equation for the formation of ethyne from calcium carbide.

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(ii) Use this equation and your answer to part (b) to calculate the mass of CaC2 which will react with an excess of water to produce enough ethyne to fill 100 cylinders of the gas.

(d) The equation for the complete combustion of ethyne is given below. Use appropriate bond energy data from the Data Booklet to calculate a value for the enthalpy change of combustion of ethyne.

C2H2(g) + ⁵⁄₂O2(g) 2CO2(g) + H2O(g)

(e) The value for the standard enthalpy change of combustion of ethyne is –1300 kJ mol–1.

(i) Define the term standard enthalpy change of combustion.

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(ii) Explain why your answer to (d) does not have the same value as the standard enthalpy change of combustion.

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7 Monuments made of marble or limestone, such as the Taj Mahal in India and the Mayan temples in Mexico, are suffering erosion by acid rain. The carbonate stone is converted by the acid rain into the relatively more soluble sulphate.

CaCO3(s) + H2SO4(aq) CaSO4(s) + H2O(l) + CO2(g)acid rain

(a)(i) Write an expression for the solubility product, Ksp, of CaSO4, stating its units.

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(ii) The Ksp of CaSO4 has a numerical value of 3 x 10–5. Use your expression in (i) to calculate [CaSO4] in a saturated solution.

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(iii) Hence calculate the maximum loss in mass of a small statue if 100 dm3 of acid rain falls on it. Assume the statue is made of pure calcium carbonate, and that the acid rain becomes saturated with CaSO4.

(b) The life of such monuments is now being extended by treating them with a mixture of urea and barium hydroxide solutions. After soaking into the pores of the carbonate rock, the urea gradually decomposes to ammonia and carbon dioxide. The carbon dioxide then reacts with the barium hydroxide to form barium carbonate.

(NH2)2CO(aq) + H2O(l) 2NH3(g) + CO2(g)Ba(OH)2(aq) + CO2(g) BaCO3(s) + H2O(l)

Acid rain then converts the barium carbonate to its sulphate.

BaCO3(s) + H2SO4(aq) BaSO4(s) + H2O(l) + CO2(g)

Barium sulphate is much less soluble than calcium sulphate. A saturated solution contains [Ba2+] = 9.0 x 10–6mol dm–3.

(i) Explain why barium sulphate is less soluble than calcium sulphate.

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(ii) Write an expression for the Ksp of barium sulphate and use the data to calculate its value.

(c)(i) Explain what is meant by the term lattice energy.

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(ii) Predict, with a reason, how the lattice energy of BaSO4 might compare with that of MgSO4.

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8 During the early 1970s nearly one million tonnes of CFCs were being manufactured annually. Uses included blowing agents for making foam, cleaning agents, propellants and as a component of air conditioning units.

(a) Give three physical or chemical properties relevant to their use in these applications.

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(b) Using appropriate equations, describe how CFCl3 (CFC-11) can be involved in the destruction of the ozone layer. Explain why a single molecule of CFC may destroy many molecules of ozone.

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(c) CFCs may be classified according to both their global warming potential (GWP) relative to carbon dioxide and their ozone depletion potential (ODP) relative to CFCl3. The global warming potential is usually quoted to cover a specified period of time.

The table below summarises this information for CFCl3 and CF2Cl2 (CFC-12).

(i) Suggest why CF2Cl2 has a greater value for its ODP.

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(ii) Suggest why there is a difference in the 20 year and 100 year GWP figures for CFCl3 but not for CF2Cl2.

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.................................................................................................................................................(d) The CFCs used in air conditioning units have now been almost entirely replaced by

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compounds such as CF3CHCl2 (HCFC-123).

Explain why this compound is considered to be preferable to CFCl3.

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9 Sulphuric acid is a strong dibasic acid, which ionises in solution as follows.

(a) The organic base guanidine contains carbon, nitrogen and hydrogen. Its reaction with acids can be represented as follows.

where B represents the molecule of guanidine.

When a 25.0 cm3 sample of dilute sulphuric acid was titrated against a solution of guanidine, the following titration curve was obtained.

Use this curve to answer the following questions.

(i) Is guanidine a strong or a weak base? Explain your answer.

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(ii) The pH at the start of the titration was 0.70. Calculate the [H+], and hence the concentration of sulphuric acid, at the start of the titration.

(iii) Calculate the concentration of guanidine in the solution in mol dm–3.

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(iv) The guanidine solution contained 8.68 g of the base per dm3. Use your answer to (iii) calculate the Mr of guanidine.

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(b) One of the major industrial uses of sulphuric acid is to convert phosphate rock (calcium fluorophosphate(V)) into ‘superphosphate’ for use as a fertiliser. The process can be represented by the following partially balanced equation.

(i) Balance the above equation.

(ii) Use your balanced equation to calculate the mass of H2SO4 required to manufacture 1.0 kg of superphosphate fertiliser.

(c) Solutions of hydrogenphosphates make useful buffers for biochemical experiments.

(i) Explain what is meant by the term buffer solution.

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(ii) Calculate the pH of a buffer solution that contains 0.20 mol dm–3 NaH2PO4 and 0.10 mol dm–3 Na2HPO4. [Ka (H2PO4

–) = 6.3 x 10–8 mol dm–3]

10 Ibuprofen is one of the most commonly used non-steroidal anti-inflammatory drugs, used to

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treat chronic arthritic pain caused by inflammation of the joints.

(a)(i) Draw a circle around any chiral centre(s) in the above structure.

(ii) Write down the molecular formula of ibuprofen.

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(iii) Calculate the Mr of ibuprofen and use it to calculate how many grams are needed to make 100 cm3 of a 0.15 mol dm–3 solution.

(iv) Vigorous oxidation of ibuprofen produces a dibasic acid A. A solution containing 0.10 g of A required 12.0 cm3 of 0.10 mol dm–3 NaOH for neutralisation.

Suggest a structure for A, showing your working.

(b) The Ka value for ibuprofen is 6.3 × 10–6 mol dm–3.

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(i) Write an expression for Ka.

(ii) Use the Ka value to calculate the pH of a 0.15mol dm–3 solution of ibuprofen.

(c) To avoid problems with digestive irritation over a long period of use, research is being carried out into ways of administering ibuprofen using skin patches. For this use the compound is dissolved in a hydrophilic gel which acts as a buffer.

(i) What do you understand by the term buffer?

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The buffer used in the pharmaceutical preparation is a solution containing Na2HPO4 and NaH2PO4. These salts contain the HPO4

2– and H2PO4– ions respectively.

(ii) Write equations to show how this buffer reacts with

H+ ions, ...................................................................................................................................

OH– ions. ................................................................................................................................

(iii) A buffer solution containing equal concentrations of the two sodium phosphate salts has a pH of 7.20.

Calculate the pH of a pharmaceutical preparation containing 0.002mol dm–3 of Na2HPO4

and 0.005mol dm–3 of NaH2PO4.

End of Paper

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