S 7C Carmel Secondary School Date: 23 Feb., 2005 Final Examination (04-05) Time allowed: 3 hrs.

Name:_________________ ( ) Chemistry (Paper 2) Total no. of pages:10 Total mark: 100

Instructions:1. There are TWO sections in this paper, Section A and Section B.2. Section A carries 60 marks and Section B carries 40 marks.3. Answer THREE questions from Section A and TWO questions from Section B.4. Answers to questions in Section A and B are to be written in the single-lined

paper.5. Some useful constants and a Periodic Table are respectively printed on page 10 of

this question paper.

Section AAnswer any THREE questions.

1 (a) (i) By means of a balanced chemical equation, including state symbols, illustrate the term the average C-H bond energy in methane.

(ii) Hydrogen is used in large quantities in industry to convert nitrogen into ammonia, for use in fertilizers. One method of manufacturing hydrogen is to pass methane and stream over a heated nickel catalyst.

CH4(g) + H2O(g) CO(g) + 3H2(g) H1=+206 kJ mol-1

(1) Use the value of H1 above, and bond energy values to calculate the total bond energy in the carbon monoxide molecule.

(2) Suggest why the bond energy you have calculated in (i) is larger than either of the carbon-oxygen bond energies given.

The carbon monoxide is further reacted with more steam over a copper/zinc catalyst.

CO(g) + H2O(g) CO2(g) + H2(g) H2=+41 kJ mol-1

(3) Suggest and explain a method whereby the carbon dioxide could be removed from the product gas stream.

(Bond energies: E(C-H) = + 412 kJ mol-1, E(O-H) = + 463 kJ mol-1,E(H-H) = + 436 kJ mol-1, E(C-O) = + 437 kJ mol-1

E(C=O) = + 744 kJ mol-1 )(10 marks)

(b) (i) Explain how and why the presence of a catalyst affects the rate of a chemical reaction.

(ii) State and explain how the rate constant k1 and k2 for the forward and reverse reactions and the equilibrium constant Kc for the reaction

CHMS7Y04E1P2 P.1

H2(g) + I2(g) 2HI(g) H is positivewould change, (1) in the presence of a catalyst.(2) with an increase in temperature.

(iii) Give a brief account of the use of catalysts in industry, referring to the manufacture of ONE inorganic and ONE organic compound in your answer.

(6 marks)

(c) From the elements in the block Sc to Zn,(i) give the formula of the ion of an element in the +2 oxidation state

which contains four unpaired electrons in the ground state and is relatively easy to oxidize to the +3 oxidation state;

(ii) give the symbol for an element forming only one oxidation state, and explain why only this single oxidation state is known;

(iii) give the formula of the ion containing a metal having the highest oxidation state and state the oxidation state of the metal in this ion.

(4 marks)

2 (a) (i) (1) The following table lists the boiling points of some compounds of hydrogen. By reference to the type and extent of relevant intermolecular forces, explain as fully as you can the differences in boiling points between A and B, between B and C, and between A and D.

Compound Formula B.p. (oC)A Methane CH4 -164B Ammonia NH3 -33C Water H2O 100D Silane SiH4 -112

(2) Use the explanations you have given in (1) to predict boiling points for hydrogen fluoride, HF, and for germanium hydride, GeH4.

(ii) Honey contains 20% of water by mass, all of which is bound of sugar molecules by intermolecular forces.Assume the sugar contained in honey consists entirely of glucose, C6H12O6. A simplified structure is given below.

CHMS7Y04E1P2 P.2

(1) Calculate the average number of water molecules bound to each molecule of glucose in the honey, assuming the honey contains glucose and water only.

(2) What type of intermolecular force is likely to be responsible for the binding of water to glucose? Illustrate your answer with a diagram based on the above figure of glucose, showing clearly which atoms take part in the intermolecular interaction.

(12 marks)

(b) The water of Lake Nakuru in the Kenyan rift valley contains dissolved sodium carbonate and sodium hydrogencarbonate. The following equilibrium exists:

HCO3-(aq) H+(aq) + CO3

2-(aq)(i) Explain how this solution acts as a buffer on the addition of either

acid or alkali.

(ii) The pH of Lake Nakuru is 10.3 and the ratio is 0.958.

Calculate the equilibrium constant for the above reaction.

(iii) When 10.0 cm3 of lake water were titrated with 0.20 mol dm-3 HCl, 22.0 cm3 of acid were required to neutralize all carbonate and hydrogencarbonate ions according to the following equations:

H+(aq) + HCO3-(aq) H2O(l) + CO2(g)

2H+(aq) + CO32-(aq) H2O(l) + CO2(g)

Calculate the total number of moles of acid used, and thus, by using the ratio quoted in part (ii), calculate [HCO3

-(aq)] and [CO32-(aq)] in the lake.

(8 marks)

3 (a) (i) Helium has a triple point of 1.0 K, 0.05 x 105 Pa. Moreover, solid helium has the same density as liquid helium.Sketch and label the phase diagram of helium. Explain the slope of the solid-liquid equilibrium line on your phase diagram.

(ii)What is the meaning of “Triple point”?(iii)State and explain the difference between the heating of solid helium on

the moon and on the earth.(7 marks)

(b) (i) From the s-block elements (Group I and II), give the symbol for the element which reacts most vigorously with water and give an equation for the reaction.Suggest why this element reacts most vigorously with water.

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(ii) How do the solubilities of the hydroxides in Group II vary down the group?

(3 marks)

(c) (i) Give an account of the redox chemistry of the anions of nitrogen and sulphur. Your answer should include reference to the chemistry of NO2

-, NO3-, S2-, SO3

2-, S2O32- and S2O8

2-. You should consider the relative stabilities of the various oxidation states exhibited by nitrogen and sulphur, and include a range of reactions to illustrate your account. Marks will be gained for properly balanced equations.

(ii) When a heavy metal nitrate is heated to produce the metal oxide, nitrogen dioxide and oxygen, the nitrogen dioxide and oxygen are always produced in the ratio of 4:1. By considering the oxidation state changes of the nitrogen and the oxygen, show why this should be so, and hence write an equation for the thermal decomposition of aluminium nitrate.

(10 marks)

4. (a) This question concerns the elements boron, aluminium and gallium, which are found in Group 3 of the Periodic Table. Their electronic structures are:

Boron 1s22s22p1

Aluminium 1s22s22p63s23p1

Gallium 1s22s22p63s23p63d104s24p1

(i) (1) State the acid-base character of boron oxide and of aluminium oxide.

(2) Why is the acid-base character of aluminium oxide of industrial importance?

(ii) (1) Sketch the molecular shapes of BCl3 and Al2Cl6 at the temperature of vaporization.

(2) Suggest why boron does not form B2Cl6 at room temperature.(6 marks)

(b) (i) State Le Chatelier’s principle.(ii) Many commercially important processes involve equilibrium

reactions. Give TWO examples of such processes, naming each process and giving the appropriate equation(s).

(iii) In the Mond process for the purification of nickel, carbon monoxide is passed over impure nickel at 50oC to form, at this temperature, gaseous nickel tetracarbonyl, Ni(CO)4. This vapour is then passed over pure nickel pellets at 230oC. When the nickel tetracarbonyl decomposes, pure nickel will be deposited.

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(1) Write the equation for the formation of nickel tetracarbonyl.(2) Give the expression for Kc for the reaction in (1).(3) If the concentration of CO(g) in an equilibrium mixture is

doubled, calculate the change in the nickel tetracarbonyl concentration.

(4) Hence suggest a reason why a new Canadian plant operates at elevated pressure of 20 atmospheres in the first stage, compared with the atmospheric pressure of older plants.

(9 marks)

(c) In the hydrolysis of CH3Br, which is a second order reaction, the rate of reaction at 60oC was found to be 8.13x10-5 mol dm-3 s-1 when the concentration of hydroxide ion and CH3Br were 0.2 and 0.05 mol dm-3 respectively.

(i) Give the rate equation for the reaction and calculate the rate constant at 60oC.

(ii) At 80oC the rate constant was measured as 50.0 x 10-3 mol-1 s-1. Calculate the activation energy, E for the hydrolysis using the

Arrhenius’ equation which may be written as ln k = ln A -

(R = 8.31 J K-1 mol-1)(5 marks)

CHMS7Y04E1P2 P.5

Section BAnswer any TWO questions.

5. (a) Many organic reactions can be classified as either substitution, elimination, oxidation or reduction reactions. Their mechanisms can also be classified as either nucleophilic, electrophilic or free radical.

Suggest reagents and conditions for each of the following transformations, and classify them as far as you can according to the above groupings.

(i) CH3CH=CH2 CH3CHBrCH3

(ii) CH3CH2CH3 CH3CHBrCH3

(iii) CH3CHBrCH3 CH3CH(OH)CH3

(iv) CH3COCH3 CH3CH(OH)CH3

(8 marks)

(b) For a smoother-running car engine, it is important that the fuel/air mixture can be fully compressed before it is ignited. In order to achieve this, tetraethyl-lead, Pb(C2H5)4, has been added to petrol for many years.(i) (1) Suggest what sort of chemical bond exists between the lead and

each ethyl group. (2) What is the shape of the tetraethyl-lead molecule?

(ii) At the temperature of a car engine, the tetraethyl-lead molecule breaks up into two main components. Suggest their identities (in words or formulae).

(iii) Write a balanced equation for the complete combustion of tetraethyl-lead.

(iv) (1) Which one of the combustion products in (iii) is likely to cause damage to the moving parts of the car engine?

(2) In order to prevent this damage, 1,2-dibromoethane is added to leaded petrols.Suggest the formula of the substance containing bromine which is now emitted in the exhaust fumes.

(3) Why is this exhaust emission undesirable?(v) In 1972, before unleaded petrols were available, 1.0 x 1012 liters

(dm3) of petrol were used by vehicles. On average, each liter of petrol contained 0.60 g of tetraethyl-lead.Calculate, in kg, the mass of lead that was emitted from car exhaust pipes in that year.

(8 marks)

(c) Indicate how you could distinguish between each of the following pairs of substances using only simple chemical tests, giving the results of the tests in each case. Account briefly for the observed differences for each pair.

CHMS7Y04E1P2 P.6

(i) CH3COCH2CH2CH3 and CH3CH2COCH2CH3

(ii)

(4 marks)

6. (a) Discuss the bonding forces in each of the following substances and show how the magnitude of these forces between particles is reflected in physical properties.

(i) ethanol(ii) cis- and trans-butenedioic acids(iii) ethane

(6 marks)

(b) A secondary alcohol P, (C4H10O) can be dehydrated to give two isomeric alkenes, Q and R, one of which (Q) can exhibit geometrical isomerism. Q reacts with hydrogen bromide to give S, which can undergo the following sequence of reactions.

(i) Name a reagent which could bring about dehydration of P.(ii) (1) Draw the structure of P.

(2) Draw the structures of the geometrical isomers of Q.

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(3) Explain why Q can exist as geometric isomers.(iii) Give the reagents and conditions required for steps 2, 3 and 4.(iv) (1) Show the mechanism of the reaction of Q with hydrogen

bromide.(2) Step 2 proceeds by an SN2 mechanism. Show this mechanism in

full.(v) State, giving an explanation, whether or not S would be chiral.

(14 marks)

7 (a) The compound A (pentyl 4-methoxycinnzmate) is used in some sun-screen creams to protect the skin from burning in ultra-violet rays from the sun. The formula of A is:

(i) (1) Name three functional groups present in A.(2) Describe a test to show the presence of unsaturation in this

molecule. Give reagents, conditions and an equation for this reaction as well as the observable result.

(ii) Give the structures of the organic products formed when A undergoes the following reactions.

(1) Heating under reflux with alkaline KMnO4, followed by acidification.

(2) Heating with hydrogen in the presence of a nickel catalyst.(3) Heating under reflux with aqueous sodium hydroxide.

(iii) Two isomeric forms of the compound A exist. Give the structures of these two isomers, state the type of isomerism and explain briefly how it occurs.

(iv) Explain briefly what environmental changes are occurring which may require an increase in the use of such sun-screen creams in the future.

(11 marks)

(b) On hydrolysis, a tripeptide produced the following amino acids in equi-molecular amounts.

Amino acid B Amino acid C Amino acid D

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(i) In how many different ways can these three amino acids be coupled by peptide bonds to form a tripeptide?

(ii) Draw the structural formula of one such tripeptide.Indicate what happens when the tripeptide is dissolved, without hydrolysis, in(1) dilute aqueous sodium hydroxide;(2) dilute hydrochloric acid.

(iii) Describe simple tests to distinguish amino acids B, C and D. (6 marks)

(c) Suggest a synthetic route, in not more than three steps, for the transformation of propylbenzene to N,N-diethylbenzamide.

(3 marks)

End of paper

CHMS7Y04E1P2 P.9

Useful Constants

Gas constant, R = 8.31 J K-1 mol-1

Faraday constant, F = 9.65 x 104 C mol-1

Avogadro constant, L = 6.02 x 1023 mol-1

Plank constant, h = 6.63 x 10-34 JsSpeed of light in vacuum, c = 3.00 x 108 ms-1

Ionic product of water at 298 K, Kw = 1.00 x 10-14 mol2 dm-6

Specific heat capacity of water = 4.18 J g-1 K-1

Characteristic Infra-red Absorption Wavenumber RangesBond Compound type Wavenumber range /cm-1

C=C Alkenes 1610 to 1680C=O Aldehydes, ketones, carboxylic acids, esters 1680 to 1750C C Alkynes 2070 to 2250C N Nitriles 2200 to 2280O-H Acids (hydrogen-bonded) 2500 to 3300C-H Alkanes, alkenes, arenas 2840 to 3095O-H Alcohols, phenols (hydrogen-bonded) 3230 to 3670N-H Amines 3350 to 3500

CHMS7Y04E1P2 P.10

S 7C Carmel Secondary School Date: 23 Feb., 2005 Final Examination (04-05) Time allowed: 3 hrs.

Name:_________________ ( ) Chemistry (Paper 1) Total no. of pages:10 Answer Total marks: 100

1(a) (i) CH4(g) C(g) + 4H(g) H (1)

BE(C—H) = H (1)

(ii) CH4(g) + H2O(g) CO(g) + 3H(g) H1 = +206 kJ/mol (1)

(1) BE (reactants) = 4 BE (C—H) + 2 BE (O—H) (1)= (4 412) + (2 463) = 2 574 kJ (1)

BE (products) = 1 BE (CO) + 3 BE (H—H) (1)= BE (CO) + (3 436)= BE (CO) + 1 308

H (reaction) = BE (reactants) – BE (products)+206 = 2 574 – [BE (CO) + 1 308] (1)

BE (CO) = +1 060 kJ/mol

(2) Bond in CO is CO, a triple bond. It is much stronger than C—O and C=O. (1)

(3) Pass mixture of CO2 and H2 over aq. KOH. (1)Acidic gas CO2 dissolves in alkaline KOH: (1)

CO2 + 2OH– CO32– + H2O

(b)(i) The presence of catalyst will increase the rate of reaction by providing a low Ea path for the reaction to occur. (2)

(ii) k1 k–1 K(1) catalyst increase increase unchanged (1)(2) Increase in temperature increase increase increase (1)

less than k1

(iii) Manufacture of NH3 from N2 and H2 (Haber’s process) (1)Catalyst — finely divided iron

Hydrogenation of ethene to give ethane (1)Catalyst — finely divided nickel

(c) (i) Cr2+ Cr3+

[Ar] 3d4 [Ar] 3d3 (1)

(ii) Sc Sc3+

[Ar] 3d1 4s2 [Ar] (1)Sr3+ has a stable octet configuration. (1)

CHMS7Y04E1P2 P.11

(iii) MnO4– (+7) (1)

2. (a) (i)(1) A: CH4, non-polar molecule (1)Discrete molecules held together by weak instantaneous dipole — induced dipoles very low bp. (1)

D: SiH4 similar to AWeak intermolecular force (instantaneous dipole — induced dipoles) very low bp. (1)Since SiH4 has more electrons than CH4, the strength of intermolecular forces is stronger. bp of it is higher than CH4. (1)B: NH3 — polar molecule with highly electronegative atom N. Strong H-bonding between NH3 molecules bp is higher than A and D. (1)

C: H2O — polar molecule has highly electronegative atom O. H-bonding between H2O molecules is stronger than NH3 because O is more electronegative than N. (1)Hence bp of H2O is higher than NH3.

(2) bp of H2O > bp of HF > bp of NH3

(forms more H (F morebonds than HF) electronegative than N)

bp of GeH4 > bp of SiH4 (2)GeH4 has more electrons. stronger Van der Waal’s forces.

(ii) (1) C6H12O6 H2O% by mass 80 20Mr 180 18Rel. no. of moles

Ratio 1 : 2.5(2)

(2) H-bonds (1)

(1)

CHMS7Y04E1P2 P.12

2. (b) (i) CO32– remove additional H+ from added acid: (1)CO3

2– + H+ HCO3–

HCO3– removes additional OH– from added alkali: (1)

HCO3– + OH– CO3

2– + H2O

(ii) K = [H+]

pH = 10.3 [H+] = 5.012 10–11 mol/dm3 (1)K = (5.012 10–11) 0.958

= 4.80 10–11 mol/dm3 (1)

(iii) moles HCl = 0.2 = 0.004 4

(1)Let [HCO3

–] = a mol/dm3 [CO32–] = 0.958a

[H+] = a [H+] = 2 0.958a

moles [H+] = a moles [H+] = 2 0.958a

(1)

Total [H+] = a(1 + 2 0.958) = 0.004 4

(1)a = [HCO3

–] = 0.151 mol/dm3

[CO32–] = 0.145 mol/dm3 (1)

3 (a)(i)

(2)

The solid-liquid equilibrium line is vertical since the volume of solid and liquid (1)

He is the same for a fixed mass of He, i.e. pressure has no effect on mp. (1)

(ii) Three phases coexist and at equilibrium. (1)

(iii) The pressure on the moon is lower than the triple point. Therefore, solid will sublime. (1)However, the pressure on the earth is higher than the triple point. Solid will change to liquid first and then to vapour. (1)

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(b) (i) 2Cs + 2H2O 2CsOH + H2 (1)Cs is the most metallic of all the Groups I and II elements. (1)

(ii) Group II metallic hydroxides become more soluble down the group. (1)

(c) (i) NO2– — reducing and oxidising properties

As a reducing agent, it is oxidised from +3 to +5 (NO3–).

e.g. 2MnO4– + 5NO2

– + 6H+ 2Mn2+ + 5NO3– + 3H2O

As an oxidising agent, it is reduced from +3 to +2 (NO).e.g. 2I– + 2NO2

– + 4H+ I2 + 2NO + 2H2O(2)

NO3– — very weak oxidising property, oxidised by strong reducing agents.

e.g. nascent H2 (Devorda alloy + NaOH).NO3

– is reduced from +5 to –3 (NH3).NO3

– + 4Zn + 7OH– + 6H2O NH3 + 4Zn(OH)42–

(2)S2– — (H2S) reducing; oxidised from –2 to 0 (sulphur)e.g. 2H2S + SO3

2– + 2H+ 3H2O + 3S(1)

• SO32– – reducing property; oxidised from +4 to +6 (SO4

2–)e.g. OCl– + SO3

2– Cl– + SO32–

(1)• S2O3

2– — reducing; oxidised to S4O62– or SO4

2–

e.g. 2S2O32– + I2 2I– + S4O6

2–

e.g. 4Cl2 + S2O32– + 5H2O 8Cl– + 2SO4

2– + 10H+ (1)

• S2O82– — strong oxidising agent; reducing to SO4

2–(+6)e.g. Mn2+ +S2O8

2– + 2I– I2 + 2SO42– (1)

(ii) e.g. Mg(NO3)2 MgO + 4NO2 + O2

Decrease in oxidation no. of one N: +5 to +4 = –1Increase in oxidation no. of two O: 2(–2) to 0 = +4 Ratio NO2 to O2 = 4 : 1 (2)

4. (a) (i) (1) B2O3 — acidic (1/2)Al2O3 — amphoteric (1/2)

(2) Al2O3 dissolves in both acids and alkalis. Thus, aluminium can be separated from other impurties. (1)

(ii) (1) (2)

(2)

CHMS7Y04E1P2 P.14

(2) BCl3 does not dimerise at room temperature because of the small size of the B atom which may not be able to fit 4 big Cl atoms around it in the dimer. (2)

(b) (i) Le Chatelier’s principle states that if a system in equilibrium is subjected to a change, the equilibrium position of the system will shift in a way to minimize the effect of the change. (2)

(ii) Haber’s Process: N2(g) + 3H2(g) 2NH3(g) (1)Manufacture of H2SO4:SO2(g) + O2(g) SO3(g)SO3(g) + H2SO4(l) H2S2O7(l)H2S2O7(g) + H2O(l) H2SO4(l) (2)

(iii)(1) Ni(s) + 4CO(g) Ni(CO)4(g) (1)

Kc = (1)

(2) [CO] is doubled.[Ni(CO) 4] increases by 24 = 16 times. (1)

(3) At 20 atm, [CO] increases. This shifts equilibrium in the direction of Ni(CO)4 and increase the yield of Ni(CO)4. (1)

(c) (i) The rate equation:rate = k[CH3Br][OH-] (1)8.13x10-5 = k (0.2)(0.05) k = 8.13 x 10-3 mol-1dm3s-1 (2)

(ii) ln 8.13 x 10-3 = ln A – Ea/(8.31 x 333.16) ----- (*)ln 50.0 x 10-3 = ln A – Ea/(8.31 x 353.16) ---- (**) (1)(**)-(*)Ea = 88.8 kJ mol-1 (1)

Section B5. (a) (i) CH3CH=CH2 CH3CHBrCH3

HBr(l) at room temperature (1)Electrophilic addition reaction (1)

(ii) CH3CH2CH3 CH3CHBrCH3

Br2(g), UV light (1)Free radical substitution (1)

(iii) CH3CHBrCH3 CH3CH(OH)CH3

Aqueous NaOH, reflux (1)Nucleophilic substitution (1)

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(iv) CH3COCH3 CH3CH(OH)CH3

LiAlH4 (anhydrous) in ether, room temperature. (1)Reduction of ketone to alcohol. (1)

(b) (i) (1) Covalent (1)(2) Tetrahedral (1)

(ii) Pb and butane (1)

(iii) Pb(C2H5)4 + 14O2 PbO2 + 8CO2 + 10H2O (1)

(iv) (1) PbO2(s) (1)

(2) PbBr2 (1)

(3) PbBr2 is volatile and discharged into atmosphere.— Poison catalyst in catalytic converter— Lead is toxic and cause anaemia and brain damage (1)

(iv) Mass Pb = 1 1012 = 3.85 1011 g (1)

= 3.85 108 kg

(c) (i)

and

Warm with aq. NaOH and I2. Cooling of Pentan-2-one (not pentan-3-one) gives yellow crystals of CHI3. (2)

(ii)

Add aq. Bromine.4-methylphenylamine decolorises Br2 and forms a white ppt but not the other compound. (2)

6.(a) (i) Ethanol• Strong hydrogen bonding are formed due to highly polar O—H group

boiling point is higher than simple molecular compounds with similar number of electrons. (1)

• Soluble in water (forms hydrogen bonds with water), soluble in organic solvents (forms dipole-induced dipole). (1)

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(ii) Cis and trans-butenedioic acids• Cis-isomer has overall dipole moment, trans-isomer has zero dipole moment

cis-isomer is polar and trans-isomer is non-polar cis-isomer has higher boiling point than trans. (1)

• Cis-isomer binds together with hydrogen bonds as well as Van der Waal’s forces and thus has a high boiling point. (1)

• Cis-isomer is more soluble in water than trans-isomer and both are expected to be soluble in organic solvents.

(iii) Ethane• Non polar molecules bind together with weak temporary dipole-induced

dipole forces low boiling point. (1)• Insoluble in water (forms only weak dipole-induced dipoles with water) but

soluble in organic liquids. (1)

(b) (i) Concentrated H2SO4 (1)

(ii)(1)

(P)

(1) (2)

trans cis(2)

(3) Two different groups/atoms bonded to each sp2 carbon restricted the rotation about C=C. (1)

(iii) Alcoholic KCN – reflux — step 2 (1)aq. HCl, reflux — step 3 (1)Ethanol, conc. H2SO4 catalyst, reflux — step 4 (1)

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(iv)(1) HBr H+ + Br+

(2) (2)

(2)(v) S would not be chiral as a racemic mixture containing equimolar amounts

of d and l forms of S would be formed. The addition of HBr to a planar carbon can occur from opposite sides. (2)

7 (a) (i) (1) Ether, alkene, ester (1)

(2) Add aq. Br2 at room temperature in the dark. (1)Decolorisation of Br2 occurs. (1)

(1)

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(ii)(1)

(1)

(2)

(1)

(3)

(1)

(iii)

cis trans (2)

Geometric isomerism (1)

(iv) Depletion in ozone layer by reaction with free radicals (formed from CFCs released into the upper atmosphere) occurs. (1)

(b) (i) 6 (1)

(ii)

(1)

(1)

(1)

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(2)

(1)

(iii) Add universal indicator. (1)Aq. B has the highest pH, turns indicator blue.Aq. D has the lowest pH, turns indicator red.Aq. C has a pH between that of B and D. (1)

(c)

(3)

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