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Surname Centre Number Candidate Signature
Other Names Candidate Number
For Examiners Use
General Certificate of Education June 2007 Advanced Level Examination CHEMISTRY CHM5 Unit 5 Thermodynamics and Further Inorganic Chemistry Monday 25 June 2007 9.00 am to 11.00 am
For this paper you must have G a calculator.
For Examiners Use Question Mark Question Mark
Time allowed: 2 hours Instructions G Use blue or black ink or ball-point pen. G Fill in the boxes at the top of this page. G Answer all questions in Section A and Section B in the spaces provided. All working must be shown. G Do all rough work in this book. Cross through any work you do not want to be marked. G The Periodic Table/Data Sheet is provided on pages 3 and 4. Detach this perforated sheet at the start of the examination. G Section B questions are provided on a perforated sheet. Detach this sheet at the start of the examination. Information G The maximum mark for this paper is 120. G Mark allocations are shown in brackets. G This paper carries 20 per cent of the total marks for Advanced Level. G You are expected to use a calculator where appropriate. G Your answers to the questions in Section B should be written in continuous prose, where appropriate. You will be assessed on your ability to use an appropriate form and style of writing, to organise relevant information clearly and coherently, and to use specialist vocabulary, where appropriate. Advice G You are advised to spend about 1 hour on Section A and about 1 hour on Section B.
1 2 3 4 5 6 7 8
Total (Column 1) Total (Column 2) TOTAL
Examiners Initials
APW/Jun07/CHM5
CHM5
2 SECTION A Answer all questions in the spaces provided.
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1 Consider the incomplete BornHaber cycle and the table of data below.
Mg2 (g) + 2Cl (g)
+
Mg(s) + Cl2(g)
MgCl2(s) Name of standard enthalpy change Enthalpy of atomisation Enthalpy of atomisation Enthalpy of formation First ionisation enthalpy Electron affinity Enthalpy of lattice formation Substance to which enthalpy change refers chlorine magnesium magnesium chloride magnesium chlorine magnesium chloride Value of enthalpy change / kJ mol1 +121 +150 642 +736 364 2493
(a) Complete the Born-Haber cycle above by writing the appropriate chemical formulae, with state symbols, on the dotted lines. (4 marks) (b) Use the cycle and the values given in the table to calculate the second ionisation enthalpy of magnesium. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (3 marks)APW/Jun07/CHM5
The Periodic Table of the Elements
APW/Jun07/CHM5
I
The atomic numbers and approximate relative atomic masses shown in the table are for use in the examination unless stated otherwise in an individual question.
I
II
III
IV
V
VI
VII4.0
0HeHelium
1.0
H6.9 10.8 12.0 14.0 16.0
Hydrogen
Key19.0
1 6.9
9.0
LiLithium Boron Carbon
Be3 27.0 28.1 5 6 7 31.0
relative atomic mass Li B C NNitrogen
2 20.2
OOxygen
FFluorine
NeNeon
Lithium
Beryllium
3
4
atomic number AlAluminium
8 32.1
9 35.5
10 39.9
23.0
24.3
Na Si52.0 54.9 55.8 58.9 58.7 63.5 65.4 13 69.7 14 72.6
Mg
PPhosphorus
SSulphur
ClChlorine
ArArgon
Sodium
Magnesium
Silicon
11
12
39.1
40.1
45.0
47.9
50.9
15 74.9
16 79.0
17 79.9
18 83.8
KChromium Manganese Iron Cobalt Nickel Copper Zinc
Ca24 95.9 98.9 101.1 102.9 106.4 107.9 112.4 25 26 27 28 29 30 31 114.8
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
GaGallium
GeGermanium
AsArsenic
SeSelenium
BrBromine
KrKrypton
Potassium
Calcium
Scandium
Titanium
Vanadium
3
19
20
21
22
23
32 118.7
33 121.8
34 127.6
35 126.9
36 131.3
85.5
87.6
88.9
91.2
92.9
RbMolybdenum Technetium Ruthenium Rhodium Palladium Silver
Sr42 183.9 186.2 190.2 192.2 195.1 197.0 43 44 45 46 47 48 200.6
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
CdCadmium
InIndium
SnTin
SbAntimony
TeTellurium
IIodine
XeXenon
Rubidium
Strontium
Yttrium
Zirconium
Niobium
37
38
39
40
41
49 204.4
50 207.2
51 209.0
52 210.0
53 210.0
54 222.0
132.9
137.3
138.9
178.5
180.9
CsTungsten Rhenium Osmium Iridium Platinum Gold
Ba74 75 76 77 78 79
La
Hf
Ta
W
Re
Os
Ir
Pt
Au80
HgMercury
TlThallium
PbLead
BiBismuth
PoPolonium
AtAstatine
RnRadon
Caesium
Barium
Lanthanum
Hafnium
Tantalum
55
56
57
223.0
226.0
227
*
72
73
81
82
83
84
85
86
Fr
Ra
Ac
Francium
Radium
Actinium
87 140.9 144.2 144.9 150.4
88
89
152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0
140.1
* 58 7159 231.0 238.0 237.0 60 61 62
Lanthanides PaProtactinium Uranium
Ce
Pr
Nd
Pm
Sm63 239.1
EuEuropium
GdGadolinium
TbTerbium
DyDysprosium
HoHolmium
ErErbium
TmThulium
YbYtterbium
LuLutetium
Cerium
Praseodymium Neodymium Promethium Samarium
58
64 243.1 247.1
65 247.1
66 252.1
67 (252)
68 (257)
69 (258)
70 (259)
71 (260)
232.0
90 103 Actinides91 92 93
Th
U
NpNeptunium
PuPlutonium
AmAmericium
CmCurium
Bk94 95 96 97 98
Cf99
EsBerkelium Californium Einsteinium
FmFermium
MdMendelevium
NoNobelium
LrLawrencium
Thorium
90
100
101
102
103
4
Gas constant R = 8.31 J K1 mol1
Table 1 Proton n.m.r chemical shift data Type of proton RCH3 R2CH2 R3CH RCOCH3 ROCH3 RCOOCH3 ROH /ppm 0.71.2 1.21.4 1.41.6 2.12.6 3.13.9 3.74.1 0.55.0
Table 2 Infra-red absorption data Bond CH CC C C C O Wavenumber/cm1 28503300 7501100 16201680 16801750 10001300 32303550 25003000
CO OH (alcohols) OH (acids)
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5 (c) The standard enthalpies of hydration of the Mg2+ and the Cl ions are 1920 kJ mol1 and 364 kJ mol1, respectively. Use this information and data from the table in part (a) to calculate the enthalpy of solution of magnesium chloride. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (3 marks) (d) The standard enthalpy of solution of ammonium chloride, NH+Cl, is +15 kJ mol1. 4 (i) Explain why ammonium chloride dissolves spontaneously in water even though this process is endothermic. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (2 marks) (ii) A 2.0 g sample of ammonium chloride is dissolved in 50 g of water. Both substances are initially at 20 C. Calculate the temperature change and the final temperature of the solution. Assume that the specific heat capacity of the solution is 4.2 J K1 g1. Temperature change ................................................................................................. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... Final temperature of solution ................................................................................... (5 marks) Turn overAPW/Jun07/CHM5
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17
6 2 Data for the following reaction, which represents the reduction of aluminium oxide by carbon, are shown in the table below. Al2O3(s) + 3C(s) 2Al(s) + 3CO(g) Substance Al2O3(s) C(s) Al(s) CO(g) Hf / kJ mol1 1669 0 0 111 S / J K1 mol1 51 6 28 198
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(a) Calculate the values of H , S and G for the above reaction at 298 K and suggest why this reaction is not feasible at 298 K. H ..................................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. S ...................................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. G ..................................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. Reason why this reaction is not feasible at 298 K ............................................................. ............................................................................................................................................. (8 marks)
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7 (b) Calculate the temperature above which this reaction is feasible. (If you have been unable to calculate values for H and S in part (a) you may assume that they are +906 kJ mol1 and +394 J K1 mol1 respectively. These are not the correct values.) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (2 marks) (c) The reaction between aluminium oxide and carbon to form aluminium and carbon monoxide does not occur to a significant extent until the temperature reaches a value about 1000 K above that of the answer to part (b). Give one reason for this. ............................................................................................................................................. (1 mark) (d) State the method used to reduce aluminium oxide on an industrial scale. Give the essential conditions for this industrial process. Method ............................................................................................................................... Conditions .......................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. (3 marks)
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14
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8 3 The table below shows some standard electrode potentials. E /V Fe3+(aq) + e Fe2+(aq) Cr3+(aq) + e Cr2+(aq) Fe2+(aq) + 2e Fe(s) Zn2+(aq) + 2e Zn(s) Cr2+(aq) + 2e Cr(s) + 0.77 0.41 0.44 0.76 0.91
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(a) Predict the products, if any, when the following substances are mixed. In each case use E values from the table to explain your answer. (i) iron metal with aqueous zinc(II) ions Products, if any ......................................................................................................... Explanation .............................................................................................................. ................................................................................................................................... (ii) aqueous iron(III) ions with aqueous chromium(II) ions Products, if any ......................................................................................................... Explanation .............................................................................................................. ................................................................................................................................... (5 marks) (b) Calculate the e.m.f. of the following standard cell and deduce an equation for the overall cell reaction. Zn(s)|Zn2+(aq)||Cr3+(aq),Cr2+(aq)|Pt e.m.f. ................................................................................................................................... Equation ............................................................................................................................. (2 marks)
APW/Jun07/CHM5
9 (c) Chromium(III) ions are weakly acidic in aqueous solution as shown by the following equation. [Cr(H2O)6]3+(aq) [Cr(H2O)5(OH)]2+(aq) + H+(aq)
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The value of Ka for this reaction is 1.15 104 mol dm3. Calculate the pH of a 0.500 mol dm3 solution of [Cr(H2O)6]3+(aq). ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (5 marks) (d) State what you would observe after addition of the following reagents to separate aqueous solutions containing [Cr(H2O)6]3+ ions. In each case give the formula of the chromium-containing product. (i) an excess of NaOH(aq) Observation(s) .......................................................................................................... ................................................................................................................................... Formula of product ................................................................................................... (ii) Na2CO3(aq) Observation(s) .......................................................................................................... ................................................................................................................................... Formula of product ................................................................................................... (5 marks)
17
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10 4 (a) Give the meaning of the term electronegativity. ............................................................................................................................................. ............................................................................................................................................. (2 marks) (b) State and explain the trend in electronegativity across Period 3 from Na to Cl. Trend .................................................................................................................................. Explanation ........................................................................................................................ ............................................................................................................................................. (3 marks) (c) (i) Name the main type of bonding in each of the oxides MgO and P4O10 Bonding in MgO ....................................................................................................... Bonding in P4O10 ..................................................................................................... (ii) Explain how the type of bonding in P4O10 can be predicted by a consideration of electronegativity. ................................................................................................................................... ................................................................................................................................... (3 marks) (d) Write equations for the reaction of Na2O and of SO2 with water. Equation for Na2O ............................................................................................................. Equation for SO2 ................................................................................................................ (2 marks) (e) Write an equation for the reaction of MgO with dilute hydrochloric acid. ............................................................................................................................................. (1 mark) (f) Write an equation for the reaction of P4O10 with an excess of aqueous sodium hydroxide. ............................................................................................................................................. ............................................................................................................................................. (1 mark)
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12APW/Jun07/CHM5
11 SECTION B Detach this perforated sheet. Answer all questions in the spaces provided on pages 13 to 20 of this booklet.
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5
(a) Explain why the ester methyl ethanoate has a lower boiling point than its isomer, propanoic acid. (2 marks) (b) A polyester is formed when ethane-1,2-diol reacts with butanedioic acid. Draw the structure of the repeating unit of this polymer. Suggest why this polyester begins to melt at a higher temperature than poly(ethene) which has molecules of a similar size to those in the polyester. (4 marks) (c) Outline a mechanism for the formation of an ester by the reaction between ethanoyl chloride and an alcohol. (4 marks) (d) The ester ethyl ethanoate is hydrolysed when it is heated with water in the presence of an acid catalyst. An equilibrium is established. CH3COOCH2CH3(l) + H2O(l) CH3COOH(l) + CH3CH2OH(l)
A 0.50 mol sample of ethyl ethanoate was heated with 4.0 mol of water. At equilibrium, 70 % of the ester was hydrolysed. Calculate a value of Kc for this reaction. (5 marks)
6 One characteristic property of transition metals is variable oxidation state. (a) For each of the following processes, write two equations to show how the transition metal catalyst reacts and is reformed. Identify the different oxidation states shown by the transition metal catalyst in each process. (i) the Contact Process catalysed by vanadium(V) oxide (ii) the oxidation of ethanedioate ions by acidified potassium manganate(VII), autocatalysed by Mn2+(aq) ions. (6 marks) (b) Cobalt(II) ions cannot easily be oxidised to cobalt(III) ions in water. Suggest why this oxidation can be carried out in aqueous ammonia and identify a suitable oxidising agent. (3 marks) (c) Metal ions Q2+ in acidified aqueous solution can be oxidised by aqueous potassium dichromate(VI). In a titration, an acidified 25.0 cm3 sample of a 0.140 mol dm3 solution of Q2+(aq) required 29.2 cm3 of a 0.040 mol dm3 solution of potassium dichromate(VI) for complete reaction. Determine the oxidation state of the metal Q after reaction with the potassium dichromate(VI). (6 marks) Turn overAPW/Jun07/CHM5
12 7 The reaction scheme below shows a two-stage synthesis of ethane-1,2-diamine, H2NCH2CH2NH2. Reaction 1 H2C = CH2 BrCH2CH2Br Reaction 2 H2NCH2CH2NH2
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(a) Suggest a reagent for Reaction 1. Name and outline a mechanism for this reaction. (5 marks) (b) Suggest a reagent for Reaction 2. Name the type of mechanism involved and write an equation for the overall reaction. (3 marks) (c) Draw the structure of the complex ion formed when aqueous cobalt(II) ions react with an excess of ethane-1,2-diamine. (2 marks) (d) Ethane-1,2-diamine can be converted into the EDTA4 ion shown below. OOCCH2 NCH2CH2N OOCCH2 CH2COO CH2COO4
State why this ion can act as a multidentate ligand. Write an equation for the reaction of EDTA4 with aqueous cobalt(II) ions. In your equation represent the ligand by EDTA4 Explain why the EDTA4 ion readily displaces unidentate ligands such as water. (5 marks)
8
(a) The compounds CH3CH2Cl and CH3CHCl2 can be distinguished by comparing their proton n.m.r. spectra. For each compound, describe its proton n.m.r. spectrum by giving the number of peaks, the integration ratio and the splitting patterns. (6 marks) (b) The following pairs of compounds can be distinguished using the reagents indicated. Each compound is in a separate aqueous solution. For each one of the compounds, describe what you would observe and write equations for any reactions that occur. (i) KBr and KI using chlorine water (ii) BaCl2 and MgCl2 using dilute sulphuric acid (iii) CoCl2 and CuCl2 using concentrated hydrochloric acid (9 marks)
END OF QUESTIONSAPW/Jun07/CHM5
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APW/Jun07/CHM5