UNIVERSITY OF PRETORIA UNIVERSITEIT VAN PRETORIA ` DEPARTEMENT OF CHEMISTRY DEPARTMENT CHEMIE Outeursreg voorbehou DATE / DATUM: 2008.05.30 TIME / TYD: 120 min MARKS / PUNTE: 80 Fakulteit Natuur- en Landbouwetenskappe CHM 171 EXAMINATION / EKSAMEN Internal Examiners / Interne Eksaminatore: External Examiner / Eksterne Eksaminator: Dr FR Vogel Dr RJ Bowen Dr EMM Venter Prof WJ Schoeman Surname and Initials Van en Voorletters Student number Studentenommer Signature Handtekening Marks / Punte Question 1 / Vraag 1 5 Examiner / Eksaminator Section A Afdeling A Question 2 / Vraag 2 5 Question 3 / Vraag 3 7 Question 4 / Vraag 4 6 Question 5 / Vraag 5 13 Questtion 6 / Vraag 6 9 Section B Afdeling B 38 Total / Totaal 80(+3 bonus) Section A / Afdeling A: Instructions / Instruksies 1. Answer all questions in ink. Answers in pencil will not be marked. Beantwoord alle vrae in ink. Antwoorde in potlood sal nie nagesien word nie. 2. Silent calculators may be used. Geluidlose sakrekenaars mag gebruik word. 3. Do not use Tipp-Ex or any similar liquid paper product on your paper. Answers that should not be marked must be clearly indicated. Geen Tipp-Ex of soortgelyke vloeibare papiermiddels mag op die antwoordstel gebruik word nie. Antwoorde wat nie nagesien moet word nie, moet duidelik doodgetrek word. 4. All cellphones must be switched off. Alle selfone moet afgeskakel wees. 1
Section A / Afdeling A: Show all calculations / Toon alle berekeninge Question 1/ Vraag 1 [5] Fluorocarbonyl hypofluorite has the composition 14.6% C, 39.0% O, and 46.3% F. If the molar mass of the compound is 82 g/mol, determine the molecular formula of the compound. Fluoorkarbonielhipofluoriet bestaan uit 14.6% C, 39.0% O, en 46.3% F. Indien die molekulêre massa van die verbinding 82 g/mol is, bepaal die molekulêre formule van die verbinding. Question 2/ Vraag 2 [5] Silver nitrate is added to a 25 cm 3 sample of hydrochloric acid. A white precipitate of silver chloride is then filtered off. If the dry precipitate weighs 0.3537 g, determine the ph of the hydrochloric acid solution. Silwernitraat word by 25 cm 3 soutsuur oplossing gevoeg. n Wit presipitaat van silwerchloried vorm wat dan afgefiltreer word. Indien die gedroogde presipitaat 0.3537 g weeg, bepaal die ph van die soutsuur oplossing. 2
Vraag 3/ Question 3 [7] Apply Hess s Law, use the data of the given reaction and data from the data table to calculate the enthalpy change for the formation of nitrogen monoxide from its elements. (Hint: Which reaction is described with the data: H f H 2 O(g) = 241.8 kj / mol ) Pas die Wet van Hess toe, gebruik die data van die gegewe reaksie en data uit die datatabel en bereken die entalpie verandering vir die vorming van stikstofmonoksied vanuit sy elemente. (Wenk: Watter reaksie word beskryf met die data: H f H 2 O(g) = 241.8 kj / mol ) 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(g) H rxn = 906.2 kj 3
Vraag 4 / Question 4 [6] How much heat is released when a mixture containing 10.0 g CS 2 and 10.0 g Cl 2 reacts by the equation Hoeveel warmte word afgegee wanneer 10.0 g CS 2 met 10.0 g Cl 2 reageer volgens die vergelyking CS 2 (g) + 3 Cl 2 (g) S 2 Cl 2 (g) + CCl 4 (aq) H = -232 kj 4
Vraag 5 / Question 5 [13] Consider the following reaction: Beskou die volgende reaksie: Ni(s) + 4CO(g) Ni(CO) 4 (g) H f (kj/mol) 0-110.525-602.9 S (J/K mol) 29.87 197.674 410.6 a) Is the reaction product-favoured at 25 C? Is die reaksie produkbevoordeeld by 25 C? [6] b) Is the reaction enthalpy or entropy driven? Explain. Is die reaksie entalpie of entropie gedrewe? Verduidelik. c) What is the value of K at 25 C? Wat is die waarde van K by 25 C? 5
d) At what temperature, in C, will this reaction become spontaneous? By watter temperatuur, in C, sal hierdie reaksie spontaan wees? [3] Question 6 / Vraag 6 [9] Consider the following reaction: Beskou die volgende reaksie: 2MnO 4 (aq) + 5Zn(s) + 16H + (aq) 2Mn 2+ (aq) + 5Zn 2+ (aq) + 8H 2 O(l) a) Determine the cell potential, E cell, at 25 C when the cell is operated at ph 2.00 with [MnO 4 ] = 0.12 mol/dm 3, [Mn 2+ ] = 0.0010 mol/dm 3, and [Zn 2+ ] = 0.015 mol/dm 3. Bepaal die selpotensiaal, E sel, by 25 C van die sel by n ph van 2.00 met [MnO 4 ] = 0.12 mol/dm 3, [Mn 2+ ] = 0.0010 mol/dm 3 en [Zn 2+ ] = 0.015 mol/dm 3. [5] 6
b) Calculate the standard free energy of the cell. Bepaal die standaard vrye energie van die sel. c) Calculate the equilibrium constant for the reaction at 25 C. Bereken die ewewigskonstante vir die reaksie by 25 C. 7
Section B / Afdeling B/: Multiple choice / Veelvuldige keusevrae Instructions: Answer all the questions on side 2 on the answer sheet provided. Complete the biographical section on side 2. Mark only one oval per question. Mark only one oval per question. Use a pencil only. Instruksies: Beantwoord die vrae op die gegewe antwoordblad op kant 2. Voltooi die biografiese inligting op kant 2. Merk net een ovaal per vraag. Gebruik alleenlik n potlood. Question 1 / Vraag 1 For quality control of the optical reader, please colour the oval 1(i). Kleur asseblief die sirkel 1(i), vir die kwaliteitskontrole van die optiese merkleser, in. Question 2 / Vraag 2 [0] When the Fe 3+ cation forms from a neutral Fe atom, the following electrons are lost: Wanneer die Fe 3+ -katioon uit n neutrale Fe-atoom vorm, word die volgende elektrone afgegee: a) one 4s and two 3d electrons / een 4s en twee 3d elektrone b) one 4s, one 3d and one 3p electrons / een 4s, een 3p en een 3s elektrone c) two 4s and one 3d electrons / twee 4s en een 3d elektrone d) one 4s, one 3p and one 3s electrons / een 4s, een 3d en een 3p elektrone e) None of the above / Nie een van bogenoemde nie. Question 3 / Vraag 3 Which of the following orbitals can not exist according to the quantum theory? Watter van die volgende orbitale kan nie volgens die kwantumteorie, bestaan nie? a) 3s b) 3p c) 3d d) 3f e) 4s f) 4p g) 4d h) 4f i) none / geeneen. Question 4 / Vraag 4 Consider the first three elements of the fourth period. Which element will have the largest second ionization energy, IE 2? Beskou die eerste drie elemente van die vierde periode. Watter element sal die grootste tweede ionisasie energie, IE 2, besit? a) Li b) Be c) B d) Na e) Mg f) Al g) K h) Ca i) Sc j) none / geeneen. [3] 8
Question 5 / Vraag 5 Consider the first three elements of the fourth period. Which element will have the largest electron affinity? Beskou die eerste drie elemente van die vierde periode. Watter element sal die grootste elektronaffiniteit besit? a) Li b) Be c) B d) Na e) Mg f) Al g) K h) Ca i) Sc j) none / geeneen. Question 6 / Vraag 6 Consider the densities of the five unknown elements, A E, found in the same period. Which element will be the smallest? Beskou die digthede van die vyf onbekende elemente, A E wat in dieselfde periode voorkom. Watter element sal die kleinste wees? a) A ( ± 0.9 g/cm 3 ) b) B ( ± 1.8 g/cm 3 ) c) C ( ± 3.1 g/cm 3 ) d) D ( ± 4.5 g/cm 3 ) e) E ( ± 6.2 g/cm 3 ) f) none / geeneen. Question 7 / Vraag 7 Consider ClO 2 F + 2. The electron pair geometry and molecular geometry for this ion will be and. Beskou ClO 2 F + 2. Die elektronpaargeometrie en die molekulêre geometrie sal en wees. a) Trigonal Bipyramidal and Trigonal Bipyramidal / Trigonaal Bipiramidaal en Trigonaal Bipiramidaal. b) Trigonal Bipyramidal and and See-saw / Trigonaal Bipiramidaal en Wipplank. c) Octahedral and Square Pyramidal / Oktahedraal en Vierkantig Piramidaal. d) Octahedral and Square Planar / Oktahedraal en Vierkantig Planệr e) Tetrahedral and Tetrahedral / Tetrahedraal en Tetrahedraal f) Tetrahedral and Trigonal Pyramidal / Tetrahedraal en Trigonaal-piramidaal g) None of the above / Nie een van bogenoemde nie. [3] 9
Question 8 / Vraag 8 The approximate sizes of the bonding angles in the following molecule is the following: Die benaderde groottes van die bindingshoeke in die volgende molekule is die volgende: H H N O H a) ±109 & ±120 b) ±109 & ±180 c) ±90 & ±180 d) only / slegs ±120 e) only / slegs ±109 f) None / Geeneen Question 9 / Vraag 9 Which molecule(s) will be polar? Watter molekule(s) is polêr? a) BF 3 b) BF 4 c) CF 3 + d) CF 4 e) BrF 3 f) BrF 4 3+ g) both CF 3 + and BrF 3 / beide CF 3 + en BrF 3 h) both CF 4 and BrF 4 3+ / beide CF 4 en BrF 4 3+ i) none/ geeneen [5] Question 10 / Vraag 10 A hypothetical element consists of two naturally occurring isotopes with the following relative masses: 76.76 amu and 80.94 amu. The percent abundance of the former isotope is 76.31%. The average relative atomic mass of this element is: n Hipotetiese element bestaan uit twee natuurlike isotope met die volgende relatiewe massas: 76.76 ame en 80.94 ame. Die natuurlike voorkoms van die eersgenoemde isotoop is 76.31%. Die gemiddelde relatiewe atoommassa van hierdie element is: a) 120.3 amu b) 78.85 amu c) 77.75 amu d) 60.17 amu e) none / geeneen 10
Question 11 / Vraag 11 [3] Which species below is the nitride ion? Watter van die volgende spesies is die nitriedioon? a) Na + b) NO 3 c) NO 2 e) N 3 f) none / geeneen d) NH 2 [1] Question 12 / Vraag 12 When 175 g water at 24.1 C is mixed with an unknown mass of water at a temperature of 55.1 C, the final temperature of the mixture is 36.6 C. What is the mass of the second sample of water? The specific heat of water is 4.184 J/g K. Indien 175 g water by 24.1 C met n onbekende hoeveelheid water by 55.1 C gemeng word, is die finale temperatuur van die mengsel 36.6 C. Wat is die massa van die tweede monster water? Die spesifieke warmte van water is 4.184 J/g K. a) 32.8 g b) 75.0 g c) 102 g d) 118 g e) 259 g f) none / geeneen [4] 11
Questions 13 to 17 refer to the following unbalanced reaction equation: Vrae 13 tot 17 verwys na die volgende ongebalanseerde reaksie-vergelyking: Cl 2 (g) ClO 3 (aq) + Cl (aq) (in basic solution/ in basiese oplossing) Balance the given reaction equation, using the half-reaction method. Balanseer die gegewe reaksievergelyking, deur gebruik te maak van die halfreaksie-metode. Question 13 / Vraag 13 What is the oxidation number of chlorine in the chlorate ion? Wat is die oksidasiegetal van chloor in die chloraat ioon? a) -6 b) -5 c) -4 d) -2 e) 0 f) +2 g) +4 h) +5 i) +6 j) none / geeneen Question 14 / Vraag 14 [1] How many electrons are transferred in total in this redox reaction? Hoeveel elektrone word in totaal in hierdie redoks-reaksie oorgedra? a) 1 b) 2 c) 3 d) 6 e) 8 f) 10 g) 12 h) none / geeneen 12
Question 15 / Vraag 15 What is the stoichiometric coefficient of Cl 2 in the final reaction? Wat is die stoïgiometriese koëffisiënt van Cl 2 in die finale reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 8 h) 10 i) 12 j) none / geeneen Question 16 / Vraag 16 What is the stoichiometric coefficient of ClO 3 in the final reaction? Wat is die stoïgiometriese koëffisiënt van ClO 3 in die finale reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 8 h) 10 i) 12 j) none / geeneen Question 17 / Vraag 17 What is the stoichiometric coefficient of OH in the final reaction? Wat is die stoïgiometriese koëffisiënt van OH in die finale reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 8 h) 10 i) 12 j) none / geeneen Table / Tabel Species Spesie H f [kj.mol 1 ] (298.15 K) S [JK -1 mol -1 ] (298.15 K) G [kjmol 1 ] (298.15 K) Species Spesie H f [kj.mol 1 ] (298.15 K) S [JK -1 mol -1 ] (298.15 K) G [kjmol 1 ] (298.15 K) C 2 H 6 (g) -83.85 229.2-31.89 Cl 2 (g) 223.08 H 2 (g) 130.7 H 2 O (l) -285.83 69.95-237.15 CH 3 OH (l) -238.4 127.19-166.14 H 2 O (g) -241.8 188.83-228.59 CH 3 OH (g) -201.0 239.7-162.5 Ag + (aq) 77.1 CO 2 (g) -393.5 213.74-393.36 NH 3 (g) 45.9 192.77-16.37 SO 3 (g) -395.77 256.77-371.04 HCl (g) 92.3 64.46-95.3 SO 2 (g) -296.84 248.21-300.13 NH 4 Cl (s) -315.4 42.55-203.9 O 2 (g) 205.07 C (s, graphite / grafiet) 5.6 NaHCO 3 (s) -947.7 102-851.9 Na 2 CO 3 (s) -1130.77 134.79-1048.08 Avogadro s number / Avogadro se getal = 6.0221357 10 23 ; (Faraday)=96485 Coulomb.mol!1 General Gas Constant / Algemene Gaskonstante: R = 8.314510 Jmol!1 K!1 or/of R = 0.082057 L.atm.mol!1 1 cal = 4.184 J 13
0Ε C = 273.15 K (1) E = q + w; W max =n E, q =.m. T (2) HΕ rxn = 3 HΕ rxn (prod) - 3 HΕ rxn (react/reakt) (3) SΕ univ = SΕ sys + SΕ surr (4) SΕ surr = qt!1 =! HΕ sys T!1 (5) SΕ sys = 3 SΕ sys (prod) - 3 SΕ sys (react/reakt) (6) GΕ sys = HΕ sys -T SΕ sys (7) GΕ = 3 GΕ f (prod) - 3 GΕ f (react/reakt) (8) G = GΕ + RTlnQ (9) E = EΕ - R.T(n. )!1 lnq (10) E = EΕ - 0.0257(.n!1 ).lnq. (11) GΕ =!n.. EΕ (12) G = RTlnK (13) 1Amp.1sec = 1Coulomb (14) 1Watt.1sec = 1Joule (15) 1Joule = 1Volt.1Coulomb (16) At equilibrium, E = 0 and Q = K. 14
Standard Reduction Potentials In Aqueous at 25.00ΕC* Standaard Reduksie Potensiale in Waterige Oplossing by 25.00ΕC* EΕ (V) F 2 (g) + 2 eγ 2FΓ (aq) +2.87 H 2 O 2 (aq) + 2 H 3 O + (aq) + 2 eγ 4 H 2 O (Ρ) +1.77 PbO 2 (s) + SO 2 4 Γ (aq) + 4 H 3 O + (aq) + 2 eγ PbSO 4 (s) + 6 H 2 O (Ρ) +1.685 MnO 4 (aq) + 8 H 3 O + (aq) + 5 eγ Mn 2+ (aq) + 12 H 2 O (Ρ) +1.52 Au 3+ (aq) + 3 eγ Au (s) +1.50 O 2 (g) + 4 H 3 O + (aq) + 4 eγ 6 H 2 O (Ρ) +1.229 Br 2 (Ρ) + 2 eγ 2 BrΓ (aq) +1.08 NO 3 (aq) + 4 H 3 O + (aq) + 3 eγ NO (g) + 6 H 2 O (Ρ) +0.96 OClΓ (aq) + H 2 O (Ρ) + 2 eγ ClΓ (aq) + 2 OHΓ (aq) +0.89 Ag + (aq) + eγ Ag (s) +0.80 2+ Hg 2 (aq) + 2 eγ 2 Hg (Ρ) +0.789 Fe 3+ (aq) + eγ Fe 2+ (aq) +0.77 I 2 (s) + 2 eγ 2 IΓ (aq) +0.535 O 2 (g) + 2 H 2 O (Ρ) + 4 eγ 4 OHΓ (aq) +0.40 Cu 2+ (aq) + 2 eγ Cu (s) +0.337 Sn 4+ (aq) + 2 eγ Sn 2+ (aq) +0.15 2 H 3 O + (aq) + 2 eγ H 2 (g) + 2 H 2 O (Ρ) 0.00 Pb 2+ (aq) + 2 eγ Pb (s) -0.125 Sn 2+ (aq) + 2 eγ Sn (s) -0.14 Ni 2+ (aq) + 2 eγ Ni (s) -0.25 V 3+ (aq) + eγ V 2+ (aq) -0.255 PbSO 4 (s) + 2 eγ Pb (s) + SO 2 4 Γ (aq) -0.356 Cd 2+ (aq) + 2 eγ Cd (s) -0.40 Fe 2+ (aq) + 2 eγ Fe (s) -0.44 Zn 2+ (aq) + 2 eγ Zn (s) -0.763 2 H 2 O (Ρ) + 2 eγ H 2 (g) + 2 OHΓ (aq) -0.8277 [Zn(CN) 4 ] 2- (aq) + 2 eγ Zn (s) + 4 CN - (aq) -1.26 Al 3+ (aq) + 3 eγ Al (s) -1.66 Mg 2+ (aq) + 2 eγ Mg (s) -2.37 Na + (aq) + eγ Na (s) -2.714 K + (aq) + eγ K (s) -2.925 Li + (aq) + eγ Li (s) -3.045 15
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Periodic table of the elements / Periodieke tabel van die elemente 1A 1 H 1,0079 2A 3A 4A 5A 6A 7A 8A 2 He 4,0026 3 Li 6,941 4 Be 9,0122 5 B 10,811 6 C 12,011 7 N 14,0067 8 O 15,9994 9 F 18,9984 10 Ne 20,1797 11 Na 22,9898 12 Mg 24,3050 3B 4B 5B 6B 7B 8B 1B 2B 13 Al 26,9815 14 Si 28,0855 15 P 30,9738 16 S 32,066 17 Cl 35,4527 18 Ar 39,948 19 K 39,0983 20 Ca 40,078 21 Sc 44,9559 22 Ti 47,88 23 V 50,9415 24 Cr 51,9961 25 Mn 54,9380 26 Fe 55,847 27 Co 58,9332 28 Ni 58,693 29 Cu 63,546 30 Zn 65,39 31 Ga 69,723 32 Ge 72,61 33 As 74,9216 34 Se 78,96 35 Br 79,904 36 Kr 83,80 37 Rb 85,4678 38 Sr 87,62 39 Y 88,9059 40 Zr 91,224 41 Nb 92,9064 42 Mo 95,94 43 Tc (98) 44 Ru 101,07 45 Rh 102,9055 46 Pd 106,42 47 Ag 107,8682 48 Cd 112,411 49 In 114,82 50 Sn 118,710 51 Sb 121,757 52 Te 127,60 53 I 126,9045 54 Xe 131,29 55 Cs 132,9054 56 Ba 137,327 57 La* 138,9055 72 Hf 178,49 73 Ta 180,9479 74 W 183,85 75 Re 186,207 76 Os 190,2 77 Ir 192,22 78 Pt 195,08 79 Au 196,9665 80 Hg 200,59 81 Tl 204,3833 82 Pb 207,2 83 Bi 208,9804 84 Po (209) 85 At (210) 86 Rn (222) 87 Fr (223) 88 Ra 226,0254 89 Ac** 227.0278 104 Rf (261) 105 Ha (262) 106 Sg (263) 107 Ns (262) 108 Hs (265) 109 Mt (266) 110 Discovered Nov 94 111 Discovered Dec 94 LANTHANIDES* 58 Ce 140,115 59 Pr 140,9076 60 Nd 144,24 61 Pm (145) 62 Sm 150,36 63 Eu 151,965 64 Gd 157,25 65 Tb 158,9253 66 Dy 162,50 67 Ho 164,9303 68 Er 167,26 69 Tm 168,9342 70 Yb 173,04 71 Lu 174,967 ACTINIDES** 90 Th 232,0381 91 Pa 231,0359 92 U 238,0289 93 Np 237,0482 94 Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (260) R = 8.314 J KΓ 1 molγ 1 F = 9.65 x 10 4 C 17