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1 BEngTuks.blogspot.com UNIVERSITY O PRETORIA UNIVERSITEIT VAN PRETORIA ` DEPARTEMENT O CHEMISTRY DEPARTMENT CHEMIE Outeursreg voorbehou DATE / DATUM: TIME / TYD: 120 (+20min) MARKS / PUNTE: 80 akulteit Natuur- en Landbouwetenskappe CHM 171 EXAMINATION / EKSAMEN Internal Examiners / Interne Eksaminatore: Dr D Nkosi Dr EMM Venter Dr R Vogel External Examiners / Eksterne Eksaminatore: Mnr N de Bruyn Surname and Initials Van en Voorletters Student number Studentenommer Signature Handtekening Marks / Punte Question 1 / Vraag 1 8 Examiner / Eksaminator Section A Afdeling A Question 2 / Vraag 2 7 Question 3 / Vraag 3 5 Question 4 / Vraag 4 11 Question 5 / Vraag 5 11 [42] Section B Afdeling B [38] 80 SHOW ALL CALCULATIONS / TOON ALLE BEREKENINGE 1) All cell phones must be switched off. / Alle selfone moet afgeskakel wees. 2) Viewing of exam papers, see Click-UP: EXAM INO: 10h00-11h00, Monday 12 th July, lab 1-24, Chemistry Building. / Insae in eksamenvraestel, sien Click-UP EXAM INO : 10h00-11h00, Monday 12de Julie, lab 1-24, Chemie gebou. 1

2 Section A: Show all calculations. / Afdeling A: Toon alle berekeninge. Question 1/ Vraag 1 Question 1a/ Vraag 1a [8] i) Construct a polar molecule using a halogen as central atom with trigonal bipyramidal molecular geometry. Show the three dimensional orientation of all the atoms. (Show both the Lewis dot as well the Lewis line (Couper) structures.) i) Gebruik n halogeen as die sentrale atoom en stel n polêre molekule met trigonale bipiramidale molekulêre geometrie saam. Toon die driedimensionele rangskikking van al die atome. (Toon beide die Lewiskol- asook die Lewislynstrukture.) ii) Indicate the direction of the dipole moment clearly in the three dimensional structure. ii) Toon die rigting van die dipoolmoment duidelik op die driedimensionele struktuur aan. iii) Give all the bond angles in the compound on the Lewis line structure in (i). iii) Gee al die bindingshoeke van die verbinding op die Lewislynstruktuur in (i). Question 1b/ Vraag 1b (6) Complete the following table Voltooi die volgende tabel Cation / Katioon Anion / Anioon ormula / ormule Oxidation number of chlorine/ Oksidasiegetal van chloor Name / Naam Vanadium(IV)perchlorate Vanadium(IV)perchloraat 2

3 Question 2 / Vraag 2. [7] Consider the two reactions A and B. What mass of zinc carbonate will form if you react 1.50 g zinc with 1.50 g sulfur dioxide and reaction A proceeds with a 75.5% yield and reaction B with a 85.0% yield. Beskou die twee reaksies A en B. Watter massa sinkkarbonaat sal vorm indien jy 1.50 g sink reageer met 1.50 g swaeldioksied en reaksie A met n 75.5% en reaksie B met n 85.0% opbrengs verloop? Zn(s) + 2SO 2 (g) ZnS 2 O 4 (s)...a ZnS 2 O 4 (s) + Na 2 CO 3 (aq) ZnCO 3 (s) + Na 2 S 2 O 4 (aq)...b 3

4 Vraag 3/ Question 3 [5] Use the reaction A and thermodynamic data in the table on the data sheet and prove H is a function of state. Gebruik die reaksie A en temodinamiese data in die tabel op die datablad en bewys H is n toestandsfunksie. CH 4 (g) + 2O 2 (g) CO 2 (g) + H 2 O( ) A Question 4/ Vraag 4 [11] a) Consider the following reaction: a) Beskou die volgende reaksie: CS 2 (g) + 3O 2 (g) CO 2 (g) + 2SO 2 (g) Determine whether the reaction is product-favoured or not at 25 C. Bepaal of die reaksie produkbevoordeeld is of nie by 25 C. (6) 4

5 b) The standard free energy change for the reaction b) Die standaard vrye energie verandering vir die reaksie CH 3 CO 2 H(aq) + H 2 O(l) CH 3 CO 2 (aq) + H 3 O + (aq) is kj/mol at 298 K. Decide in which direction the reaction is spontaneous when the concentrations of CH 3 CO 2 H(aq), CH 3 CO 2 (aq), and H 3 O + (aq) are 0.1mol/dm 3, mol/dm 3, and mol/dm 3 respectively. Note: the reaction takes place under non-standard conditions. is kj/mol by 298 K. Besluit in watter rigting die reaksie wel spontaan is wanneer die konsentrasies van CH 3 CO 2 H(aq), CH 3 CO 2 (aq), en H 3 O + (aq) 0.1mol/dm 3, mol/dm 3 en mol/dm 3 respektiwelik is. Let wel: Die reaksie vind onder nie-standaard kondisies plaas. (5) 5

6 Question 5/ Vraag 5 [11] The following redox reaction occurs in a voltaic cell: Die volgende redoksreaksie vind in n voltaïese sel plaas 2Sc(s) + Cr 2 O 7 2- (aq) + 14H + (aq) 2Sc 3+ (aq) + 2Cr 3+ (aq) + 7H 2 O( ) a) The standard cell potential, E cell, for this cell is 3.70 V. Calculate the standard half-cell potential for Scandium a) Die standaard selpotensiaal, E cell, vir hierdie sel is 3.70 V. Bereken die standaard halfselpotensiaal vir Scandium. b) Is the reaction reactant- or product favoured at 25 0 C? Why? b) Is die reaksie reaktant- of produkbevoordeeld by 25 0 C? Hoekom? (1) c) Calculate the cell potential, E cell, when [Cr 2 O 7 2- ] = 6.2 x 10-5 M, [Sc 3+ ] = 0.35 M, [Cr 3+ ] = 0.75 M, and the ph is c) Bereken die selpotensiaal, E cell, indien [Cr 2 O 7 2- ] = 6.2 x 10-5 M, [Sc 3+ ] = 0.35 M, [Cr 3+ ] = 0.75 M en die ph 1.85 is. (4) 6

7 d) What is the effect on the E cell of decreasing the concentration of Cr 2 O 7 2- in the half-cell? d) Wat is die invloed op E cell indien die konsentrasie van Cr 2 O 7 2- verminder in die halfsel? e) What is the effect on the E cell of adding a solution of Mg(NO 3 ) 2 to the anode half cell, increasing the quantity of Mg 2+ but not its concentration? e) Wat is die effek op E cell wanneer n oplossing van Mg(NO 3 ) 2 by die anode halfsel gevoeg word, sodat die Mg 2+ hoeveelheid vermeerder, maar nie die konsentrasie nie. 7

8 Section B: Multiple choice. All and full calculations must be included on this paper to illustrate your answer on the multiple choice paper. Instructions for the multiple choice paper: Answer all the questions on side 2 of the answer sheet provided. Make sure you fill in your name, student number etc in the space provided. Mark only one oval per question. Use a pencil only. Submit both your completed answer sheet and the question paper. Afdeling B: Veelvuldige keuse. Alle en volle berekeninge moet op hierdie antwoordstel ingesluit word, om jou antwoord op die veelvuldige keuse papier te illustreer. Instruksies vir die veelvuldige keuse papier: Beantwoord al die vrae op kant 2 van die antwoordblad. Maak seker dat u u naam, studente nommer ens in die spasie voorsien invul. Merk net een keuse per vraag. Gebruik alleenlik n potlood. Handig beide u voltooide antwoordblad en die vraestel in. Question 1 / Vraag 1 or quality control purposes of the optical reader please colour 1(j), ---in pencil! Kleur asb 1(j) in, vir kwaliteitskontrole van die optiese merkleser,--- met n potlood! Questions 2-6 refer to the following redox reaction. Vrae 2-6 verwys na die volgende redoksreaksie. Balance the following reaction equation, using the half-reaction method in acid. Balanseer die volgende reaksievergelyking deur gebruik te maak van die halfreaksie metode in suur. N 2 H 5 + (aq) + NO 3 (aq) N 2 (g) + NO (g) 8

9 Question 2 / Vraag 2 What is the stoichiometric coefficient of N 2 H 5 + Wat is die stoïgiometriese koëffisiënt van N 2 H 5 + in the final net ionic reaction? in die finale netto ioniese reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 7 h) 8 i) 9 j) none / geeneen Question 3 / Vraag 3 What is the stoichiometric coefficient of NO 3 in the final net ionic reaction? Wat is die stoïgiometriese koëffisiënt van NO 3 in die finale netto ioniese reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 7 h) 8 i) 9 j) none / geeneen Question 4 / Vraag 4 How many electrons are transferred in total in this redox reaction? Hoeveel elektrone word in totaal in hierdie redoksreaksie oorgedra? a) 6 b) 7 c) 8 d) 9 e) 10 f) 11 g) 12 h) 13 i) 14 j) none / geeneen Question 5 / Vraag 5 What is the stoichiometric coefficient of H + in the final net ionic reaction? Wat is die stoïgiometriese koëffisiënt van H + in die finale netto ioniese reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 7 h) 8 i) 9 j) none / geeneen Question 6 / Vraag 6 What is the stoichiometric coefficient of water in the final net ionic reaction? Wat is die stoïgiometriese koëffisiënt van water in die finale netto ioniese reaksie? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 g) 7 h) 8 i) 9 j) none / geeneen Question 7 / Vraag 7 Which period 3 element could have the following ionization energies? (Consider the pattern of relative values carefully.) Watter periode 3 element kan die volgende ionisasie energië besit? (Beskou die patroon van relatiewe waardes versigtig.) IE 1 kj/mol IE 2 kj/mol IE 3 kj/mol IE 4 kj/mol IE 5 kj/mol IE 6 kj/mol (3) 9

10 a) Al b) Si c) P d) S e) C f) none / geeneen Question 8 / Vraag 8 Which period 2 element will have the highest electron affinity? Watter periode 2 element sal die hoogste elektronaffiniteit besit? a) B b) C c) N d) O e) f) Ne g) none / geeneen Question 9 / Vraag 9 An element loses electrons to form a cation with electron configuration [Ar]3d 10. Identify the element and the charge of the cation. n Element X verloor elektrone en vorm die katioon met elektronkonfigurasie [Ar]3d 10. Identifiseer die element en die lading van die katioon. a) Ca 2+ b) K + c) Mg 2+ d) Al 3+ e) Ga 3+ f) In 3+ g) none / geeneen Question 10 / Vraag 10 * 10

11 Consider the given electron distribution for an element. The * identifies a specific electron. What is a possible set of four quantum numbers for this electron, n=, l =, m l =, m s =? Beskou die gegewe elektrondistribusie van n element. Die * identifiseer n spesifieke elektron. Wat is n moontlike stel van vier kwantumgetalle vir hierdie elektron, n=, l =, m l =, m s =? (3) a) 3, 1, 0, + 1 / 2 b) 3, 2, 0, + 1 / 2 c) 5, 2, 1, - 1 / 2 d) 3, 2, 1, - 1 / 2 e) 4, 2, 1, + 1 / 2 f) 4, 1, 0, - 1 / 2 g) none / geeneen Question 11 / Vraag 11 Use the three isotopes of hydrogen protium, deuterium and tritium, 1 H, 2 H and 3 H, and the two isotopes of oxygen, 16 O and 17 O and show how many molecules of water, with different molar mass can possibly form. Gebruik die drie isotope van waterstof protium, deuterium en tritium, 1 H, 2 H en 3 H en die twee isotope van suurstof 16 O en 17 O en toon hoeveel molekules water met verskillende molêre massa kan moontlik vorm. (3) a) 2 b) 3 c) 5 d) 6 e) 9 f) 12 g) 15 h) none / geeneen Question 12 / Vraag mg of an organic compound, containing the elements C, H, N, O and S, represents mol. You determine it also contains 35.4 mg sulphur and 49.4% C, 7.64% H, 17.7% N. Determine the molecular formula of this compound mg van n organiese verbinding bevat die elemente C, H, N, O and S, en verteenwoordig mol. Jy bepaal dit bevat 35.4 mg swael en 49.4% C, 7.64% H, 17.7% N. Bepaal die molekulêre formule van hierdie verbinding. (4) 11

12 a) C 6 H 12 N 2 OS b) C 12 H 22 N 2 O 2 S c) C 13 H 24 N 4 O 3 S d) C 6 H 12 N 2 S e) C 12 H 22 N 2 OS f) C 13 H 24 N 4 O 2 S g) none / geeneen Question 13 / Vraag 13 Which drawing will represent the p z and d x 2 - y 2 orbitals? Watter tekening sal die the p z en d x 2 - y 2 orbitale verteenwoordig? Y Y Y X X X Z Z Z 12

13 a) b) c) Y Y X X None / Geeneen Z d) Z e) f) Question 14 / Vraag 14 Apply the VSEPR model of moleculer geometry and determine which drawing will represent the so-called Lewis dot structure for the ion SO 4 2 Pas die VSEPA- model van molekulêre geometrie toe en bepaal watter tekening sal die sogenaamde Lewiskol-struktuur van die ioon SO 4 2 verteenwoordig. S O 2- S O 2- S O 2- a) b) c) 2- S None / Geeneen O d) e) Question 15 / Vraag 15 Consider the ion SO 4 2 again. The electron pair geometry and molecular geometry will be and. Beskou weereens die verbinding SO 4 2. Die elektronpaargeometrie en die molekulêre geometrie sal en wees. 13

14 a) Octahedral and Octahedral / Oktahedraal en Oktahedraal b) Octahedral and Square Pyramidal / Oktahedraal en Vierkantig Piramidaal. c) Octahedral and Square Planar / Oktahedraal en Vierkantig Planệr d) Trigonal Bipyramidal and Trigonal Bipyramidal / Trigonaal Bipiramidaal en Trigonaal Bipiramidaal. e) Trigonal Bipyramidal and and See-saw / Trigonaal Bipiramidaal en Wipplank. f) Tetrahedral and Tetrahedral / Tetrahedraal en Tetrahedraal g) None / Geeneen Question 16 / Vraag 16 Match the following bond angles (terminal atom, central atom, terminal atom), with PCl 3 Pas die gegewe bindingshoeke (terminale atoom, sentrale atom, terminale atom), met PCl 3. a) Smaller than 180 ( < 180 ) / Kleiner as 180 ( < 180 ) b) 180 c) < 120 d) 120 e) <109.5 f) g) < 90 h) 90 i) none / geeneen Question 17 / Vraag 17 You are interested in the electrolysis of water to form hydrogen and oxygen. You have a choice of 4 batteries to use in the experiment. Which battery(ies) can be used? Jy stel belang in die elektrolise van water om waterstof en suurstof te vorm. Jy moet tussen 4 batterye kies vir die gebruik in die eksperiment. Watter battery(e) kan gebruik word? (3) a) 1.0 V b) 1.20 V c) 1.50 V d) 2.30 V e) 1.20 V, 1.50 V and 2.30 V can be used / 1.20 V, 1.50 V en 2.30 V kan gebruik word. f) 1.50 V and 2.30 V can be used / 1.50 V en 2.30 V kan gebruik word 14

15 g) none / geneen Selected Thermodynamic Values / Sommige Termodinamiese Waardes Species Spesie H f [kj.mol ] ( K) S [JK -1 mol -1 ] ( K) G f [kjmol 1 ] ( K) Species Spesie H f [kj.mol ] ( K) S [JK -1 mol -1 ] ( K) G f [kjmol 1 ] ( K) N 2 H 4 ( ) Cl 2 (g) H 2 (g) H 2 O ( ) N 2 (g) H 2 O (g) CS 2 (g) TiO 2 (s) CO 2 (g) B (s) CH 4 (g) HCl (g) SO 2 (g) NH 4 Cl (s) O 2 (g) C (s) NO(g) NO 2 (g) Avogadro s number / Avogadro se getal = ; (araday)=96485 Coulomb.mol 1 General Gas Constant / Algemene Gaskonstante: R = Jmol 1 K 1 or/of R = L.atm.mol 1 1 cal = J 0 C = K (1) E = q + w; W max =n E, q =.m. T H rxn = H rxn (prod) - H rxn (react/reakt) ( H rxn = rxn H = r H ) 3) S univ = S sys + S surr (4) S surr = qt 1 = H sys T 1 (5) S sys = S sys (prod) - S sys (react/reakt) (6) G sys = H sys -T S sys ( G sys = sys G = s G ) (7) G = G f (prod) - G f (react/reakt) (8) G = G + RTlnQ (9) E = E - R.T(n. ) 1 lnq (10) E = E (n 1 ).lnq. 15

16 (11) G = n.. E (12) G = RTlnK (13) 1Amp.1sec = 1Coulomb (14) 1Watt.1sec = 1Joule (15) 1Joule = 1Volt.1Coulomb (16) Q = Reaction Quotient, At equilibrium, Q = K., G = 0 and E cell = 0. aa(aq) + bb(aq) c C(aq) + dd(aq) K c = [C] c [D] d / [A] a [B] b aa(g) + bb(g) c C(g) + dd(g) K p = p C c p D d / p A a p B b aa(aq) + bb(aq) c C(g) + dd(aq) K = p c C [D] d / [A] a [B] b 16

17 Standard Reduction Potentials In Aqueous at C* Standaard Reduksie Potensiale in Waterige Oplossing by C* E (V) 2 (g) + 2 e 2 (aq) H 2 O 2 (aq) + 2 H 3 O + (aq) + 2 e 4 H 2 O ( ) PbO 2 (s) + SO 4 2 (aq) + 4 H 3 O + (aq) + 2 e PbSO 4 (s) + 6 H 2 O ( ) MnO 4 (aq) + 8 H 3 O + (aq) + 5 e Mn 2+ (aq) + 12 H 2 O ( ) Au 3+ (aq) + 3 e Au (s) C 2 (g) + 2 e 2 C (aq) Cr 2 O 2-7 (aq) + 14H + (aq) + 6 e 2Cr 3+ (aq) + 7H 2 O ( ) O 2 (g) + 4 H 3 O + (aq) + 4 e 6 H 2 O ( ) Br 2 ( ) + 2 e 2 Br (aq) Ag + (aq) + e Ag (s) Hg 2 2+ (aq) + 2 e 2 Hg ( ) e 3+ (aq) + e e 2+ (aq) O 2 (g) + 2 H 2 O ( ) + 4 e 4 OH (aq) Cu 2+ (aq) + 2 e Cu (s) Sn 4+ (aq) + 2 e Sn 2+ (aq) H + (aq) + 2 e H 2 (g) 0.00 Pb 2+ (aq) + 2 e Pb (s) Sn 2+ (aq) + 2 e Sn (s) Ni 2+ (aq) + 2 e Ni (s) V 3+ (aq) + e V 2+ (aq) PbSO 4 (s) + 2 e Pb (s) + SO 4 2 (aq) Cd 2+ (aq) + 2 e Cd (s) e 2+ (aq) + 2 e e (s) Zn 2+ (aq) + 2 e Zn (s) H 2 O ( ) + 2 e H 2 (g) + 2 OH (aq) [Zn(CN) 4 ] 2- (aq) + 2 e Zn (s) + 4 CN - (aq) Al 3+ (aq) + 3 e Al (s) Mg 2+ (aq) + 2 e Mg (s) Na + (aq) + e Na (s) K + (aq) + e K (s) Li + (aq) + e Li (s)

18 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, Li 6,941 4 Be 9, B 10,811 6 C 12,011 7 N 14, O 15, , Ne 20, Na 22, Mg 24,3050 3B 4B 5B 6B 7B 8B 1B 2B 13 Al 26, Si 28, P 30, S 32, Cl 35, Ar 39, K 39, Ca 40, Sc 44, Ti 47,88 23 V 50, Cr 51, Mn 54, e 55, Co 58, Ni 58, Cu 63, Zn 65,39 31 Ga 69, Ge 72,61 33 As 74, Se 78,96 35 Br 79, Kr 83,80 37 Rb 85, Sr 87,62 39 Y 88, Zr 91, Nb 92, Mo 95,94 43 Tc (98) 44 Ru 101,07 45 Rh 102, Pd 106,42 47 Ag 107, Cd 112, In 114,82 50 Sn 118, Sb 121, Te 127,60 53 I 126, Xe 131,29 55 Cs 132, Ba 137, La* 138, Hf 178,49 73 Ta 180, W 183,85 75 Re 186, Os 190,2 77 Ir 192,22 78 Pt 195,08 79 Au 196, Hg 200,59 81 Tl 204, Pb 207,2 83 Bi 208, Po (209) 85 At (210) 86 Rn (222) 87 r (223) 88 Ra 226, Ac** Rf (261) 105 Ha (262) 106 Sg (263) 107 Ns (262) 108 Hs (265) 109 Mt (266) 110 Discovered Nov Discovered Dec 94 LANTHANIDES* 58 Ce 140, Pr 140, Nd 144,24 61 Pm (145) 62 Sm 150,36 63 Eu 151, Gd 157,25 65 Tb 158, Dy 162,50 67 Ho 164, Er 167,26 69 Tm 168, Yb 173,04 71 Lu 174,967 ACTINIDES** 90 Th 232, Pa 231, U 238, Np 237, Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 m (257) 101 Md (258) 102 No (259) 103 Lr (260) R = J K 1 mol 1 = 9.65 x 10 4 C 18