UNIVERSITY OF PRETORIA UNIVERSITEIT VAN PRETORIA DEPARTMENT OF CHEMISTRY DEPARTEMENT CHEMIE DATE / DATUM : 07/11/2007 TIME / TYD : 120 min MARKS / PUNTE : 85 EXAMINERS:/ EKSAMINATORE: External / Ekstern: CHM 181 Dr S Bauermeister Prof S Lotz Dr EMM Venter Prof WJ Schoeman SURNAME AND INITIALS : ------------------------------------------------------------------------------ VAN EN VOORLETTERS REGISTRATION NUMBER: ----------------------------------- DEGREE COURSE:: --------- REGISTRASIENOMMER GRAAD KURSUS SIGNATURE / HANDTEKENING: ----------------------------------------------------------------------- Question Vraag Marks / Punte 1 9 2 17 3 10 4 24 5 25 Examiner Eksaminator Use line (zig-zag) structures for the organic compounds. Show ALL calculations in the Analytic/Physical Section. Data page included. Gebruik lyn ( sig-sag) strukture vir die organiese verbindings. Toon ALLE berekeninge in die Analitiese/Fisiese Afdeling. Inligtingsblad ingesluit. 1
Question 1a / Vraag 1a i. Give the line structure of (2E)-2-(1-chloroethyl)-3-ethyl-2-pentene-1,4-diol. i. Gee die lynstruktuur van (2E)-2-(1-chloroetiel)-3-etiel-2-penteen-1,4-diol. (4) Question 1b / Vraag 1b i. Draw the most stable conformer of (1R, 3S)-3-chloro-1-isopropylchlorocyclohexane. Start with carbon one on the indicated dot and complete the drawing to the right. i. Teken die stabielste konformeer van (1R, 3S)-3-chloro-1-isopropielsikloheksaan. Begin met koolstofatoom een op die gegewe kol en voltooi die tekening na regs. (5) C-1 2
Question 2a. / Vraag 2a. (R)-3-Bromocyclohexene reacts with Br 2 to give two stereoisomers, compounds A and B. (R)-3-Bromosiklohekseen reageer met Br 2 om twee stereoisomere, verbindings A en B, te lewer. Br 2 A + B Br i. Use your knowledge of the stereochemistry of the addition of Br 2 to a double bond and of stereochemical principles to assign structures to A and B. i. Gebruik jou kennis van die stereochemie van Br 2 addisie aan n dubbelbinding en van stereochemiese beginsels om strukture aan verbindings A en B toe te ken. (4) ii. Redraw compound A, number all the carbon atoms and give the absolute configuration of each stereogenic sentrum. ii. Herteken verbinding A, nommer al die koolstofatome en gee die absolute konfigurasie van elke stereogeniese sentrum. (2) iii. What is the stereochemical relationship between the two products, A and B? iii. Wat is die stereochemiese verwantskap tussen die twee verbindings, A en B? (1) 3
iv. Are the two products chiral? Give reasons for your answer. iv. Is die twee produkte chiraal? Gee redes vir jou antwoord. (2) v. Show, by using curved arrows how the bromonium ion, that will eventually lead to the outcome of the reaction, will form as first step in the mechanism. Do not give the complete reaction mechanism v. Toon, deur gebruik te maak van geboë pyle, hoe die bromoniumioon, wat uiteindelik sal lei tot die uitkoms van die reaksie, in die eerste stap van die meganisme vorm. Moet nie die volle meganisme gee nie. (4) Question 2b. / Vraag 2b. Explain why the hydration of 1-methylcyclohexene gives 1-methyl-1-cyclohexanol as the only product. Use line structures and arrows to represent the movement of electrons and illustrate the formation of an intermediate or intermediates. A complete mechanism is not required. Verduidelik waarom die hidrasie van 1-metielsiklohekseen slegs 1-metiel-1-sikloheksanol as produk lewer. Gebruik lynstrukture en pyle om die beweging van elektrone aan te dui, om die vorming van n tussenproduk of tussenprodukte te illustreer. n Volledige meganisme word nie vereis nie. (4) 4
Question 3a. / Vraag 3a. Show how you would accomplish the following transformation. You may use any additional reagents you need. Toon aan hoe jy die volgende omskakeling sal bewerkstellig. Jy mag enige addisionele reagense wat benodig word gebruik. (6) Br O 5
Question 3c. / Vraag 3c. Show how you would synthesize the reagent, t-butoxide [(CH 3 ) 3 CO ] starting from a hydrocarbon substrate. You may use any additional reagents you need. Toon aan hoe jy die reagenst t-butoksied [(CH 3 ) 3 CO ] sal sintetiseer, deur gebruik te maak van n koolwaterstofverbinding as die uitgangstof. Jy mag enige addisionele reagense wat benodig word gebruik. (4) 6
Question 4a / Vraag 4a i. How many grams of which salt must be added to 500. cm 3 0.125 M benzoic acid, C 6 H 5 COOH, solution to render a buffer with ph 4.55? Give the reaction equations of the equilibrium that must be considered and ICE table. Assume there will be no change in volume. i. Hoeveel gram van watter sout moet by 500. cm 3 0.125 M bensoësuur, C 6 H 5 COOH, oplossing gevoeg word om n buffer met ph 4.55 te gee. Gee die reaksie-vergelykings van die ewewig wat in aggeneem moet word en die ICE tabel. Neem aan dat daar geen verandering in volume sal wees nie. (8) 7
Question 4b / Vraag 4b Nicotine, C 10 H 14 N 2, is a diprotic weak base. Give the reaction equations to illustrate the ionization of nicotine in water and calculate the ph of a 0.020 M solution. Nikotien, C 10 H 14 N 2, is n diprotiese swak basis. Gee die reaksievergelykings om die ionisasie van nikotien in water te illustreer en bereken die ph van n 0.020 M oplossing. K b1 = 7.0 10 7 K b2 = 1.1 10!10 (8) 8
Question 4c / Vraag 4c i. Calculate the K sp of Ag 2 CrO 4, if the solubility of the salt in pure water is 1.3x10 4 mol.dm 3. i. Bereken die K sp van Ag 2 CrO 4, indien die oplosbaarheid van die sout in suiwer water 1.3x10 4 mol.dm 3 is. (4) 9
ii. What will the solubility of the salt be in a 0.050 M silver nitrate solution. ii. Wat sal die oplosbaarheid van die sout in n 0.050 M silwernitraat oplossing wees? (4) 10
Question 5a Vraag 5a A 10.0 L flask contains 3.2 g of methane, 0.6 g of hydrogen and 11.2 g nitrogen at 25 C. What is the pressure in atmospheres inside the closed flask? n 10.0 L fles bevat 3.2 g metaan, 0.6 g waterstof en 11.2 g stikstof by 25 C. Wat is die druk in atmosfeer aan die binnekant van die geslote fles? (6) Question 5b/Vraag 5b Within the group of molecules identify the intermolecular forces operative and on the basis of these, assign the boiling points to appropriate molecules. / Identifiseer die intermolekulere kragte wat n rol speel by elkeen van die verbindings hieronder en ken kookpunte toe aan elkeen op grond hiervan. Molecules / Molekule: H 2, CH 3 OCH 3, C 2 H 6 and / en CH 3 OH Boiling points / Kookpunte ( C): 65, -25, -89, -253 (8) 11
Question 5c/Vraag 5c i. We dissolve 300 mg of the tripeptide glutathione in 10.0 g of water. If the osmotic pressure of the solution at 25 C is 2.41 atm, (i.a) calculate the molecular mass of glutathione, (i.b) calculate the freezing point of the solution. i. 300 mg van die tripeptied glutatioon word opgelos in 10.0 g water. As die osmotiese druk van die oplossing by 25 C, 2.41 atm is, (i.a) bereken die molekulêre massa van glutatioon, (i.b) bereken die vriespunt van die oplossing. (5) 12
ii. Suppose we are trying to use freezing point measurements to determine the molecular weight of glutathione and we make an error of 0.01 C (reasonable) in the temperature measurement. What percentage error would this cause in the calculated molecular weight? ii. Indien ons probeer om vriespuntmetings te gebruik om die molekulere massa van glutatioon te bereken en ons maak n fout van 0.01 C (redelik)in die temperatuurmeting. Watter persentasie fout sal dit verteenwoordig in die berekende molekulêre massa? (2) 13
iii. Suppose we can measure the osmotic pressure with an error of only 0.1 torr (reasonable, 1 atm = 760 torr). What percentage error would this cause in the calculated molecular weight? iii. Indien ons die osmotiese druk met n fout van slegs 0.1 torr kan meet (redelik, 1 atm = 760 torr). Watter persentasie fout sal dit veroorsaak in die berekening van die molekulêre massa van glutatioon? (2) iv. Make a conclusion from your answer in (ii) and (iii) about the better method to determine molecular weights. (Assume the density of water is 1.00 g/cm 3 ; freezing point (H 2 O) = 0.0 C; K f (H 2 O) = 1.86 C/m). iv. Maak n afleiding uit jou antwoorde in (ii) en (iii) oor die beter metode om molekulere massa te bereken.(aanvaar die digtheid van water as 1.00 g/cm 3 ; die vriespunt van water 0.0 C; K f (H 2 O) = 1.86 C/m) (2) 14
Ionization Constants for Some Acids / Ionisasie Konstantes vir Sekere Sure K a H 2 SO 3 1.2 10!2! HSO 4 1.2 10!2 H 3 PO 4 7.5 10!3 HF 7.2 10!4 HNO 2 4.5 10!4 C 6 H 5 COOH 6.3 10 5 CH 3 COOH 1.8 10!5 H 2 CO 3 4.2 10!7 H 2 S 1. 10!7! H 2 PO 4 6.2 10!8! HSO 3 6.2 10!8 HOCl 3.5 10!8 + NH 4 5.6 10!10 HCN 4.0 10!10! HCO 3 4.8 10!11 2! HPO 4 3.6 10!13 H 2 O 1.8 10!16 HS! 1. 10!19 Solubility Product for selected salts / Oplosbaarheidsproduk vir selektiewe soute. K sp PbSO 4 PbCO 3 Pb(OH) 2 PbF 2 PbCl 2 PbBr 2 PbI 2 2.5x10 8 7.4x10 14 1.4x10 15 3.3x10 8 1.7x10 5 6.6x10 6 9.8x10 9 Some Formulae / n Paar Formules K a K b = K w ; K w = [H 3 O + ][OH ] = 1.01 x 10 14 at 25 C ph = pk a + log {[conjugate base] / [acid]} Avogadro s number / Avogadro se getal : 6.02214199 10 23 Gas constant: / Gaskonstante: R: 0.082057 L.atm.mol!1.K!1 ; 8.314510 J.mol!1.K!1 1 atm = 760 mmhg = 760 torr. 15
Gas Equations:/ Gasvergelykings: P tot =P 1 + P 2 + P 3 +...; P tot =n tot (RT/V); P a =P a (P tot ); (P + a[n/v] 2 )(V-bn)=nRT Solvent and Solute Laws: / Oplosmiddel en Opgeloste Stof Wette: bp = bpt = boiling point / kookpunt. fp = fpt = freezing point / vriespunt. Sg=k H P g ; P solv =P solv PE solv ; )P solv =!P solute PE solv ; )T bp = K bp m solute ; )T fp = K fp m solute ; )T fp (measured) = K fp m solute i Osmotic pressure / Osmotiese druk: A= crt Water: K fp =!1.86 EC / m K bp = + 0.5121 EC / m 16
Periodic table of the elements / Periodieke tabel van die elemente 1A 8A 1 H 1,0079 2A 3A 4A 5A 6A 7A 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@KG 1 molg 1 F = 9.65 x 10 4 C 17