DEPARTEMENT CHEMIE DEPARTMENT OF CHEMISTRY CMY 127 FINALE EKSAMEN / FINAL EXAMINATION AFDELING A / SECTION A DATUM / DATE: 12 November 2009 EKSAMINATORE / Mrs. AC Botha TYD / TIME: 2 ½ uur / hours EXAMINERS: Dr. BJ Laurens PUNTE / MARKS: 100 Prof. WJ Schoeman Dr. L Pilcher Dr. M Potgieter Dr. MM Nkwelo EKSTERNE / Prof. R Vleggaar EXTERNAL: Dr. L vd Merwe Van en Voorletters: Surname and Initials: Studentenommer: Student Number: Handtekening: Signature: ************************************ VRAAG/ QUESTION PUNTE / MARKS EKSAMINATOR /EXAMINER 1 14 2 14 3 9 4 9 5 8 6 17 TOTAAL: AFDELING B TOTAL: SECTION B 33 TOTAAL / TOTAL 100 INSTRUKSIES 1. 'n Datablad is aangeheg aan Afdeling B. 2. Alle antwoorde (berekeninge, diagramme, Lewisstrukture) moet in ink gegee word. Antwoorde in potlood word nie aanvaar nie. 3. Alle berekeninge moet volledig getoon word. Alle stappe moet gegee word. 4. Die korrekte aantal betekenisvolle syfers moet deurgaans in alle berekeninge gegee word. INSTRUCTIONS 1. An information sheet is attached to Section B. 2. All answers (calculations, diagrams, Lewis structures) must be given in ink. Answers in pencil will not be accepted. 3. All calculations must be shown in full. All steps must be given. 4. The correct number of significant figures must be given throughout in all calculations. Page 1 of 10
Vraag 1 Oplossings en Termochemie [14] Question 1 Solutions and Thermochemistry [14] 1.1 2.56 g Swael word verbrand in n bom kalorimeter in die teenwoordigheid van oormaat O 2 (g). Die temperatuur verhoog van 21.25 o C na 26.72 o C. Die bom het n warmtekapasiteit van 923 J/K. en die kalorimeter bevat 815 g water. Bereken die warmte wat gegenereer word, per mol SO 2 wat gevorm word in die reaksie: S 8 (s) + 8 O 2 (g) 8 SO 2 (g) [5] 1.1 2.56 g Sulphur is burned in a bomb calorimeter with excess O 2 (g). The temperature increases from 21.25 o C to 26.72 o C. The bomb has a heat capacity of 923 J/K. and the calorimeter contains 815 g of water. Calculate the heat evolved, per mole of SO 2 formed, for the reaction: S 8 (s) + 8 O 2 (g) 8 SO 2 (g) [5] Page 2 of 10
1.2 Gebutuleerde hidroksie-anisool (BHA) word gebruik as n anti oksidant in margarine en ander vette en olies; dit verhoed oksidasie en verleng die rakleeftyd van voedsel. Bereken die molêre massa van BHA indien 0.640 g van die verbinding, opgelos in 25.0 g chloroform, n oplossing lewer met n kookpunt van 62.22 o C? [K bp vir CHCl 3 = 3.63 o C/m; T bp vir CHCl 3 = 61.70 o C] [4] 1.2 Butylated hydroxyanisole (BHA) is used as an antioxidant in margarine and other fats and oils; it prevents oxidation and prolongs the shelf life of food. What is the molar mass of BHA if 0.640 g of the compound, dissolved in 25.0 g of chloroform, produces a solution whose boiling point is 62.22 o C? [K bp for CHCl 3 = 3.63 o C/m; T bp for CHCl 3 = 61.70 o C] [4] 1.3 Suiwer etileenglikol [HOCH 2 CH 2 OH] word by 2 kg water in die verkoel sisteem van n motor gevoeg. Die dampdruk van die water in die sisteem, by n temperatuur van is 90 o C, is 457mmHg. Bereken die massa etileenglikol wat bygevoeg is. [Dampdruk van water by 90 o C = 525.8 mmhg] [5] 1.3 Pure ethylene glycol [HOCH 2 CH 2 OH] is added to 2 kg of water in the cooling system of a car. The vapour pressure of the water in the system when the temperature is 90 o C is 457mmHg. What mass of ethylene glycol was added? [Vapour pressure of water at 90 o C = 525.8 mmhg] [5] Page 3 of 10
Vraag 2 Termodinamika en Elektrochemie [14] Question 2 Thermodynamics and Electrochemistry [14] 2.1 Die onderstaande figuur toon die verwantskap tussen G en die natuurlike logaritme van die reaksiekwosiënt van die vorming van ammoniak vanuit sy elemente by 25 C: 2.1 The figure below shows the relationship between G and the natural logarithm of the reaction quotient for the formation of ammonia from its elements at 25 C: N 2 (g) + 3H 2 (g) 2NH 3 (g) Hº = 46 kj/mol G (kj/mol) 40 20 0-30 -20-10 0 10 20 30 ln Q p -20-40 -60-80 -100 2.1.1 Merk die punt op die reguit lyn met n kruisie ( ) waar die sisteem in ewewig is. [1] 2.1.1 Mark the point on the straight line at which the system is at equilibrium with a cross ( ). [1] 2.1.2 Merk die punt op die reguit lyn met n diamantsimbool ( ) waar G gelyk is aan die standaard vrye 2.1.2 Mark the point on the straight line at which G is equal to the standard free energy change of reaction energie-verandering van die reaksie. [1] with a diamond symbol ( ). [1] 2.1.3 Is hierdie reaksie spontaan by 25 C? Motiveer u antwoord. [2] 2.1.3 Is this reaction spontaneous at 25ºC? Motivate your answer. [2] Page 4 of 10
2.1.4 Bereken die ewewigkonstante van hierdie reaksie by 25 C. [1] 2.1.4 Calculate the equilibrium constant of this reaction at 25 C. [1] 2.1.5 Bereken die standaard entropieverandering van hierdie reaksie by 25 C. [3] 2.1.5 Calculate the standard entropy change for this reaction at 25ºC. [3] Page 5 of 10
2.2 Voorspel of goudmetaal by 25 C deur 1 M salpetersuur opgelos kan word om n 1 M Au 3+ (aq) oplossing te vorm. Skryf die oksidasie- en reduksie-halfreaksies en voorsien berekeninge om u antwoord te staaf. [6] 2.2 Predict whether 1 M nitric acid will dissolve gold metal at 25 C to form a 1 M Au 3+ (aq) solution. Write the oxidation and reduction half-reactions and show the calculations that support your answer. [6] Page 6 of 10
Vraag 3 / Question 3: Benaming, / Nomenclature, [9] 3.1 Benaam die volgende verbindings volgens IUPAC-reëls. Name the following compounds according to IUPAC rules. OH Naam:.. (2) Name: O O Naam:.. (2) Name: 3.2 Teken n duidelike lynstruktuur van oksaalsuur. Draw a clear line structure for oxalic acid. (1) 3.3 Teken n lynstruktuur met duidelike uitbeelding van die stereochemie van (2S,3Z)-2-chloro-3- feniel-3-pentenaal. Plaas C-1 aan die regterkant van die struktuur. Draw a line structure clearly showing the stereochemistry of (2S,3Z)-2-chloro-3-phenyl-3- pentenal. Place C-1 on the right-hand side of the line structure. (4) Vraag 4 / Question 4 : Meganismes / Mechanisms [9] 4.1 Bestudeer die geboë pyle in die reaksie hieronder Study the curved arrows in the reaction below: 4.1.1 Verskaf n lynstruktuur van die produk wat in die reaksie gevorm word. Provide a line structure of the product that forms in the reaction. (2) 4.1.2 Watter uitgangstof is die elektrofiel? Which substrate is the electrophile?.. (1) Page 7 of 10
4.2 Stel n meganisme voor vir die reaksie van waterstofbromiedgas met 2-metiel-2-buteen. Toon die struktuur van die tussenprodukte en gebruik geboë pyle om elektronbeweging in elke stap aan te dui. Toon slegs hoe die hoofproduk gevorm word. Propose a mechanism for the reaction of hydrogen bromide gas with 2-methyl-2-butene showing the structures of the intermediates and using curved arrows to indicate electron flow in each step. Only show the formation of the major product. (6) Vraag 5 / Question 5: Koolhidrate / Carbohydrates [8] 5.1 Voltooi die volgende reaksieskema. / Complete the following reaction scheme. (4) 5.2 Verskaf n naam vir die monosakkaried M. / Provide a name for the monosaccharide M. (1) Naam / Name:.. 5.3.1 Gebruik een van die template om die mees stabiele konformasie van N te teken. / Draw the most stable conformation of N using one of the templates provided. (2) 5.3.2 Identifiseer die anomeriese koolstof in jou stoelstruktuur. / Identify the anomeric carbon in your chair structure. (1) Page 8 of 10
Vraag 6 / Question 6: Organiese Reaksies / Organic Reactions [17] 6.1 Verskaf die ontbrekende reagense en die lynstrukture van die uitgangstowwe en produkte in die volgende reaksies. Geen stereochemie word vereis nie. Provide the missing reagents and line structures of substrates and products for the following reactions. No stereochemistry is required. Page 9 of 10
6.2 Skryf reaksievergelykings vir die sintetiese omskakeling van 2-metielpropanaal na isobutielchloried. Elke reaksiestap moet deur n volledige vergelyking voorgestel word waarin uitgangstof, reagense en organiese produkte aangetoon word. Meganismes word nie vereis nie. Write reaction equations for the synthetic conversion fo 2-methylpropanal to isobutyl chloride. Each reaction step must be fully presented, including substrate, reagents and organic products. Mechanisms are not required. (4) (13) Page 10 of 10