DEPARTEMENT CHEMIE DEPARTMENT OF CHEMISTRY CMY 127 EKSAMEN / EXAMINATION DATUM / DATE: 20 November 2012 EKSAMINATORE: Prof. WJ Schoeman EXAMINERS: Prof. M Potgieter TYD / TIME: 3 ure / hours Prof. R Vleggaar PUNTE / MARKS: 100 Ms BA Castleman Afdeling A / Section A: 66 Dr P Coleman Afdeling B / Section B: 36 EKSTERN / EXTERNAL: Dr LA Pilcher Mr N de Beer ************************************ AFDELING A / SECTION A VAN EN VOORLETTERS: ----------------------------------------------------------------------------- SURNAME AND INITIALS: REGISTRASIENOMMER: ---------------------------- GRAADKURSUS: ------------------------ REGISTRATION NUMBER: DEGREE COURSE: HANDTEKENING / SIGNATURE : ----------------------------------------------------- VRAAG QUESTION PUNTE MARKS 1 11 EKSAMINATOR EXAMINER 2 13 3 8 4 18 5 16 TOTAAL:AFDELING A TOTAL:SECTION A TOTAAL:AFDELING B TOTAL:SECTION B 66 36 TOTAAL / TOTAL 100 INSTRUKSIES Alle berekeninge, sketse en diagramme moet in ink gegee word. Alle berekeninge moet volledig getoon word. Antwoorde moet tot die korrekte aantal betekenisvolle syfers gegee word. n Inligtingsblad is aangeheg aan Afdeling B. INSTRUCTIONS All answers (calculations, sketches, and diagrams) must be given in ink. All calculations must be shown in full. Answers must be given to the correct number of significant figures. An information page is attached to Section B.
Vraag 1 Elektrochemie [11] n Onbekende metaal M vorm n oplosbare verbinding M(NO 3 ) 2. n Oplossing van M(NO 3 ) 2 word ge-elektroliseer. Wanneer n konstante elektriese stroom van 2.50 ampère deurvloei vir 35.0 minute, word 3.06 g van metaal M geplateer. 1.1 Bereken die molêre massa van M en identifiseer die metaal. [3] Question 1 Electrochemistry [11] An unknown metal M forms a soluble compound, M(NO 3 ) 2. A solution of M(NO 3 ) 2 is electrolyzed. When a constant current of 2.50 amperes is applied for 35.0 minutes, 3.06 grams of the metal M is deposited. 1.1 Calculate the molar mass of M and identify the metal. [3] 1.2 Die metaal wat hierbo geïdentifiseer is, word met sinkmetaal gebruik om n galvaniese sel te maak, soos hieronder aangedui. 1.2 The metal identified above is used with zinc metal to construct a galvanic cell, as shown below. Skryf die netto ioniese vergelyking van die selreaksie en bereken die selpotensiaal, E. [3] Write the net ionic equation for the cell reaction and calculate the cell potential, E. [3] CMY 127 Examination / Eksamen 2/10 2012
1.3 Bereken die waarde van die standaard vrye energieverandering, G, by 25 C vir die reaksie in die sel hierbo. [2] 1.3 Calculate the value of the standard free energy change, G, at 25 C for the reaction in the cell above. [2] 1.4 Bereken die potensiaal E vir die sel hierbo wanneer die beginkonsentrasie van Zn(NO 3 ) 2 0.10 M is, maar die konsentrasie van M(NO 3 ) 2 bly 1.0 M. [3] 1.4 Calculate the potential, E, for the cell shown above if the initial concentration of ZnSO 4 is 0.10 M, but the concentration of the M(NO 3 ) 2 solution remains 1.0 M. [3] CMY 127 Examination / Eksamen 3/10 2012
Vraag 2 Oplossings en Gasse [13] Question 2 Solutions and Gases [13] 2.1 Die verbinding metieltallium, Tl(CH 3 ) x, bestaan. Om die formule te bepaal, was 0.102 g daarvan gereageer met HCl. Die waterstofatoom van die suur kombineer met CH 3 om metaangas (CH 4 ) te vorm. Die geïsoleerde metaangas het n druk van 90.6 mm Hg en n volume van 256 ml by 30.0 C. Bepaal die formule van metieltallium. [7] 2.1 The compound methylthallium, Tl(CH 3 ) x, has been prepared. To find its formula, 0.102 g is reacted with HCl. The hydrogen atom of the acid combines with CH 3 to form methane gas (CH 4 ). The isolated methane gas has a pressure of 90.6 mm Hg in a volume of 256 ml at 30.0 o C. What is the correct formula of methylthallium? [7] CMY 127 Examination / Eksamen 4/10 2012
2.2 'n Stroop wat in die voedsel-inmaakbedryf gebruik word, is 'n 19.5 % (massa per massa) oplossing van sukrose (C 12 H 22 O 11 ) in water. By 25 C is die digtheid van die stroop 1.23 g.cm 3. 2.2 A syrup used in the food canning industry is a 19.5 % (mass per mass) solution of sucrose (C 12 H 22 O 11 ) in water. At 25 C, the density of this syrup is 1.23 g.cm 3. 2.2.1 Bereken die molaliteit van die stroop by 25 C. [4] 2.2.1 Calculate the molality of this syrup at 25 C.[4] 2.2.2 Bereken die molbreuk van die sukrose in die stroop. [2] 2.2.2 Calculate the mole fraction of the sucrose in the syrup. [2] CMY 127 Examination / Eksamen 5/10 2012
Vraag 3: Struktuur en benamings van organiese verbindings Question 3: Structure and nomenclature of organic compounds [8] 3.1 Teken n lynstruktuur met duidelike uitbeelding van die stereochemie van (3S,4S)-4-hidroksi-3,5- dimetielheksanoësuur. Draw a line structure clearly showing the stereochemistry of (3S,4S)-4-hydroxy-3,5- dimethylhexanoic acid. (4) 3.2 Gebruik die Cahn-Ingold-Prelog sisteem om die geometrie van die gegewe verbinding te bepaal. Toon die atome en atoomgetalle wanneer jy een binding op n slag vanaf die C-C dubbelbinding beweeg. Wys ook die relatiewe prioriteite van die groepe. (Brei die gegewe templaat uit indien nodig.) Use the Cahn-Ingold-Prelog system to determine the geometry of the given compound. Show atoms and atomic numbers as you proceed from the C-C double bond one bond at a time. Also show the relative priorities of the groups. (Expand the given template as needed.) (4) Geometrie / Geometry :.. CMY 127 Examination / Eksamen 6/10 2012
Vraag 4: Stereochemie en suikers Question 4: Stereochemistry and sugars [18] 4.1.1 Teken beide n lynstruktuur en n Newmanprojeksie, met afkortings vir die alkielgroepe, van die mees stabiele konformasie van 2,2,5,5-tetrametielheksaan soos gesien van C-3 na C-4. Draw both a line structure and a Newman projection, using an abbreviation for the alkyl groups, of the most stable conformation of 2,2,5,5-tetramethylhexane as seen from C-3 to C-4. (3) Lynstruktuur / Line structure Newman projeksie / projection 4.1.2 Wat is die oriëntasie van die alkielgroepe relatief tot mekaar in hierdie konformasie? What is the relationship of the alkyl groups relative to each other in this conformation? Antwoord / Answer:... (1) 4.2.1 Teken n diastereomeer van (2R,3R)-2,3-dibromobutaandioësuur. Draw a diastereomer of (2R,3R)-2,3-dibromobutanedioic acid. (2) HO 2 C Br Br CO 2 H (2R,3R)-2,3-dibromobutaandioësuur (2R,3R)-2,3-dibromobutanedioic acid Diastereomeer Diastereomer 4.2.2 Is die diastereomeer van (2R,3R)-2,3-dibromobutaandioësuur chiraal? Verduidelik jou antwoord. Is the diastereomer of (2R,3R)-2,3-dibromobutanedioic acid chiral? Justify your answer. (2)...... CMY 127 Examination / Eksamen 7/10 2012
4.3.1 Teken die Fischerprojeksie van monosakkaried A hieronder. Wenk: Plaas die karbonielgroep naby aan die bopunt van die tekening. Benaam monosakkaried A. Draw the Fischer projection of monosaccharide A below. Hint: Place the carbonyl group close to the top of the drawing. Name monosaccharide A. (4) HO CH 2 OH O OH A OH OH Naam / Name:... Fischer projeksie / projection 4.3.2 Gebruik die gegewe templaat om die mees-stabiele konformasie van monosakkaried A te teken. Use the given template to draw the most stable conformation of monosaccharide A. (3) 4.3.3 Gebruik n Fischerprojeksie om die enantiomeer van monosakkaried A te teken en benaam dit. Use a Fischer projection to draw the enantiomer of monosaccharide A and name it. (3) Fischer projeksie / projection Naam / Name:... CMY 127 Examination / Eksamen 8/10 2012
Vraag 5: Reaksies en meganismes van organiese verbindings Question 5: Reactions and mechanisms of organic compounds [16] 5.1 Stel n meganisme voor vir die reaksie van waterstofbromiedgas met 2-metiel-2-buteen. Toon die struktuur van die tussenstowwe en gebruik geboë pyle om elektronbeweging in elke stap aan te dui. Wat is die aard van die reagense en tussenstowwe? 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. What is the nature of the reagents and intermediates? (6) 5.2 Watter enkele stel reaksiekondisies sou jy vir die volgende sintetiese omskakeling gebruik? Meganismes word nie vereis nie. What single set of reaction conditions would you use for the following synthetic conversion? Mechanisms are not required. (2) 5.3 Verskaf die ontbrekende reagense en die lynstrukture van die uitgangstowwe en produkte in die volgende reaksies. Provide the missing reagents and line structures of substrates and products for the following reactions. (8) CMY 127 Examination / Eksamen 9/10 2012
CMY 127 Examination / Eksamen 10/10 2012