FAKULTEIT INGENIEURSWESE FACULTY OF ENGINEERING

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1 FAKULTEIT INGENIEURSWESE FACULTY OF ENGINEERING Ingenieurschemie 123 Engineering Chemistry 123 Toets (Tweee geleenthei) Test (Secon opportunity) 19 / 04 / 2010 Tysuur / Duration 2 h Volpunte / Full marks 80 Prof EP Jacobs Eksaminator / Examiner Mee-eksaminator / Co-examiner Afeling/ Section A: Prof KG Clarke en/ an Me MJ Janse van Vuuren Afeling/ Section B: Prof JJ Heyns Opgestel / Set Sertifisering / Certification Gemoereer / Moerate Afeling / Section A: Prof KG Clarke Afeling / Section B: Prof EP Jacobs Eksaminator / Examiner Afeling/ Section A: Me MJ Janse van Vuuren Afeling/ Section B: Dr C Esterhuysen Mee-eksaminator / Co-examiner Instruksies 1. Skryf eerste jou naam en stuentenommer op al ie antwoorstukke. 2. Skryf Afeling A en Afeling B uielik regs bo op aparte antwoorboeke en beantwoor Afeling A en Afeling B se vrae in ie onerskeie antwoorboeke. 3. Beantwoor al ie vrae. 4. Sakrekenaars soos voorgeskryf vir ie eerste 2 jaar van ie BIng mag gebruik wor. 5. Slegs ie Perioieke tabel met ie US logo mag gebruik wor. 6. Die punte wor regs van ie vraagnommer in vierkantige hakies aangeui. 7. Die punt wor eurgaans in hierie eksamen as esimale plekhouer gebruik. 8. Bykomene inligting en omskakelingsfaktore is agteraan ie vraestel geheg. 9. Ron ie molêre massas in ie Perioieke Tabel af na 4 beuiene syfers. Instructions 1. First write your name an stuent number on all the answer books. 2. Write Section A an Section B clearly at the top right of separate answer books an answer the questions of Section A an Section B in the appropriate answer books. 3. Answer all the questions. 4. Pocket calculators prescribe for the first 2 years of the BEng may be use. 5. Only the Perioic table with the US logo may be use. 6. The marks are inicate to the right of the question number in square brackets. 7. The perio is use as ecimal place-holer in this exam. 8. Aitional information an conversion factors are attache at the en of the paper. 9. Roun the molar masses in the Perioic Table to 4 significant figures. Toetsweek 2010: Tweee geleenthei Afeling A // Section A 1 7

2 Afeling A/ Section A [Volpunte = 40/ Full Marks = 40] Skryf asseblief Afeling A op ie buitebla van ie toetsboek. Please write Section A on the front cover of the test book. Vraag A1 / Question A1 [6 Punte / 6 Marks] Fourier se wet van hitte geleiing kan gebruik wor om ie hitte oorrag eur n muur te moelleer. Vir n muur met n konstante ikte wor ie tempo van hitte oorrag geefineer as: waar Q / t κ A T warm T kou Q t =κa T warm-t kou = Tempo van hitte oorrag = Termiese geleiing = Area = Temperatuur aan warm kant = Temperatuur aan koue kant = Dikte van ie muur Bepaal ie tempo van hitte oorrag van jou tuin tot ie sitkamer van jou huis inien ie buite temperatuur as 555 o R gemeet wor en ie binne temperatuur 23.2 C is. Die muur van jou sitkamer is 6 uim ik en het n oppervlak area van 20 m 2. Die termiese geleiing van bakstene is BTU/(hr vt F). Doen alle berekeninge eur alle eenhee na basiese SI-eenhee om te skakel. Fourier s law of heat conuction can be use to moel heat transfer through a wall. For a wall of constant thickness, the rate of heat transfer is efine as: where Q / t κ A T hot T col = Rate of heat transfer = Thermal conuctivity = Area = Temperature on hot sie = Temperature on col sie = Thickness of wall Q t =κa T hot-t col Determine the rate of heat transfer from your garen to the living room of your home if the outsie temperature is measure as 555 o R an the insie temperature is 23.2 C. The wall of your living room is 6 in thick an has a surface area of 20 m 2. The thermal conuctivity of bricks is BTU/(hr ft F). Perform all calculations by converting all units to basic SI units. Toetsweek 2010: Tweee geleenthei Afeling A // Section A 2 7

3 Vraag A2 / Question A2 [10 Punte / 10 Marks] Twee gas siliners wor aan mekaar verbin eur miel van n klep. Siliner A het n volume van m 3 en bevat stikstof gas met n ruk van 11.5 bar (abs). Siliner B bevat 375 g roë ys (vaste CO 2 ) wat toegelaat wor om te sublimeer (m.a.w. gaan oor na gasfase). Die ruk in ie siliner bereik 872 kpa (abs) naat al ie CO 2 gesublimeer het. Die klep wor oopgemaak en ie inhou van ie twee siliners wor toegelaat om te meng. Die temperatuur in ie siliners bly konstant by 23 C voor en na menging. Aannames: - Die volume van ie verbiningspyp en klep is weglaatbaar klein. - Die gasse tree ieaal op. i. Bereken ie finale ruk in ie siliner. (7) ii. Inien ie helfte van ie stikstof nou verwyer wor van ie mengsel, bepaal ie resulterene parsiële rukke van stikstof en CO 2. (3) Two gas cyliners are connecte with a valve. Cyliner A has a volume of m 3 an contains nitrogen gas at a pressure of 11.5 bar (abs). Cyliner B contains 375 g ry ice (soli CO 2 ) which is allowe to sublimate (i.e. transforms to gas phase) an the pressure reaches 872 kpa (abs) when all the CO 2 has sublimate. The valve is opene an the contents of the 2 cyliners are allowe to mix. The temperature in the cyliners remains constant at 23 C before an after mixing. Assumptions: - The volume occupie by the interconnecting piping an valve is negligible. - The gases behave ieally. i. Calculate the final pressure in the cyliners. (7) ii. If half of the nitrogen is now remove from the mixture, etermine the resultant partial pressures of the nitrogen an CO 2. (3) Vraag A3 / Question A3 [14 Punte / 14 Marks] Jy is n ruimtevaarer wat voorberei vir n ruimtewaneling op ie maan om maan erts te versamel. n Klein tenk in ie agterkant van jou pak voorsien jou met suiwer suurstof. Die suurstof in ie tenk is saamgepers tot 1390 psi (meterruk). Die temperatuur in jou pak wor gereguleer om by 21 C te bly. Jy beplan om ie ruimtewaneling in 4h 32 min te voltooi. Bereken ie volume van ie suurstof tenk wat noig is om ie presiese hoeveelhei suurstof vir jou ruimtewaneling te voorsien, inien n ruimtevaarer se suurstof gebruik 0.84 kg/ag is. (Wenk: Beraam ie waare na n maksimum van 3 itterasies.) Data: Van er Waals konstantes vir suurstof is: a= Pa m 6 /mol 2, b=3.18 x 10-5 m 3 /mol. Aannames: - Daar is geen akkumulasie van CO 2 in jou liggaam nie. - Die CO 2 wat geprouseer wor, wor na n aner klein tenk vervoer. Toetsweek 2010: Tweee geleenthei Afeling A // Section A 3 7

4 You are an astronaut preparing for a spacewalk on the moon in orer to collect moon rocks. A small tank in the back of your suit supplies you with pure oxygen. The oxygen within the tank is pressurise to 1390 psi (gauge pressure). The temperature in your suit is regulate to stay at 21 C. You are planning to complete the spacewalk in 4h 32 min. Determine the volume of the oxygen tank require to provie the exact amount of oxygen for your spacewalk, if an astronaut s oxygen consumption is 0.84 kg/ay. (Hint: Estimate the value after a maximum of 3 iterations.) Data: Van er Waals constants for oxygen are: a= Pa m 6 /mol 2, b=3.18 x 10-5 m 3 /mol. Assumptions: - There is no buil-up of CO 2 in your boy. - The prouce CO 2 is transporte to another small tank. Vraag A4 / Question A4 [10 Punte / 10 Marks] Seimentasietenke wor gebruik in watersuiweringsaanlegte om vaste eeltjies, gesuspeneer in water, te laat uitsak. Die seimentasietenk, hieroner geïllustreer, se voerstroom bestaan uit volume % vaste eeltjies in water. n Gekonsentreere vaste eeltjie stroom, bestaane uit 75 massa % vaste eeltjies in water, wor op n vervoerban uitgevoer. n Verhelere water stroom, bestaane uit 33.3 massa % vaste eeltjies, wor eur n oorvloei pyp afgevoer. i. Bereken ie massa water wat in ie verhelere water stroom geprouseer wor vir elke 40 kg van ie gekonsentreere vaste eeltjie stroom. (8) Data: Digthei van vaste eeltjies = 2.35 kg/l Digthei van water = 1 kg/l Voerstroom Gekonsentreere vaste eeltjie stroom Verhelere water stroom ii. Die versagting van water maak ook n belangrike eel van water behaneling uit. Veruielik wat it beteken as water as har beskryf wor en hoe n mens te werk sou gaan om it te versag. (2) Toetsweek 2010: Tweee geleenthei Afeling A // Section A 4 7

5 Settling tanks are use in water treatment plants to allow the settling of solis suspene in water. For the settling tank illustrate below, the fee stream consists of volume % solis in water. A concentrate solis stream consisting of 75 mass % solis in water is remove on a conveyor belt. The clarifie water stream consisting of 33.3 mass % solis leaves in the overflow. i. Determine the mass of water prouce in the clarifie water stream for every 40 kg of concentrate solis stream. (8) Data: Density of solis = 2.35 kg/l Density of water = 1 kg/l Fee stream Concentrate solis stream Clarifie water stream ii. The softening of water also forms a crucial part of water treatment. Explain what is meant when water is escribe as har an how one woul go about softening it. (2) Toetsweek 2010: Tweee geleenthei Afeling A // Section A 5 7

6 Bykomene inligting vir Afeling A / Aitional information for Section A Die volgene vergelykings kan soner bewys gebruik wor / The following equations can be use without proof: 1. Ieale gas vergelyking / Ieal gas equation: PV = n R o T Met / with R o = universele gaskonstante / universal gas constant = J/ (mol K) = J/ (kmol K) T = absolute temperatuur / absolute temperature 2. Van er Waals vergelyking / Van er Waals equation: met / with 2 n a P + ( V nb) nr T 2 V = o R o = universele gaskonstante / universal gas constant = J/ (mol K) = J/ (kmol K) T = absolute temperatuur / absolute temperature 3. Van er Waals konstantes vir suurstof / Van er Waals constants for oxygen : a = m 6 Pa/mol 2 b = 3.18 x 10-5 L/mol 4. Parsiële ruk = mol fraksie x totale ruk Partial pressure = mole fraction x total pressure Toetsweek 2010: Tweee geleenthei Afeling A // Section A 6 7

7 NUTTIGE OMSETTINGSFAKTORE / CONVERSION FACTORS Groothei / quantity Ekwivalente waares / Equivalent values Massa / mass 1 kg = g = metrieke ton / metric tonne = lb m = oz 1lb m = 16 oz = g = kg Lengte / length 1 m = 100 cm = mm = 0.001km = uim / inch = vt / ft = y 1 vt / ft = 12 uim / inch = m = mm Volume 1 m 3 = liter / litre = 10 6 cm 3 = vt 3 / ft 3 = imp gall = US gall 1 vt 3 / ft 3 = uim 3 / inch 3 = liter / litre = m 3 Krag / force Druk / pressure Energie / energy Drywing / power 1 N = 1 kg m/s 2 = 10 5 ynes = lb f 1 atm = x 10 5 N/m 2 (Pa) = kpa = bar = 760 mmhg by 0 C (torr) = psi 1 J = 1 N m = 10 7 erg = x 10 7 kw h = cal = ft lb f = x 10 4 Btu 1 W = 1 J/s = cal/s = x 10 3 hp = x 10 4 Btu/s Temperatuur/temperature T( F) = 1.8 C + 32 T ( C) = (5/9)( F 32) T (K) = C T( R) = F Toetsweek 2010: Tweee geleenthei Afeling A // Section A 7 7