Exam2_2010_Solutions

Exam2_2010_Solutions - U N I V E R S I T Y O F COLLEGE or...

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Unformatted text preview: U N I V E R S I T Y O F COLLEGE or ARTS AND SCIENCE I DEPARTMENT OF CHEMISTRY Chemistry 131 — Preliminary Exam II 26 October 2010 8:00 am. to 9:30 am. / Name: $06k) .U/ ID #: E ‘ Workshop Meeting Time (day/hour/building) Ed‘qu <3 i) (2 pts. Extra credit) This exam consists of six (6) questions, one extra credit problem, and a page of potentially useful information. Please check BEFORE you begin to make sure that you have a complete exam. Please do all your work on the pages provided. You may use the backside of pages for additional work, but please tell us that you are doing so (i.e. an arrow with a note in clear English saying "more work on back"). SHOW ALL WORK. GIVE UNITS for all answers that require them. Partial credit can only be given for those answers for which work is provided. CIRCLE YOUR ANSWER. We ask this so that we don't have to interpret what you intended as your final answer. Some molecular masses are provided in {}. GOOD LUCK! Prob. w.s. 1(30) 2(25) 3(25) 4(30) 5(30) 6(25) E.C.(5) Total 165 Score University of Rochester Rochester, New York 14627—0216 1) You have four identical 22.42 L super strong and durable flasks (contents and conditions listed below) at a pressure of 1.00 atm. Assume any gasses are ideal. You do not need to show any work. The molar mass of a given molecule or gas mixture is given in parenthesis {}. 1'4 308” K 0 0.3L“ Flask A: 2.538 g12 {253.8} Flask B: 273 (1 N02 {46.01} (9.57%! 9V9 mo\ Flask c: 8.00 g He {4.003} Flask D: 273 K N204 {92.02} 1 mo l \37 K a) (5 pts.) Which flask is at STP? “IQ (STP: 0631037“) b) (5 pts) Which flask's contents have the highest average (i.e. root mean square) velocity? / .75.. amt/VJ];- W War/W flask )4 rear swlld’ c) (5 pts.) Circle the answer for which flask weighs the most? d) (5 pts) Which flask cont '- - ' ctly 0.500 mol of gas molecules? e) (5 pts.) Which flask's con - - -- . 3/}KT’VKE‘ f) (5 pts) Whi lowest average kinetic energy? 0st total atoms? C E ml atams) 2) a) (5 pts) Fargo, North Dakota is a pretty cold place in the winter. Say you blew up some balloons in Fargo for a New Years party to a volume of 2.0 L indoors at a temperature of 22 °C, and then hung them outside where the temperature was -22 °C. Assuming identical atmospheric pressure inside and outside, what is the final volume of the balloons after they have cooled to the outside temperature (assume all gases ideal)? Ingloor: 3 1,}; 2 K BEL: Pvt/1' Pl 3P7. R) 09/490on 173/11. :- D:FSI K (\iTt Viv/TL (mp/)2,“ 1/1: > ’L/Ti or \ VL:L1)(% : L47$Laf ()17L— b) (5 pts) How many mol of gas is inside a single balloon laced outside? Pv:“£r0p n :-_ M _;_,__ Iod'mwlt7 L) : 0‘04“ch ET 009;: )( 25': K) c) (5 pts) Say you poked a small hole in the balloon (without popping it — use tape to do this) and placed the inside and outside balloons in separate evacuated chambers, respectively, that you had lying around your garage. Calculate the ratio of the rates of effusion for the balloons inside to those placed outside. «fire. a? egguéfon 4/ arms or‘ WVj 4/ IOuJ‘ Mciaf MS) Same so F—z————JLI-“i‘€' in Pie : 1 921 Pal-Q, cuts? 6. Tng 951 I; [‘0 d) (5 pts) Consider the J-tube shown below in which mercury was added to the open end to compress an ideal gas in the closed end. If h :167 mm of Hg, what is the pressure of the gas in atmospheres? (assume the experiment was done at sea level) Pregame agUs iv 60%“ka 7L2) “mi/g5 <3“ 2 Mm it e) (5 pts) In one sentence clearly and accurately describe how Nicole tested for the presence of oxygen in the demo where she reacted bleach with a cobalt compound. A/rwza Comm) the oL (07 Ax‘st/«Lemwofi {42,0 in cx “(~63 hate 0mgK [Cl—Q Sfl€n+ (tweak) +0 VQ‘CCT Oz. QT am {Acféase} Jelme (WC litfimey 3) Coal miners used lamps that burned acetylene (before batteries). The acetylene (CZHZ ,{26.1 g/mol}) was produced by reacting calcium carbide {64.1 gfmol} with water as follows: CaC2(s) +H20 (1) —> C2H2 (g)+CaO(s) a) (5 pts) If the coal miner’s lamp on the surface of the earth burns acetylene at a rate of 1.00 L per hour at a temperature of 18 °C, how many mol of acetylene are consumed per hour? (Assume acetylene is an ideal gas) T; 1~ [ 3/ : / K fir Y\ > Z: (/ia)(/tbl Latoya) )(Dfil) ‘ b) (5 ts) However, deep unlerground in a coal mine the atmospheric pressure is 25% larger than at the surface of the earth. Assuming the temperature is unchanged at 18 °C, and assuming the same number of mo] of acetylene consumed (per hour) as at the Earth’s surface, what volume of acetylene is consumed at this higher pressure? P f: I‘ %\K)0‘ :_ It Dds—11% (Age, Pll/ 9% lvd’lfl “L7fll Sb P‘VL9le/L “FF:— nflk T71; \ @OX/co):(b15‘)\/L A L \/7/ — c.6600 MW e) (10 pts) If the typical working s i underground for a coal miner is 4 hours, how many grams of calcium carbide must be loaded into the lamp to ensure that the lamp stays lit for the entire shift? Lam? (amounfié 0,0’4/7 KL/ N3 1 O\/é7é ma] Oxlé7é Mal Cpl—(L mumci-r; O~I€7é Mal Cqél starth l m0\ CLHL @mej 432%. L m\ (QC/L Calm“ 63¢.) 050101,: a/é7é Mo! xémnnéa); (/0753 C49. l d) (5 pts) Calculate the density of the acetylene in the mine and at the surface of the earth in gfL — which is greater? at“ ECU" Cica>up>aw> : M973)" ,. m. 55% @pmmh L y?“ radian 4) (10 pts) Balance the following equation using any method of your choosing: + 3 ’7, +2.4. 0 1"! a + a F o + co _> 1: + CO _ D o ><\\o\< ($033 éfiws (g) e (S) 2 (g) F1Q Lay/Mira: 7 2F: T5147, (lien F5 3% :3:— 3g 6093+HL0 «I; (07, rlHUlq 1 +3— I a _ a t f H D —7 50 9%, Per 5w £3th £2 oiswmérsw *3 '1, , t A rap wt Few/03(5) l” 34a;\ #72. FAQSHM) 11+ éHwD “J— l’ 7‘5 1 b) (10 pts) Balance the following equation in acidic solution: hlorate ion (ClO3') is reduced by the chloride ion producing the diatomic gas chlorine and chlorinedioxide (C102) gas. 99:; Q7 ) +91%» a fli3\i”fl(0103\ \- 9‘4‘ —-> (Janie/N (€405 ~+1H++fi‘—> 610; {e liq/O )1 9%)! E74 +- 1005;;‘7 Hgfl “wozgfl +Cl Ltjh +9*L}'L&é(> c) (10 pts) Balance the following equation in basic solution: r7 ’1 - \ H, ’«l +‘4‘1 Mn04' (aq) + Br‘ (aq) —> Br03' (aq) + MnOz (s) 3; ivmnofw M ‘5 Mao; 4— 255,0 > 1 {kW—34411) N7 (Sn/)3 MHZ/66f Tia/(Matt? 8W? 8r "1—5Hzo 9 Mflzr‘i lily/0+ 3&3‘4/4H‘1‘ l/Vlnflq” +£H+ki€r W A) Mna?’ 1;. LIZ/0+ [graja R ’OHA 9\ o If” amflfmg miner—a matcsi+gofig7,+gm;57wubo Moq‘gfl + 1&ng (8:57} aMn0L¢s\HéH\@1\i’B‘O3@7) 5) Consider the arrangement of bulbs and ideal gases inside them shown below. The volume of and total pressure inside each bulb is given. Note that at 25 °C NO and molecular oxygen react to completion given by the following chemical equation: 2 N0 (g) l 02 (g) —> 2 N02 (g) a) (5 pts) Calculate the moles of NO and 02 before the stopcock is opened. Assume the temperature remains constant at 25 °C, and neglect the volume of the tubing connecting the bulbs. mo 1 By, :@¢‘)CL1¢D\ nob», mm) E 27”” KT @omxmzm) (mommy) 2mm - 0‘03’t7m1 001.: 029817an b) (15 pts) Calculate partial pressure of all gases remaining after the stopcock is opened. Assume the temperature remains constant at 25 °C, and neglect the volume of the tubing connecting the bulbs. Peal/i‘\\W\W~ Mat— (5 [GMT-CU? ‘ ‘ 58/146, \X—«i—akcs PU‘\02/ 7D quCflL W\<9l A/flLPFa&Hl/C& 9 Wl/VO (344:1 Z m 0» we W 0., fix; 05123.3“ ‘9‘- /e/_9fr:_ 0\O%l7 ‘OLOLffl? :1 23%“ L C t joflwxmb gag}! ,_ A POL; o O é‘o L ) 91/02:;lgb— o Ck‘f'm . c) (5 pts) Calculate the total pressure ks after the stopkcock is opened. PD QWP/‘elflii‘ d) (5 pts) What is the mass of 1 mole (i.e. the molar mass) of the gas mixture? Malar— NMSS > A/LJLXOL’l' M/i/ab/M/ob :gmonggf) kQ/étolK‘Bfgl : fl ‘3 6) You and your lab partner place a mixture of carbon disulfide gas and excess molecular oxygen gas in a 10.0 L reaction vessel at a total pressure of 3.00 atm and heat it to 100.0 °C. Unfortunately, your partner accidentally produces a spark that ignites the mixture causing an explosion. Fortunately, the vessel contains the explosion. in which all of the carbon disulfide gas reacts to produce carbon dioxide and sulfur dioxide gases. After cooling the vessel back down to the original temperature of 100 °C, the total pressure of the remaining gases is 2.40 atm. Treat all gases as ideal. a) (5 pts) Write a balanced chemical equation for this reaction. (sags «L when ~> 604% +Q\503(3l b) (5 pts) What is the total number of mo] of gaicbefore the explosion? 9MQT n: P/‘/= : (3‘00 law) a P W W (W ~ “C779érml -— MOLCSQJ/mol 0L 0) (15 pts) Calculate the mass in grams of the carbon di ulfid o 'inally present. fl gem” 3&00200) ’ Tm “- ~ (0 Lo 89—!)(375) Lej‘ Y;1’Y\c\ ngk 7 2 ma\ 0g QMG‘S (D Says X+>/:0k?776 © 3475 007837 : 743/ HR: HEN rm! WKOL \L KO 607, 5 Mo 7, MELMF’F anew“ y * 057357 X : 6t?776 ~0t78’57: Oil75—7 Z J74 ma] CS; Extra Credit Problem (5 pts) Calculate the theoretical number of stages that would be needed to enrich 235 U to 95% purity by means of a series of effusion chambers, using 235 UF6 and 238 UF6 as the gaseous compounds. The natural abundance of 238 U is 99.27% and that of 235 U is 0.72%. The atomic mases of 235 U 238 U and 238 U are 235.04 and 238.05, respectively. Potentially Useful Information e/m = -1/7588 x 10“ C/kg Avogadro's Number, N = 6.02214 x 10 mol' 2X where X = element symbol, A = mass number, Z = charge number Average atomic mass = 2 aiMi ; where ai is the abundance of isotope i having mass Mi Metals tend to lose electrons to become cations, M+,M2+, etc. Pa/PT = xa = na/nT Halides tend to gain electrons to become anions, X' Surface area of a sphere= 4an The mass of N atoms equals the atomic mass in grams Mass of “C = 13.003355 amu Number of moles = sample mass/molecular mass Volume of a sphere= 4/3Jtr3 number of moles of atom X = [sample mass (g)/molecular mass (g/mol)][# mol of X/mol of molecules] M = molarity = moles of solute/liters of solution Mass I3C/mass l2C = 1.0836129 The Gas constant R = 0.08206 L-atm/(mol—K) = 8.3145 J/(mol-K) um =1/8—RMI um = 11% it 760 Torr = 1 atm = 760 mm Hg ppm = volume of gas produced/volume of container For IDEAL gases: PV=nRT , d=PM/RT STP has P 1 atm and T = 273 K = 0°C For 1 mol of gas at STP: V = nRT/P = 22.42 L Dalton's law of partial pressures states P = 2 Pi 5 6 7 8 B C N O 10.81 12.01 14.01 16 00 13 14 15 16 AI Si P 8 26.98 28.09 30.97 32.06 . . 23 24 25 26 27 28 29 30 31 32 33 34 35 36 V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.38 69.72 72.59 74.92 78.96 79.90 83.80 41 42 43 52 Nb Te 127.6 84 P0 (209) 37 38 39 40 44 45 46 47 48 49 50 51 Rb Sr Y Zr Mo Tc Ru Rh Pd Ag Cd |n Sn Sb 85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 55 56 57 72 73 74 75 76 77 78 79 8O 81 82 83 Cs Ba La Hf Ta W Re Os |r Pt Au Hg Tl Pb Bi 132.9 137.3 138.9 178.5 . 183.9 186.2 190.2 192.2 195.1 197.0 200.6 . . . 87 88 89 59 60 64 65 Pr Nd Sm Gd Tb 140.9 144.2 150.4 . 157.3 158.9 97 Ac (223) 226 (227) 91 92 94 95 96 Pa U Pu Am Cm Bk (231) 238.0 (244) (243) (247) (247) (251) ...
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Exam2_2010_Solutions - U N I V E R S I T Y O F COLLEGE or...

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