Exam3_Solutions_2009

Exam3_Solutions_2009 - I V n I _ COLLEGE OF ARTS ANDSCIENCE...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 8
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 10
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: I V n I _ COLLEGE OF ARTS ANDSCIENCE O( I I ES' I 'l DEPARTMENT or CHEMISTRY Chemistry 131 — Preliminary Exam III 1 December 2009 8:00 am. to 9:30 am. Name: flow/egg f2? ID #: éé 3 m Workshop Meeting Time (day /h0ur /room or bldg) mow” 923g 3°12! (2 pts. Extra credit) This exam consists of six (6) questions, one extra credit problem, and 2 pages 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. If you make any 5% approximations you will n_ot receive credit if the approximation is not valid. Also if you need to use the quadratic formula, you need to SET UP THE CALCULATION and INSERT THE RELEVANT NUMBERS INTO THE FORMULA. Credit will n_ot be given for answers that appear out of nowhere due to a fancy calculator. GOOD LUCK! Prob.- w.s.' 1(30) 2(25) 3(25) 4(30) 5(30). 6(25) E.C.(5) ' Total University of Rochester Rochester, New York 14627-0216 1) Consider the following reaction: 4NH3 (g) + 5 02 (g) S 4 NO (g) + 6H20(g) + Energy a) (3 pts.) How would the yield of NO be affected if 02 (g) was added to the system? Decrease No Change Not enough information b) (3 pts.) How would the yield of NO be affected if H20(g) was removed from the system? Decrease No Change Not enough information c) (3 pts.) How would the yield of NO be affected if the volume of the container were increased? Decrease No Change Not enough information (1) (3 pts.) How would the yield of NO be affected if the temperature was increased? Increase No Change Not enough information e) (3 pts.) How would the yield of NO be affected if 1 mol of He (g) was added? Increase Decrease No Change Not enough information 1) (3 pts.) How would the yield of NO be affected if the equilibrium constant K decreased? Increase No Change Not enough information Consider the following six aqueous solutions: 9‘9 WA 1.0 M HC2H302/1.0 M KC2H302 1.0 M HOCl WPV 1.0 M NaOH/ 1.0 M KOH 56 \[QQ 1.0 M NH3/ 1.0 M NH4C1 1.0 M HNO3 SA 1.0 M CH3NH3CN We (5% Note: KC2H302, NH4C1, and CH3NH3CN are salts (i.e. strong electrolytes) g) (3 pts.) List the solution with the most total ions in 1.0 L of solution: N40“ / KOH h) (3 pts.) List the solution with the highest pH. Nam / KOH i) (3 pts.) List the solut'on or solutions that are basic. j) (3 pts.) List the solution with the hi hest concentration of H+ ions. HMO3 2) a) (5 pts) The box to the right represents a portion of an HCl solution with a volume of 1.00 x 10”22 L. Each filled circle represents a single H+ molecule, and each filled square a single Cl" molecule. Calculate the [H+] and the pH of this solution. + \ gflwblaulg l \ Y‘ é=lou‘/OL$W\W\(§ X [loci/OvliL (HT) 3 (1033 M 6%: / lofifiH—B : ” b) (2.5 pts) The solution from part (a) is a __ M HCl solutio ‘ OJ)? l v \ Sin e led-@L/fc) (5 pts) What is the [OH'] concentration of the solution in part (a)? : iLOO 1(OHM-l gr 0% use 90%: W 50 (300: [$72 ’ d) (5 pts) Consider the following reaction: [073 H2 (g) + Br2 (g) S 2HBr (g) The value och = 7.9 x 10 at 500 K. With initially: [H2 ]0 = 0.10 mol/L, [Br2 ]o = .025 mol/L, [HBr]o = 100 mol/L cross Write an expression for the equilibrium constant Kc for action. e) (5 pts) For the reaction: 2HBr (g) ‘3 H2 (g) J; Br2 (g) What is Kc ? \ x \ _/ fl \ \chéf‘fie {a KC ._ 7\?(/o\ t) (2.5 pts) What is the reaction quotient Q for the system in part (d)? Q » (mad: (10672 3) You make up a 0.20 M aqueous solution of methylammonium iodide (CH3NH31), which is a salt (i.e. a strong electrolyte). a) (5 pts.) Write a balanced net ionic e nation for the hydrolysis (i.e. reaction with water) of methylammonium iodide. + CHg/l/ngotflel' 2 H3061?) 4" CH$MHL@7) + A or cuwuféfl g? H (can +- CHWHLGRfl b) (5 pts.) Write an expression for the equilibrium constant for this reaction. K65:- CH‘L} [CH3 N “7,1 CUB/U H53 c) (15 pts.) What is the pH of solution (after e uilibrium is re d)? ( v—I [:.‘ K“: EZM : le/of :— ‘/0 Ilqu @ l b Lain/bl + 'L X : Kq : 195th H 3F TE 0‘1 (LO RX L P! i’K r>< oa K a ‘ l (EM La XAAGQ So EELQQS/xo 7 0‘ , Q XLngt57V6la of X: 349% /l/( :CH I ‘ >.§' 0\ ' W + 1' fi 2 QSg‘an—L 05) vii, 3 5(é7 f) @ 0 4) For the equilibrium: PH3BC13 (s) S PH3 (g) + BC13 (g) the equilibrium constant Kp = 0.052 at 60 °C. a) (5 pts) Calculate the value of the equilibrium constant in terms of concentrations Kc for this reaction at 60 °C. KP; KLGQT‘YM‘ A“ :; (Salli; ne+ (onm'tuft ¢2> K) — b?— W i so 094')?” (0.0m; (1731703 ’ - p ts) A ite an ex ression for K for this reaction using the law of ass action. c) (20 pts) 10.0 g of solid PH3BC13 is added to a closed 0.500 L vessel at 60 °C. The vessel is then charged with 0.0128 mol of BC13 (g). What are the equilibrium co centrations of PH3 (g) andBCl3(g)?C‘6(/ly , @0123 , 50 (x)(o\o:15¢+><) : 604/5 XL+O‘OQSL X " '/0 ’ (O .0234) 14.67% 0(636 (/55 > _,. w 10) / X: ~O\025éios030é or X99vl’lgVOm‘7) a [- l9be 1 X : 21f1‘3V53/Vbl {805:1 0‘615éfX? O (2:135) WVL If 5) Citric acid (H3C6H507) is present in citrus fruits and is a triprotic acid. a) (5 pts) Write a complete ionic equation describing the first ionization of citric acid 7 0%r. ,/ “fiéHsoy 6% 1“ “100/ l (’7 51302;?) + HzCé H30 "(Q73 5% of‘HCHrovcefl 231+txt—HH ~ ’\ b) (10 pts) Cbalcfulate the pl—I of a 0;5 M citric acid (acgtéus) solution;6 5/07 617) H3C4H50723 H +1“ng TS KL; 3\'7(/O ((0 t X: GIG/7M I o 5 2” m0 4/ C) - c, SK Hv i'X 57fl/: ($5,: @033: gig; u/ E G‘s-ex X K _ + colon/t4 X2. K1 _ CH+3£HLQHSO7Q),7LIVO’L/ CH 3 . . #— 7 | ’ " ‘ lie/l flit]; 05% L EH gag/5073 t ‘3 ‘ 2: , ’ng g3:— . OPO‘E-K;®7‘L{ 0 ¢ or; «RC X40 NQ3€¢+ Kch’g @ c) (10 pts) Calculate the concentration of citrate ion (C6H5073') in this solution. * ‘ =~ —» + +¢ Mo 7" K ’ H+3CHC4H§O713 gram H‘Lééuscb RH 6 5 7 q’L 3C : $r4M( so LHqHsof‘L: (97,: Wei/‘4 @ - 4 flH 1’2) Hlié H 3’ K43: erli‘kéhlsov3 Ham \ CC 507 e" _ $1307 £H¢4H5073j (Mex CH+3Ccopfim ham @ fil’lCéHfl7b3: “776’s?” ‘PFOMQhox/c 3 “ tam-731mm 7580/10 d) (5 pts) What is the percent ionization of the HC6H5072' ion? _ t K [6 @ionltal‘fon 3: CC6H5073 3: __ aé /b M 6) a) (5 pts) Write complete ionic equations for the dissociation of NaOH in water and for the autoionization of water. @ Mao Wax M7 A/Je7 \ +0 Wenfl I QSFTJ . ix , _ ’ mow-2: Her when @6‘ Mm 3 wow + OH («fl b) (20 pts) Calculate the pH .of a solution that is 1.00 x 10‘7 M NaOH. (A51; :12ch ~ wok “we CW) >/¢00v57/v\ HZO 2:? CG Hp] 3 3‘00 ‘/D‘P>M @ 1‘ how-57 Wow 50 Kw : manor} 2 my”; ‘1 —,— C“ ’ X “X ( Loo 752K moo VB PK) 0 ,1 : 3190 '75 71“ I (3100/57) 1C! X100 MP7) ks E (I‘DOl/0’7AX) (QAOO‘IE‘? @7‘1‘Oo [/61 Bloof{53</+_)<fi:f Ava (5“ ' '7 ‘ ‘7 ‘ >< ~3tOOVD X+Qt00 a) 5 O X X: W +qkt ~Féo+ X: 33/ 8 70" /1/1 LH‘Q = A00 mix 2 M ngflfisu ' ( 6.1875 *) P am Extra Credit Problem (5 pts) Long and tricky — do this after you have completed the rest of the test. . .. Calculate the pH of a solution prepared by mixing equal volumes of 1.00 x 10'4 M HCl and 1.00 x 10" M NH3. SE‘L‘ACOMQ'H7 5C A/eucf—{EA NHBQ’A "9 WHR—gfl ~ 6135qu I L644 «- ’4 (5L )b_vv\o\ ad: I Cfl/HRJYBCD : 0 t5 WD’MS (SE/53% + qua7\ 2’" Wfiévw H‘Zqfl 19; Eric 5%75/6 I 57015” 4/0 (2/0 . X l C~—>( >< y Potentially Useful Information Avogadro's Number, N = 6.02214 x 1023 mol" e/m = -1/7588 x 1011 C/kg 2X where X = element symbol, A = mass number, Z = charge number Average atomic mass = 2i aiMi ; where ai is the abundance of isotope i having mass Mi Metals tend to lose electrons to become cations, M+,M2+, etc. Halides tend to gain electrons to become anions, X" The mass of N atoms equals the atomic mass in grams M = molarity = moles of solute/liters of solution number of moles of atom X = [sample mass (g)/molecular mass (g/mol)][# mol of X/mol of molecules] Number of moles = sample mass/molecular mass The Gas constant R = 0.08206 L-atm/(mol-K) = 8.3145 J/(mol-K) 1 atm = 760 mm Hg = 760 Torr = 101,325 pascal For IDEAL gases: PV=nRT , 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 —b : Vbz — 4ac 2a For the equation ax2 + bx + c = 0, the solution is x = Law of mass action: jA + kB Z to + mD, K = [C]‘ [D]“‘/([A]J [B]k) KP=K(RT)A“ THE FOLLOWING ARE VALID AT 25 °c Formula F_orm_u1a HClO4 Perchloric a01d >>> 1 Ba(OH)2 Barium >>> I —--- HNo3 Nitric Acid KOH Potassium >>>1 Hydroxide HCI H drochloric Acid —— H2804 Sulfuric acid CH3NH2 .38 x10' HCio2 Chlorous Acid CH3CH2NH2 .6 x 10 l 1 HF .8x10' ——— H drocyanic acid ——— ——I3__ — —— The following equations work all of the time: [H+][OH'] = 1.0x10'14 = w; pH = -log10[H+] ; pH + pOH = 14 [5,. 1A-] [H* [H*} E: [HA] [H41- [H*} If". K, = These equations only work some of the time: pH = pKa ; [H8 = (Kw+ Ka[HA]o)“2 ; pH = (pKal + pKa2>/2 ; pH = pKal + log10([Base]/[Acid]) 1 H 1.008 3 Li 6.941 11 Na 5 6 7 8 9 B C N O F 10.81 12.01 14.01 16.00 19.00 13 14 15 16 17 18 Al Si P S Cl Ar 22.99 24.31 26.98 28.09 30.97 32.06 35.45 39.95 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.10 40.08 44.96 47.88 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te l Xe 85.47 87.62 88.91 91.22 92.91 95.94 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57 72 73 74 75 76 77 78 79 8O 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.9 137.3 138.9 178.5 . 183.9 186.2 . 195.1 197.0 200.6 . . 88 89 Ac 87 Fr Ra 59 60 63 64 65 Pr Nd Eu Gd Tb Ho 140.9144.2 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0 91 92 95 96 97 98 99 100 101 102 103 Pa U Pu Am Cm Bk Cf Es Fm Md No Lr 232.0 (231) 238.0 (244) (243) (247) (247) (251) (252) (257) (258) (259) (260) (223) 226 (227) ...
View Full Document

This note was uploaded on 03/23/2011 for the course CHM 131 taught by Professor Krugh during the Fall '04 term at Rochester.

Page1 / 10

Exam3_Solutions_2009 - I V n I _ COLLEGE OF ARTS ANDSCIENCE...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online