CHM 131 - Final - 2004 Key

CHM 131 - Final - 2004 Key - U N I V E i l F COLLEGE OF...

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Unformatted text preview: U N I V E i l F COLLEGE OF ARTS AND SCIENCE ROCHESTER DEPWOFWRY Chemistry 131 — Final Exam 18 December 2004 1 8:30 am. to 11:00 am. Name: K l \ ID #: /§ 2Q [53 This exam consists of ten (10) 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 bac "). 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_o_t_ 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 1123 be given for answers that appear out of nowhere due to a fancy calculator. Assume all gases are ideal. GOOD LUCK and HAPPY HOLIDAYS! Prob. {1(30) §2(25) {3(25) 4(30) i 5(25) 3665)"?E ' F , " I a "1 z y g Prob. .{7(30) {8(30) '2 9(30) 210(40) 3’5545) l «—-——-~r « «a e ~~ ;- r—w — I Score University of Rochester Rochester, New York 14627-0216 1) The following calculations can be done either without a calculator or NOT need to show calculations. For the following pro ' has a Ka = 1.0 x 10's. (4 ts each) P PH: /:‘3 m— PKq: ff}? /\0' b) Youmix40.0 gNaOH (m.w.=40.0) with enocigh H20 to eal.00Lsolution: pH I t . a0 fl\oi : lmoi [mo :: VOHr—Jo @Hj : “)0 :0 ‘7/003/1/l “1% 7,03 f; I IL/O :3 j POHZO >9 “00 ’ ' c) Youmix4.0 gNaOH (m.w.=40.0) with1.00Lofa 0.2MHAsolution: pH — ’2' mm P +- H ‘5 O "’ 9‘0 “OH—70le '4” 6‘ OHemHfil 3.1M H1 +5 @g—M HA :7 £200li pf: o.lm\ «-- .2 0" CH7?) / d) Youmix4.0 gNaOH (m.w.=40.0) with 1.00Lofa 0.2MHN03 solution: pH=€ LO . P iéx. Sane, nix-mm a5 (a) H++OH‘T>/7/7/O 9115A : oil/Vt & \ o s. Mt) ’ O O i > FH;—\03<:Qa :— i .0 Hfl/ ‘ S+ron 03 Ls Q ogfgx Ar“ OthaK "‘ e) Consider a solution of 2.0 M HNOz and 1.0 M NaNOz Circle the correct answer. The solution is not a buffer [OH'] > [H+] (1), (2) and (3) are false i) Consider a solution of 2.0 M CH3NH2 and 1.0 M CH3NH3C1. Circle the correct answer. The solution is not a bufier pH < 7.00. (1), (2) and (3) are false g) (3 pts) I orin an weak acid—base e uilibrium rocesses, which saturated solution has the . - - c7 h1ghest concentration of sulfide lons. ,_ I mafik R 5? Zinc Sulfide Lead Sulfide Nickel Sulfide: All the same h) (3 pts) I orin an weak acid-base e uilibrium recesses, which solution has the highest concentration of total ions? ’— Pfl y-k-fbn E/colfo/y +95 7 [Hi hat/C, 1 ‘29 “5 Sodium Sulfide All the same Sodium Chloride Sodium Nitrate 2 The chemical equation describing the dissolution of PbC12 in water is given by: PbC12(s) s Pb2+ (aq) + 2 c1' (aq) a) (4 pts) What is the expression for KSp for this reacti(51(i.e. law of mass action)? K5? : C Pb”) Co I ’3 ‘\ Geo/5" F5 b) (6 pts) Calculate the KSp value for PbClz, which has a solubility of dmol/L at 300 K. I e 5 : It 6 75%;): /,L , em» Somali—rem 5 PW} : was? Cor) : 2.0.0157/6 /*~"§ .0 157 ) c) (4 pts) If you lower the pH of the solution (from parts (a) — (c)) will the solubility of the PbC12 (circle the correct answer) C I ” [‘5 & SPSEifg—{Pf Increase Decrease Stay the Same Not Enough Information d) (4 pts) If you add some NaCl(s) to the aqueous solution (fiom parts (a) —— (c)) will the solubilit of the PbC12 (circle the correct answer) w~ ComMOfl C0“ gg’gcoi- / qu‘lfz Er Increase Stay the Same Not Enough Information e) (7 pts) The element rhenium (Re) has two naturally occurring isotopes, 185 Re and 187Re, with an average atomic mass of 186.207 amu. Rhenium is 62.60% “‘7Re and the atomi weer ‘87 e is 186.956 amu. Calculate the mass of 185 Re. {1 x ’a '" W “N 761%,) i—UWW Effie) ’— Cfit} )(I #06260) Jr Q6é.?5g)¢g;go> 3 P75 M .— 26620 r”; 107 7 (C(57) +— “103% 3) You are fascinated by some of the ingredients in your too solution sodium fluorid . ' a) (5 pts) Write a balanced net ionic equation for the hydrolysis (i.e. reaction with water) of sodium fluoride. b) (5 pts) Write an expression for the equilibrium constant for this reaction. c) (15 pts) Your sodium fluoride solution consists of 2.00 mol of sodium fluoride that you added to a flask of pure water such that the total volume is 250 mL. What is the pH of this solution? 3) You are fascinated by some of the ingredients in your toothpaste up a solution sodium fluoride. ' quation for the hydrolysis (iie. reaction with water) of a) (5 pts) Write a balanced net ionic 6 sodium fluoride. _ . . . — pg?) + Hzom . ’3» H Fm + OH 8?) Sh“ . Hipl F- I 800 L,_,/—3 ‘2. K1,: X /800-—X: K r‘ N 1|??? Log "S \ C6H1206) to ethanol (C2H50H) and carbon 4a) (5 pts) In alcohol fermentation yeast converts glucose ( n assuming it takes place at 293 K dioxide. Write a balanced chemical equation for this reactio C6H1L06<§\3 fl? QCLHsoHCZW 01407135 b) (10 pts) If 5.97 g of glucose is reacted and 1.44 L of carbon dioxide are collected at 293 K and . 8 a wha is he ercen ield of reac 'on? ,, wilt?" as: := 131.0{gm—@LOOS/Ylflq/AOGWQ : u 34.01 51?.73,t/WS/‘lfl/mol j 0‘0330 m0\ CéHlZOA e i ‘S 67”“ Pv: ART J n: PV/fiT : aofgymfl \ ,. w”- (OOVRIXQHSX \ 5W; 9"“ he” a“ thi so rm 64qu 2&1: Themko VIC/05: LZLKOtOSZQ': 0064 WA E76” \ fl kw .. 22%.: 0.3%: 1’ leg. : / _/ 7 flCOfc‘l‘tCa l 0‘ 066 37‘ 2 7t}, @ 5) You have two bulbs connected by a stopcock at 300 K In one 4.0 L bulb you place chlorine gas at a pressure of 0.5 atm, neon at a pressure of 1 atm, and helium at a pressure of 0.25 atm. The other 2.0 L bulb is evacuated. He, 0.25 atm Ne, 1.00 atm a) (3 pts) Initially the stopcock is closed. What is the total pressure in the left bulb in atm? el' 3 ?ad' Ric)" mo 7' \\7§a+m b) (13 pts) What is the partial pressure in atm of all the gases after the stopcock is opened? av. « w, <n. mm) Mr GIL pas/P73 r H CR1 ©.§l("l.o\ Z LéioMPJ P \ ‘. (Loomio) :(AOBUQL/‘WQ Egg/pips a? «a- g c) (3 pts) Which (if any) compound has the highest kinetic energy? 30mm: T max/x5 a.“ Mug fie Scng KCAQEL Ewe/5) Imagine that you had a detector in the right flask that could determine the identity of the gas molecules as they occupy that volume. d) (3 pts) Assuming no interactions between the three gasses, which (if any) co detected in the right flask first? Egg” {0 A o< ,QT‘ H - .__/7 P l M ‘3 e) (3 pts) Assuming no interactions between the three W) compound would be detected last? C l L rs k64V\\€$+ ,_ C 1L [.5 [qéfj soda, and the main ingredient in Alka Se . bicarbonate ion acts like an acid or a has . ' 84.00 g/mol) into 500 mL of water. 1 tsp of solid = 5.0 ml and the density of sodium bicarbonate is 2.2 g/ml. a) (5 pts) What is the concentration of bicarbonate ions ignoring any weak equilibrium processes? amuse mHYP. )1 H 3m¢ofx : oilslml MH603:©\13 1413’)“ P otl3l m¢\ HCOJ/OSL’ OrZég/VVLCH'CO Write a balanced net ionic causation for the b) (5 pts) You add a solution of potassium hydroxide. reaction of otassium h droxide with sodium bicarbonate. A 4’ — " p y _ KOH “Lo @XOH (cm L . + - + ~ Campki‘t - Km) to“ erWA/Mefl’f stérl AKEMMET) Hadédt 603 Q7} /l/(’/T OHétfH‘ szbéfi ’5 + 6032511) i c) (10 points) Calculate the pH after adding 100 mL of 0.5 M sodium hydroxide. (Hint — think of the lwxai mo; major species alter the chemistry and figure out what you have here) / 1L 5 0H6?) r HCOs (e7) "7 “7/090 +503 qu\/< L( ’0 3C, o.os~\ otm mo\ 00% mol “’7 0.05m¢\ «« Bu . fl Sal—mt, valetme ac, -—r £601“ ,-Io(s.z.-r”)+/o ; +/ 6 w 0 pH 9% 0:; (Hag; 3 :L @954 0.11/0 :Z/O.;i S d) (5 pts) You dissolve 1 tsp of sodium bicarbonate into 500 mL 0 ‘ wa er, and to that solution you add some aqueous hydrochloric acid. The products of this reaction are carbon dioxide and water. Write a balanced net ionic e nation for this reaction. HC/l if? H;TO\ g,” (L 1; ,3 Ck 5 4/0. \ x ‘ \ \ \ mgr! H‘Ur awgm a Hafiéfl Jr Comm e) (10 points) Calculate the volume of C02 produced at STP afier adding 100 mL 0 hydrochloric acid. __ ' chg (c17\ “a H110 "#20145 \ p fiC‘. 0.05ma\ O\13\mo\ “'— 2? PY-O’. ,’—-‘ O\O<gifl\0 Oxofmoi / 0 RT P; /a1Lm/ 7?; (173 @ 5730 W: nRT—a : ’7 / a iMO\@STP fl O~O§mo\ X: L @ 7a) (15 pts) Balance the following oxidation-reduction reaction in basic solution: H -7. +7 '7' +434 H «'2, 8032' (aq) + Mn04' (aq) '9 SO42” (aq) + M1102 (“‘1) w ' l 1‘ 2H++Qe-)3r‘ avg/«nonaan asog‘fgm a 330:3»4Hhéa} 17%.]? ago “’9 350L119" QWO +H ammo; + 1H? 3 5037‘ y + 3-0 H” e the reaction C0(g) + H20 (g) S C02 (g) + H2(g) has a Kc = 0.4. laced into a 100 L vessel and the mixture was lefi to reac . What is b) (5 pts) At a certain temperatur Exactly 1.00 mol of each gas was p the reaction quotient for this reaction? LOO ma\ { /\ /00 L :— b 0‘ OK mdl /L K: ECOLBEHQ . Q, Co.o\\(oLo\) P ‘ " — : I «.0 ’ ” Q C403 (H19) @toijcatow c) (10 pts) What are the equilibrium concentrations of each gas? a -7 S L 1 j >, i ( CO i’ H10 2:" 60L ‘l/HL LéQiL 97)} _\\ '2. " .; . \~><\ M K:OH”<00\‘ZQ 0 £00 :‘a ’Olé3 c @o\+>()t 001+X 19 g 9/5 (Gob-Kl : (1(7ng + 0,00é32 } \ 1‘ 631% ; lg'éfi’ybflq 2 t Cw):CHLO) : O‘ol23 “Lg: X: 2‘16/0’3M/L —— (5073:1H‘ weaponry; that you should not 8. (30 pts) Various titration problems The concentrations have been chosen such ans. (6 pts each) have to consider the dissociation of water and not have to solve any quadratic equati 0.2 M and you measure an initial pH of a) (6 pts) You have an unknown acid at‘a concentration of 2.72. What is the acid? 0 \ gt /V\ 51E? A“; two [hits ; am 9) PH 1.; 0‘70 ‘ ‘L XL—Wm§i b) (6pts)Youhavea100ml ou1onof01MHOl.WhatisthepH§1fier5.011fl;ol£}M . r “00 . Q. ‘ ‘been added? We, luau/L (00ml “OJ M ’— "who _ - " LP é, Acme) / 0H {— Hocl "9 HLOJ‘" ; Kart /o ‘, ~ : w» . e seed /0 «WA @ P l) limo P e; O gmmfi "‘MO ’7 \ H : 7, :1 ’- .570 A TLC C V; We 17; e, (Lu/(LLZACQ )0 ‘n’f.’ P J I I?) 7 I?! 0‘ afier 7.5 mL of] MNaOH has c) (6 pts) You havi: a 0 ml soluson of 0.1 HOCl. What IS the pH * law“ «now we have 2e§mmel hLOé—l lg? oer been added? Same. as 75 mmol Ocl—fi 3W5 C0 “3,. FHZPkat/bs C” /7I‘té+/03(.Z‘2f :7.’7’5+OH>7 =:: (‘77 > d) (6 pts) You have a 100 ml solution of 0.1 M NH3. What is the pH after 10.0 mL of 1 M HCl ha? l been added? live/have, /0 mM\ NH} era» /0 mmal H‘éel ’17 67011151. 646: )07“ H++WH5 a Mi‘fi A/qu‘ 1‘5 cm @954 Kg: KWth3 :1 5.52 ‘/¢ )1 e e «we ewiwtofiww‘ ’3 Oxml ,a- f‘" ' ‘ \ 'i"§( ("K fCHVD J E GLOW—x 4—K +><’ ’ N5 ~3'é3i/d er ><L 7 1x1 ><L: Wow/of c/7/ ‘ e.o°r/~;< &.0‘7/‘ #4140300 1 m e) (6 pts) You have a 100 ml solution of 0.1 M NH3. What is the pH after 15.0 ml. of 1 M HCl has ' been added? Roma) Hm [5/ /0 m L “CLL'H‘QL.&CS Hm Whig“ We v WC arc, (3051? We szivalmcq Poinl‘)omx’>\w€/ have SMLM Mt 1 5' mmo\ HF legi‘ Ova. 1’ : S‘IO ma\/(O\II§L) : COL/3M 9) Consider the reaction of 19.0 g Zn metal with excess silver nitrite to produce silver metal and zinc nitrite. a) (5 pts) Write a balanced chemical equation for this reaction. Hint: Zn ions usually have an oxidation state 0f+2- +— Q + 20 b) (5 pts) how many mol of Zn met 1 is present initially? f h / (“71032: W X 0.17/MO12A7 c) (15 pts) The reaction is stopped before all the Zn metal has reacted leaving you with 29.0 g of solid ,5 (315 metal which is a combination of Zn metal and Ag metal. Calculate the mass of each metal in the 29.0 2 gmixture. Le/Jr X; mass ZADYLWKHOGLS ><+y:9fi,o @ O-lci/ :: mol 6‘: i‘n fl/OL)L+ mol a? in {A The Soli‘xfi _ mg gm Hm: reqweck : Vt; m4 A307, bwl "‘0\ 2:“ (M01); ’ mf— re“ \13. mo\ A3 proalupegx .y I /7¢ 50 ® '27 035’” :2 6% + <f><m7fi >OJ" 2X+Ot30$y /7.o—-ot3037) 3€Tj© WEE/7E} / g d) (5 pts) What is the percent composition of each element in the 29.0 g mixture? 7 "l‘ ~ 0,5047: 57:71 2R : —/ ~— ‘g‘ 27(0 : [1.3/2 0"173/ : [7733?” 310 10a) (15 pts) Calculate the number of g of Ser (m.w. = 125.62) that can be dissolved in l L of water. . . . . = -10 _,_ 2,-1— _ e an and/base reactions of the fluoride Ion KSp 7.9 X 10 # C Sr 36 F 33 3 YD 3mggcfié) 3 Stan: >+2FC§3 4. «o 7 w stzcsms)‘: 1753 Am C *5 +25 —-/0 \ E s as : 7.9m ® 3 S m¢>\ /L 0'9 SFFL S: l0«776/°)/7 —— ACSSOM/CS S: 5.8; 75 Hm¢\ /L X Igaélj/mal ~ 13 6 , 6> (1073 3/; : 502121th ,,> 9PM properties of the fluoride ion, would the solubility of Ser be b) (5 pts) Now including the acid/base greater, less or unchanged from your answer to (a)? + H LO :4; H F + O H .—_~ so Fm C5 'L &l 6'15 r means/‘3 E\\g Sol ukch (r is QCGoL‘l‘CF You will calculate the number f g of Ser t f water bufi'ered at pH = 2.00. c) (5 pts) First, calculate the ratio of by t can be dissolved in 1 L o drofluoric acid to fluoride in Car so—lSItion with a pH = 2./0. CF ~J ’— ___..,——— : "“IJLZ‘: o ._,___. O” 33 CHO ”‘ ma [HFJ p3 /’ , / :; 0 IO '2. “f : 3. (HF) 7; 3 (CFO I 7 , write an expression for the to concentration of fluorlc acid and fluonde. ma‘l‘UCa\ EAcMLQ $075 al\i’l\¢ F/uorfdiq fixed, Algal/55 musf'C/WJK M9 05 Hl—or F” :7 {:23 :[F “EH F32 = 125.62) that can be dissolved in 1 L of water e) (10 pts) Calculate the number of g of Ser (m.w. buffered at pH = 2.00. 145?: [sent/:31:(5>(CF">>L/@9 /7@ LC) +443 mast, g5 2 [F'j+ I375?) o r (F “.3 2 25/m.7 as L s ,, K59: L5“ 127;) :: S(O.o]?>:>77’/o O 2 3,53 701% moVL ><\ Extra Credit Problem (5 pts) A 2.0-L kettle contains 116 g of boiler scale (CaCO3). How many times would the kettle have to be C? (KSp = 8.7 x 10-9). ompletely filled with distilled‘water to remove all ofthe deposit at 25° lbs 56,: [CQZ+>CCO3L#) am); (a6d36) :3 {Ogil—xgflSI‘ go ’: 5Ck E 5 S O“ 3: G59 3 1517/6 mok/L {m a Del) L Kurt/la ~ €04} glusk AfQéoh/Ej X; L {€376 Hme‘x /;L ' as > \ I I m 1 1 Jr» : AS? me WE/ vc /ao'0?3 \ so x? 81mm: :lég wig 16346 ‘1 75 Potentially Useful Information 1 e/m = —1/7588 x 10 1C/kg Avogadro's Number, N = 6.02214 x 10 mol' 3X where X = element symbol, A = mass number, Z = charge number Average atomic mass = Z; aiM; ; where a; is the abundance of isotope ihaving mass M; Metals tend to lose electrons to become cations, M+,M2+, etc. Halides tend to gain electrons to become anions, 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] 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 —bi Vbz —4ac 2a For the equation ax2 + bx + c = 0, the solution is x = Law of mass action: jA + kB Z [C + mD, K = [C]‘ [D]“‘/([A]j [B]“) THE FOLLOWING ARE VALID AT 25 °C Formula Name 19 MM Eb HCI04 Perchloric acid >> 1 IE‘_ Nitric Acid >> 1 CH3NH2 Methylamine H2804 Sulfinic acid >> 1 CH3CH2NH2 Eth lamine @- HSO4' Hydrogen sulfate 1.2 X 10' C5H5N Pyridine 1.7 x 10' ion HF H drofluoric acid 7.2 x {Oj- C6H5NH2 Aniline m HNo2 Nitrous acid 4.8 x101r m *********** m HC2H302 Acetic acid 1.8 x 10' Formula Name HOCl Hypochlorous acid 3.5 x 10'8 m HCN Hydrocyanic acid 6.2 x 10' ' ch m ******* *************** ******** NiS m Formula Name 322 ZnS 2.5 x 10' NaS >> 1 CdS 1.0 x 10' ‘ NaCI >> 1 Pbs mu NaN03 >> 1 PbSO4 1.3 x 10' AgNO3 >> 1 KNO3 >> 1 FeSO4 >> 1 NaNO2 lill These equations only work some of the time: 1/2 pH = PKa ; pH = (ka[HA]o) ; pH = (pKa1 + pKa2)/2 ; pH = pKa + 10g10([Base]/[Acid]) 16.00 19.00 20.18' 16 17 18 S CI Ar 32.06 35.45 39.95 19 20 21 22 23 24 25 26 27 28 29 30 31 32 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 . Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn 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 1 . 55 56 57 72 73 74 75 76 77 78 79 80 81 82 1 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb 132.9 137.3 138.9 178.5 180.9 163.9 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 89 r Ac 87 F 58 59 60 61 62 63 64 65 66 67 Ce Pr Nd Prn Sm Eu Gd Tb Dy Ho 140.1 140.9 144.2 (145) 150.4 152.0 157.3 158.9 162.5 164.9 90 91 92 93 94 95 96 97 98 99 Th Pa U Np Pu Am Cm Bk Cf Es 232.0 (231) 238.0 (237) (244) (243) (247) (247) (251) (252) ...
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This test prep was uploaded on 04/17/2008 for the course CHM 131 taught by Professor Krugh during the Fall '04 term at Rochester.

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CHM 131 - Final - 2004 Key - U N I V E i l F COLLEGE OF...

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