old final 99 - 14A1F99-F -1- Baur CHEMISTRY 14A LECTURE...

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Unformatted text preview: 14A1F99-F -1- Baur CHEMISTRY 14A LECTURE SECTION 1 FALL QUARTER, 1999 Final Examination Friday, December 17, 1999 Name TA: (check one) (Last) (Fr FINAL GRADE IN COURSE Raquel Hernandez Sundeep Sethi (place an “X” here if you do not wish your Billy Hu_____ Kevin Sheran grade entered) QUESTION NO. CREDIT W 1. There are six questions. Answer each W; write on the backs of sheets if you need more room, but no loose sheets of paper will be accepted. Make sure your exam paper has male pages. 2. Your work must be clearly amazed and legible; credit will not be given for unintelligible responses. 3. Mejngdgmsgnjng must be shown for all computational items; no credit tor merely putting down the answer. 4. Make sure that all answers have the appropriate number of 5. Give units, for all answers, unless dimensionless. 6. Open book examination. Any written or printed materials may be used. 7. DO NOT LIFT THIS COVER SHEET AND BEGIN WORK UNTIL INSTRUCTED TO DO SO! W: H 1.008 O 16.00 Na 22.99 Cl 35.45 Cr 52.00 Br 79.90 He 4.003 F 19.00 Mg 24.30 Ar 39.95 Fe 55.85 Ag107.87 C 12.01 Ne 20.18 S 32.06 K 39.10 Cu 63.55 | 126.90 N 14.01 Ca 40.08 Zn 65.39 NA (Avogadro's Number) = 6.022 x 1023 Ideal Gas Law: RV = nRT R = Gas Constant: 0.0821 lit-atm/mol-K = 8.31 J/mol-K T(K) = t(°C) + 273.15 h = Planck's Constant = 6.63 x 10-34 J-s c = velocity of light in vacuum = 3.00 x 108 m/s Photon energy: a = hv :- hc/A Bohr formula: En = -2.178 x 1018 (22/n2) J 1 e.v.(electron volt): 1.60 x 10-19J Coulomb energy between two chargesQ1 and 02;; E0 = 2.31 x 10-19 J nm(Q1Q'2/r) (Q in multiples of the elementary charge) The Wand am are on the back of this sheet. RETURN OF THIS EXAMINATION: PLACE 3-33¢ STAMPS IN THE PLACE INDICATED ON THE BACK OF THE EXAM AND PRINT YOUR MAILING ADDRESS. If you do not have your exam mailed back to you, inquire at WGY 4009 about availability for return after January 3, 2000. . -2- MM F99-F Name 1. (50 points). This question consists of five brief items requiring a minimum of computation. Be sure to show our method (set up an equation or give a short explanation). 10 points maximum credit each part. parts are all (a) To produce 1.000 kg (1000 grams) of H2804 (sulfuric acid) from elemental sulfur S, oxygen 02, and water, what is the minimum weight of S needed? W7, 64,304,; M x/m): 32.72J (b) Photon A has wavelength 600 nm. Photon B has just half as much energy as photon A. What is the wavelength of photon B? [As hC/AA :: [6 éwmm 55: :6}; Inc/24M = AC/Agj/O_AK:Z)AJ Awaw (c) A sample of an ideal gas has pressure 2.00 atm. The volume, temperature, and number of moles of the gas are all doubled (multiplied by 2). What is the new pressure of the gas? ’2. $7, 22.7). 7- 7! l l/ l _ q . 1 .. 7,. a. I 3 l , :1 I 7.401» V, , fly; 77/ 7: V I Z 2, Z L 97/- 4.0m: L (d) Are the two molecules sketche'd below geometrical isomers, optical isomers or identical? a I I . . ( f \ W W a? WWW fl J O 4145640940 » \ W 721‘ Mme/w . (e) 100.0 mi of 0.200 M HCl solution is titra ed with 0.400 M NaOH solution. What volume of the NaOH solution is required to reach the equivalence (“stoichiometric”) point? * VAN/1A mg ; l/fimng/B Immfl xblwm xi 3 VB on/acmx/ I : ' 23:50 - . h Vl/B /6D.omfl)l0.yw « 50.0% a , -3- MM F99-F Name_ 2. (65 points) (a) (12 points) Below are four descriptions of electronic states of atoms. For each you are to tell whether the state is the W or anexcjtedm and identify the ueutnaLatom which could be in that electronic state. We W neutLaLatnm .LL-il—— M MM) 14 25 2p 2p 2p 1s J__L_L Edi/5m) 2p 2p 2p 8? .L 1s u _L_L J_ W 7€_=N(%> iL_L__ M 5%) (b) (20 points) A hydrogen atom absorbs a photon of wavelength 1070 nm and is ionized by it; the electron released from the hydrogen atom has kinetic energy 5.0 x 1020 J. What was the principal qganturlr; number of the state the electron was in before it was ejected from the hydrogen atom by the p oton. 34%; W” 24;," .: 1178 lad/BIG, ) +5.03/o'zaf FWW Mme/J7 M215) = A f 8 _3¢ {mm/o m5” /070 x/0‘7/M ..L Lax/0”- d 0,24 477’ ,7./76X/0"3 — 41’- = //.0 . -4- 14A1F99-F Name 2. (Con't.) (c) (15 points) Briefly discuss the bonding, electron and skeletal geometry, and orbital hybridization in the three species CH4 (methane), CH3+ (a cadmium ion) and CH3- (a m; carbonium ions and carbanions are important intermediate species in organic chemistry. For each draw a Lewis structure (there are no important resonance forms to be considered), describe the electron pair and skeletal geometry and state what the orbital hybridization about the central C atom will be. Be sure to fixeanuestimalte of the H-C-H bond angle for each species. You may not be able to satisfy the octet in a cases CH H $441 209.5“ 5F I 4 ( 7W T WC-t—i \ (86') ‘Y ($09 (d) (18 points) For the three second row diatomic as species, LlC+, MC and HG, calculate the bond order on the basis of the molecular orbital energy evel diagram given in Figure 3.35 of the text on p. 126. On this basis are any of these species likely to be unstable? Also state which, if any. of them are paramagnetic. _ meets: electron mm stable: mastic: Mutation omen L at A/ ’ < LIC+ (2M) (Mr 1'1 :0 No “We W U-lc‘) ’7: me @Afj/(LAAJQEZPTT)! 37:2’17; ‘35 '(56) ' s 14A1F99-F ' ' Name - 3. (45 oints) ' (a) 25 ints) To the left below is a phase diagram for a pure substance 2. You are to answer all this item on the basis of this diagram. . ‘ . What is the physical state (solid, liquid, 1 000_ . gas) of Z in region I UEEUI 2 region ll SOL region Ill Ea 5 (3 points) The boiling temperature of liquid 2 under 1 atm pressure is approximately 350 K (3 points) The lowest pressure at which liquid 2 is stable is (give value) o-ol atm (3 points) Label the triple point on the diagram with a "T" and give its approximate temperature 267 y K and pressure 0 -Q t atm (5 points) Does the melting temperature of solid 2 go up or down as the pressure is increased? “Dow N From this, what can you conclude about the relative %solid and liquid 2 along the melting line? (7 i s) 4.mg,.,,¢_m_l7/am,m M449 . 100 $3) (20 points) The vapor pressure of substance 2 from part (a) above is 0.100 atm at 330 K. uppose 1.00 mole of solid 2 is placed in a closed 250.0 liter container and is then allowed to equilibrate at 330 K. Will all of substance Z be in the gas phase at equilibrium? If not, what other phase will be present? You must give a calculation to support your conclusion. 7; __ fijzr g (man monoéwfiw'l'c")(33m¢) 5W)” 7" - 0:21; ZS‘O.D L. -e 14A1F99-F Name 4. (45 ints) (a) (2% points) When 1.00 mole each of H20 and 00 are placed in a closed flask and are brought toi 1000 K. the following reaction (“water—gas” reaction) comes to equilibrium: _ I120(9) + 60(9) ¢> H2(9) + 002(9) It IS found that 0.578 moles of C02 has been formed at equilibrium. Calculate the equilibrium constants Kc and Kforthis reaction at 1000 K. WOOL; Méa H2 = 0.576 W #20 = W CO ; /'W‘&'55"&'4’g . 2.. ; (or/+2 (4150:. 411+; 41507... __ (0.578); fig, m _ KG €y0)( 4175p) (A2”); /< 2 K M mwc/méaw AWMMALWW. ’ —- «Help 460 Would we be able to increase the amount of 002 formed by changing the volume of the container while keeping the temperature unchanged? Explain briefly. ' MWm/Mm Wammmww (b) (25 points) At 1200 K, Kc for the water-gas reaction of part (a) above is 0.600. lf 1.00 mole each of H20 and of 00 are initially placed in an evacuated 100.0 liter container and brought to equilibrium at 1200 K, what will be the molar amounts of H2(g) and of 002 (g) formed? 47/ 3’4! 3/3 44/110}?pr : .00—75 7:5,” 7:??— / m We / 7— x ‘- - 775 71% l», > , m ’— / /. m, I I 0- {/‘UD’DL 0 é ) ""94 &[ 0,77)" Z: any/0.7757, /: 7737 =a77l'j 707;]??- 0,437 so 2.437% were awn/60; w W. What will be the pressure in the container at equilibrium at 1200 K? p 7 @LT W 417-; Zéo‘fwflq; «fit'l'flw‘f’qm'f—MQ : 0.ll37+o.v57+{7azpo-o.#3721099 “05/37) : $009426 W P} (Z-WM)(D,0?206CJ~T4~/"M‘4)(11032) .~_ M7422? Ewart—W .V _ -7. MM F99-F Name 5. '(60 ints) (a) 20 points) A solution is prepared which contains both lactic acid at a concentration of 0.500 M_and acetic acid, HOAc, at a concentration of 0.200 M. What volume of 0.150 M NaOH solution IS required to just titrate 100.0 ml of this mixed acid solution to the equivalence (“stoichiometric”) point? (Both lactic acid and acetic acid are monoprotic). 11M W552 Mammal gas—unwrazwm =0.7mM W M VA‘MA*I\/A_ =7— l/,3 'Mg‘A/B (/DD.0M)(0\70?)M)()) = V3(0-133M)(l) _ 0.7 _ Va— Meow 67%), 4557M. Given that theKa for ilactic acid is 8.4 x 10-4 and that for acetic acid is 1.8 x 10-5, find the pH of the mixed acid solution described above (before any bamd to it) [WM/M111 flay/LAN WilliimL’xL HZ ’lftl-L- ' ‘ ‘ = .tHIo'L/=’:*“ x1: Lax/0'“, X; 0020; 4013/7‘7‘mezo M, FAL— /.7o. W Nata/Mame» @WWpH ?_ fib’k’ '3 l+++0flc' ,é(afi:a¢;/)=/,gxw'S—= 39:0 10’? aw"? “w? 7} 5o’7 a flay/o‘fl’wjflym‘ W (b) (20 points) it is desired to prepare a solution of the weak monoprotic acid. benzoic acid, such that it will have pH = 3.00. The Ka for benzoic acid is 6.5 x 105. How many moles of benzoic acid should be dissolved per liter of solution to obtain this pH? _ 3 — oo -3 gig - “[flfi;[8‘j= /0 ,n =/.OZX/0 M 17-? X M So X.:£:_’7‘2_._/IMXM-3. 7We 12’ O-wX/o‘vL ,g- T 2 ————-— = r I 1;“! r 7'6»? x 7%} ado/pa K4 é 2‘ —é ( -0.0 _—_ /'W¥/fl _ ' I...- 0 6_‘r¥’0 .? —— 0 5 ’97:— 0.o/54 , c.— 0.0/54’14 What is the percent dissociation of the benzoic acid in this solution? % ; &,&0/ooX/m;é'/75 0.0/54 . . -8- 14A1F99-F Name 5. (Con’t.) (c) (20 points) A buffer solution is to be prepared by dissolving solid NH4Cl (ammonium chloride) in 1.000 liter (1000 ml) of 0.100 M NH3 solution. The buffer solution is to have pH = 9.50. What mass of NH4Cl should be dissolved in the NH3 solution? (MW NH4CI = 53.5) 444064 m+3= Mom Xawzm; 7/00 50 m Mch = 2’7?;010671 3.053214?! 5297 M4 '1 2'75?" If 100.0 mi of 0.500 M HCI (hgrochloric acid) solution is added to the 1000 ml of buffer solution above, what will the final pH ? MOW; O,/0WOLY§J70M 1 5,0523%. m WWam’m Wc’éofA/fié 374443, I W 4/243 Wm‘m‘fl'?WaW%/¥e€: a/m -0.052= 0.650 % M#%+WWM%%M: 0. 055%.“? sa/aé m 9'27+/’}m “‘13 22257—5111 MW) . _ -9- 14A1 F99-F Name 6. (35 points) (a) (15 points) A saturated solution of the slightly soluble ionic compound M2X3 contains 1.5 x 10-3 moles of the compound per 1.00 liter of solution. in solution the compound dissociates according to M2Xa(s) 0 2M3+(BQ) + 3X2'(8Cl) Find Ksp for this compound. ( 2_J 5 .: (M 3+] L K57 L [M IM Swag /. 5‘ )l/o-BW 4M;X3o&aa4a gem My .4) [ll/13:]; Z x/J‘xm ‘3 M = Box/0‘3”, [Yr] ’3 )</.\")t/o'3 M ; ‘74?)00‘3/14 I 2— "I3 u 4}; (am-3) (mo-3f = 6M (b) (20 points) Magnesium hydroxide, Mg(OH)2, is slightly soluble, with Ksp = 1.1 x 1011, so one method to remove M92+ ion from water (in which it contributes to “hardness") is to increase the pH of the water. Suppose a sample of water contains M92+ at a concentration of 0.010 M. If it is desired to LemoYTe790% of the M92+ by precipitating it as the hydroxide, to what pH should the water be rcug t. c9/ f0‘70 14 AW £Mj‘2+juifl4 M‘o.wlom. \ 2. m 74 wow» 3- 443w”; - z 2 —II_ CM 2:, EMF] L_ [0”] [(517 NW” -' ' 0'00” (77)/ [014:] 5 fldfx/O- 70/7‘; 3.?5 PAL: ##7## MM- 724 724 07% WMMfl /flmc%7/-Zx—/d,fl2, ...
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This note was uploaded on 02/08/2012 for the course CHEM 14A 142042200 taught by Professor Lavelle during the Spring '10 term at UCLA.

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old final 99 - 14A1F99-F -1- Baur CHEMISTRY 14A LECTURE...

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