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Chem5 Exam1 F05 Key

Chem5 Exam1 F05 Key - f1 Chem 5 Exam#1 Fall 2005 Name KE 1...

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Unformatted text preview: f1 Chem 5 Exam #1 Fall 2005 Name KE 1 General instructions: 1. Don’t panic! Write down what you know and what you need to figure out. Think about all relevant equalities. Make sure to keep track of units. Check your answer and see if it makes sense! Some questions are easier than others, so make sure you look all the questions over. 2. Remember the honor system. No notes, books, stored information in calculators, or external help is allowed. 3. Use the space provided for answers. The back of pages can be used as scrap paper. Show work for partial credit! Write legibly! ‘11 "ii"- it 4. There are 120 total points on this exam. Questions are numbered and parts of questions are lettered Numbers In parentheses indicate the pomt value of the question. If you can not get an answer to a prior part of a question make up a- number and carry on with it. You will not be penalized twice for an incorrect answer. - 5. Use Significant fIgures where appropriate: 6. This exam has 16 pages. If you are mlssmg a page now would be a good time to tell me abouth. - Some useful information (plus see the periodic table at the end): __ —bi\/b2 —-4ac 0 K = -273.2 °C = absolute zero .76 — 2a 1 atm = 760 torr (mm Hg) °c = (“F — 32) l 1.8 Mufltw €5.5l110 (“ll-1"“) Avogadro’s number N 6.02214 x 1023 moil'1 “cm 3‘1 1 ”‘5 (Tic (5026) Gas constant R 0.08206 L atm k'1 mar1 60 ‘6 (mi-Ila) Some strong acids: HCI HN03 H2804 meet (QC, [”0 Some weak acids: HF CH3COOH Page 1 01’16 1. ('10 points) You need to identify a 500.00 ml solution of an unknown strong acid that you found (unlabeled) in the Chem5 lab. To begin, you prepare a standard solution of NaOH by dissolving 32.00 g of NaOH in water and bringing the total volume up to 1.00 liter. You titrate the unknown acid solution until the acid is completely neutralized. This uses 312.50 ml of the NaOH solution. You then add a small amount of aqueous Ba(N03)2 to the neutralized solution and observe a white precipitate forming. You continue to add Ba(N03)2 to the solution, and after adding a total of 200.00 ml. no more precipitate forms A. What is the identity of the unknown strong acid? What was its original concentration? alumni-rm" turn at: IMUBUE gag-M ' $0 hug Misc,“ Z 2 32 m n can -—~——-——‘ "°‘ “W“ ' p.43“ r. ‘ " y x 3 - 3 (10.005de IL 0 3 R mas“ Hum“: 014’ 6 nodes l+* 4" 0317-5—2— 1‘ (1‘ng 025—! J»- “‘901 .1, 2 Nud{ -——3? 2.“;0 { ”‘3‘ X—L‘ (“1.) mi L 0.15 M u? g .LJJE’L l t _ 0.2.3“ H“ *3 2..” EH 0.5 L 1590.. ‘ ,_____" W 04-: g MA (£501 B. What is the identity and dry mass of the precipitate that forms? Pails? ‘5 81 501 “no 042st 50‘ lso GET (3415- ...Ji $.50“ Page 3 of 16 2. ("10) Hydrogen gas can be generated by the reaction shown below. The Kp-for the reaction at 600 K is 1.800 x 10”. If the initial partial pressures are PCH4 = 1.400 atm, PH2O = 2.300 - 1.600 atm, calculate the equilibrium pressures of all four reaction atm, and P00 - components. Be sure to justify whether you can “ignore the x” if you chose to do sol we I l 4' CH4ig) + H20 (9) 3 CO (9) +3 H2 (9) I ”(an 2-300 1'6““ C9 L __ x a»: 4 ‘k t 3 _ ' Lew HR 3?“ f: | How - X 1'3“" X (Learns) 2 sun — " £6qu y 13 "' LB‘i ‘Ho 3 '3 Pa : leer-wet K: 23151.“! M E611 (<So/o) Put, = I litah. PM : i so: P“ 1.1% $10 3. (5) What is the density of the mixture of gases at equilibrium you determined abmi'e- at 600 K? If you did not get an answer for the question above, assume the equilibrium partial pressures are all 1.000 atm. Note, this is not the correct answer for the question above! cunt .. 9 (has) - ,_——— d - NO 9 (ET P1 = 5'3“ “4"! Page4of16 4. (5) For the reactionlused in problems #3 and #4 above, what is the relationship between Kp and K? Please show how you derive your answer. 5. (5) For the three salts shown below, write a balanced acid/base reaction that leads to their formation. (A)NaC| Hu 1? Hand .—-———-7 Ham 1» mega m m er) ) (B)Rb2804 elllbcn-i e 14:50.] ———-—-32H,o f £15,591 é“ C‘tl (a) . Qt) (C) NH4CHacOO (A C‘ 1) E?) Page 5 0f16 B. (10) For the reaction shown below (also used in problem #3). describe what happens to the equilibrium under the following conditions: CH4(g) + H20(g) : C0(a) +3|"'£(o) (A) CO is added at constant temperature and volume. 5H1 FTS LEFT (8) Xe (an unreactive gas) is added at constant temperature and volume. no SHIFT 'Pmfio P's Guam (C) Xe is added at constant temperature and pressure. VvL. ff, ?Armm. Pg ‘L " $H‘F'TS Ruse“? (D) The temperature is increased at constant volume. Ups—aw silt-1 . Herb 1:.) leo-J (F tax-(Dov Ofi—E‘LLOTMMK (E) The volume is increased at constant temperature. VOL ’15 0’0ka M .L I SHIFTS Ktcsvrr Page 6 of 16 7’. (10) The artificial sweetener S'plendaTM is synthesized by modifying sucrose by replacing a certain number of hydroxyl (Le. OH) groups by chlorine (Ci). This modified sugar can not be metabolized (at least, supposedly) by your body and therefore contains no calories. You know that sucrose (MW 342.34 g/mol). a carbohydrate, is 42.10% C and 6.49% H by mass. You also determine that complete combustion of 100 mmol of Splendai‘M produces 528.0 mg of 002 and 171.0 mg of H20. Given this information. determine the molecular formula of Splenda T“. sacrum Nd 3‘11““ 31"" x 05111 C/ link-A & x (3.6)(‘1‘1 “ll-«fl :- |?_ (_ Cw. Hitou -’ 22 I+ x o‘St‘u o/[G : u o \ 59L ...._ . H. “M NH 3-osmjco‘rl‘ :llu—A Q ”‘1le 7 64:11 “-10 k I...‘ 'c‘t "M H J .-.- lsfilvi Lost 3M Hr (M 3M 0) $0..$Pmdcn ‘5 rum-1 CILHI‘I 05‘ Cl} thud) SIXWox; mu: sacrum-3g: l"; Tit-e SUPQQ- SLJ'CEFT News I» SILUM , 03mm IS a. «whee cf?— Gunny; Sat—MUSE, M chi-W. CficUot‘l-nbaikw)’ , Page 7 of‘l6 Note: for the two problems below, the KS referred to are really KW and K3. But, as we have not covered these yet, treat them simply as regular old K’s. Also assume for both problems that the activity of water is 1 and therefore can be ignored in any calculations. 8. (4) The reaction describing the dissociation of water is shown below. If the K for this reaction is 1 x ’10"14 at 25 °C and 1 x 10'13 at 60 0C, is the reaction exothermic or endothermic? Justify your answer. “‘3’“ + H200) j“ H+<aq> + OH-(BQ) IF eta—Mile AT éO'Q I WEN? hurt 35 A Mahdi“ -1 whommg F—fi’ 9. (4) The dissociation reaction of acetic acid is shown below. If the K for this reaction is 1.8x10'5, does the % dissociation of the acid increase or decrease as the initial concentration of acid is decreased from 1.00 M to 0.100 M? Note: the % dissociation of something is defined as the equilibrium concentration of one of the dissociated products divided by the initial concentration of the dissociating reactant. CH3COOH(aq) x——‘ H+(aq) + CHgCOO'(aq) K. <wligsmo'l is em) * (a, ~ x nub-Be {Fun (50114.6 out. - , _ r3 [Hiaé- Luna ’ [H11 .: (A 2 - H.731 ‘t-lo h 0.12%. Dumm- | o (HAL: (Moo '1 , £144? :01 = Lat! no" H ' 1.3% 05W ‘30 psctwRSéS «s aid—3.4 Pages” 1U. (12) Balance the redox reactions shown below. Indicate the oxidation numbers for atoms being oxidized/reduced and show the half reactions. (A) HXGO4( ()aq )—> X8054 (aq) + Xe (g) (acidic conditions) i‘Tl 1“ 1‘ p“é at!” *8 ,1 o 69’ + HKeO-I' —**-~7 fie “WWW @1401 i ““47 Xe 0““ v1- 26*) 3 ‘5“0k1‘“ me + H “€01” “I 3‘90““ in *6 k 8"” Ar 3 (s) < < l 1\ 1‘ T *3 w. Page 9 of "i6 (C) 02 (g) + Sbw "‘2' H202 (aq) + 81302 (aq) (basic conditions) 11‘ T’j T1 0 0 L +9 .4. Page‘lO OMB 11. (‘10) Vanadium and oxygen form a series of compounds with the following compositions: Com-ound ——— (A) What are the relative amounts of oxygen in the compounds for a given mass of vanadium? '13‘1‘3/16“, a 35m [H1 5 | I. ' 2 oSZ‘a/"fl¥ T. .-"'1:f‘ ‘z‘fi I, 'IS 11 5 . 3’. 1% 3/. 611 : ,Q'L“ / .3“ ; 2") ‘1 (B) What are the molecular formulas of the four compounds? IF 1r: :3 \lb “1“” "ant 1*), Vols --—7 V1053 (P. fl} Vol .4537 ‘& -_ kl .VO L's. «rd—“*3 V10? Pagefl 0116 .rwr" d! '12. (10) A mixture containing only NaCi and KCI masses 1.0000 Q. When the mixture is dissolved in water and excess eiiver nitrate is added. an insciuble precipitate of AgCI is formed. if the mass of AgCi formed is 2.1476 9, what were the mass percents of NaCi and K0! in the original mixture? {3.30 mm = m"; .35" was ’1; Ci I 3311’ -. (3.1x? {‘43-'33 .2‘11 (\ -’ 6.5%) (' Cosmo) 4» O-H'?6<|'$> :0~$3 X ; 0}“1 fiqllqufl‘i'cl l, i ; 0.3%: 2-3 $8.3"?qu \ CHECK firs M ' fff—- -——‘——h _ 5' Page 12 of i6 13. (10) In the Fall of1984. the Great Dartmouth Class of 1988 constructed a bonfire for homecoming. it had, of course, 88 tiers, and each tier contained 6 railroad ties that Weighed 40.00 kg each. Assuming the wooden ties were composed entirely of cellulose, a complex carbohydrate with the molecular formula (CH20)n (where n is a really big number), determine (A) the volume (in liters) of 002 produced that evening. (B) This volume of gas would fill a cube how many meters on a side? You should also know that. as not uncommonly happens during the bonfire. it started to snow. So assume the temperature was 35 °F and the barometric pressure was 750 torr. MASS (mouse Page 13 01'16 14. (10) Sketch a graph of the following and label any important features: (A) Pressure versus volume for and ideal gas at constant temperature. \ Pdv V (B) Volume versus temperature for and ideal gas at constant pressure. I O ”fin-i ‘L T (C) Volume versus number of moles for an ideal gas at constant pressure. \ivm Page 14 of ’16 15. (5) WUstite is a nonstoiohiometric oxide of iron with a composition ranging roughiy from F90_3501_00 to Feg,g501.oo depending on how it is synthesized. Calculate the percentage of iron in the iron(l|i) form in a sampie of wE‘Jstite of composition FeagsoOLooo Page 15 of ‘16 ...
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