Chem5 Exam2 W08 Key

Chem5 Exam2 W08 Key - Chem 5(10 section Exam#2 Winter 2008...

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Unformatted text preview: Chem 5 (10 section) Exam #2 Winter 2008 2/28/08 Kev Name General instructions: o 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. I- Remember the honor system. No notes, books, stored information in calculators, or external help is allowed. - Use the Space provided for answers. The back of pagesgiiian be;used as scrap paper. Show work for partial credit! Write legibly! -. - There are 14 questions worth 100 total points on this exam_.___qi§Estions are numbered w arenthesesizitjfiii'c'ate the point value of :prior part of a question, make up a Use significant figures where apprijui“ - This exam has 13 pages. If you-Eire rn'l'si about it. . Page1of13 1. (6 points) For the reaction shown below, the reactants were initially present at pressures of: PNO = 98.4 torr and PM = 41.3 torr. At equilibrium the total pressure was 110.5 torr. Calculate Kp for this reaction. 2 NO (9) + Brz (g) ‘1‘ 2 NOBr (9) (Tina—1,4.» t Hts—wt + h : no»; it: nume- M count—lemmai Foo-3,: WM +wlaeoum+~flr lsvuo'kh PB 1 114+er M50 2 l-S‘i “(3"“a’rq PR3 ; Lia [ 1260 : Siege—1 nth é-G%MQ'L)L 2. (5 points) For the endothermic reaction shown, how will the equilibrium position shift for each of the following cases: “it”?! + CH4 (9} + Hz0 (9) ‘1‘ 3 H2 (9) + CO (9) A. Carbon monoxide is removed. SHiFT llGL-‘(T B. Water vapor is added. swtr—T 9%th C. He gas is added (He is non-reacting). L50 EFF-ELT— A'l- cwaf‘v‘vfi— VCrLJ‘I—‘LLE ‘; K‘C’HT [F Mudc 9 (p; D. The temperature is increased. SHTLF'T Rtbtt-T E. The volume of the reaction container is decreased. vi, '9? I smF‘T Lee"? .‘J PageSof‘l3 a 3. (8 points) Calculate the pH of the following solutions: A. 1 mM HCI Vb]: 3 “[03(1$L0H>\ z‘ % B. 0.5 M NaOH C. 1 x 10'10 M HBr 4. (8 points) Indicate if the pH of solutions of the compounds below will be acidic, basic, or neutral. A. HCN Looms Aug .47 ACLDLK B. NaCH3COO A CH,’C.CJO_ backtr— Mm; -—=> B ELK c NH CH coo “‘“M ; quu”‘” . ._ o — ._ ..—--— : . 4 3 caug- —0\JL‘ALL «cu; K0. I S-G‘HU‘ A‘- K° mum” - uLfiJ'fiZk‘L 54(11— oabuwfih wax E. NaF F— wane {bk-ae- r-“'> 90%“ F. \é‘a __ mo“ _ -u Ac.ch V- A) ; if": : l 5‘th (“6*”) Page 4 of 13 5. (12 points) You are titrating 100 ml a solution of 100 mM sodium acetate (NaCH3COO) with 0.05 M HCI. Calculate the pH after the following volumes of HCI have been added: A.Om| B. 100. ml D. 200. ml {Armc— n&o PML-L‘“ E. 220. ml wm‘tC. Gmk'aé a K mm‘“ H__________ atfiycocr“ + HLQ "7&5 CHECOOH‘ -t (SH 5‘ Hmqu " . M _‘o IL 01 Ht +\£ .: §.G%‘HO C —‘-I. G o l A; ‘L )6 L A” if :§.e‘suc3 I/x EQWW 90M O‘t-F‘tama .45 _ 9‘: [a _ Y‘; Sht‘tw :{ukk} ‘9 [‘3 K? 4H=$fifir : —l03(l-%uu'5 : Hag H” r__,___.. H's-6% «L. os'n " 1-3 Md‘ Hf lOmwkM’ —:?3NMHT: lsmtAfi-fi 1.? '1_§H_,\ HAL = K L 2 Ln »0 “1‘5’ ?l4pq*05 '15 5' L111; -1 EMIUMVCE Faun—rt (HAL? : [Dru-.01 (Wu-JL 3 3.31m) M HAL.- Té: Uta: +AK.’ *1. F - —‘lk V» F "“F 1 flaws 3 END 3 gfldl Fig #1 oqémub \R .— ux L3: L3-“‘ 3W- M.LO R’Fobt (9 (ff low-1L Beams 9th luv-WA HT _______‘___ glen-i 10% {x OvOSh -3 : En: N0 9H : Page 5 of 13 G. Sketch the titration curve (i.e. pH vs. ml HCI added) for this experiment. Page 6 of 13 6. (6 points) You wish to make 500 ml of 50 mM phosphate buffer at pH 7.0. On hand you have 100 mM stock solutions of Na3PO4, NazHPO4, NaH2P04 and as much water as you might need. How do you do this? Note: in a 50 mM phosphate buffer, the total concentration of ail forms of phosphate sums to 50 mM. 056 KaL i’thcssbimtc. Amt) ~. Kfi 1 Llano"? flick; 1-21 'L HIPOH‘ '9: w + we.“ was .4. * Saar-J. OF cuss“ aims)?er -——3 .02? Haws W L151 x: HOLES- A‘ LrtE‘ETX'Q GHQ-Lg -xk : MUS HA WET/M) (MI E)“ : i’u‘t”t [‘3 [M] _ x 1'0 :_ q.2_\ +10) o_°-1$-_x 7k .614 7* to bflls_x X CHEF-i ‘— 0.02SfiK OJmSfl .. ohflv‘ ” ‘1‘ o _Qm”‘4 : 1.61} 7h 7. (8 points) The principle equilibrium in a solution of NaHC03 is: HCO3‘ (an + HCO3_(aq) ~——‘ H2CO3 (aq) + C032- (aq) A. Calculate the value of the equilibrium constant for this reaction. - 1‘ .. fifiHo" Nico} “=1;- uj + CD‘S Ken. ' u‘ 1—; — . . {lice _ t 4:2.3140“ WW3; Hit :— 3 l/ig1 .. {ammo H , A. is s. a. K... >6sz ' : l.l we“ r_.———— B. At equilibrium, what is the relationship between [H2C03] and [CO32‘]? 642C031 1 (9031,] C. Using the equilibrium: {WT [20 31-1 (“10" 31 and the result from part B, derive an expression for the pH of the solution in terms of K31 and K32 (you must show your derivation to receive full credit). H2CO3 (ea) ‘3‘ 2 H+ (an + C032, (as) K ; Nico} :3 H“ 1 14:03“ \CM Hco; :3? Hi 4 C03“ Kali than) '2? 2H" ~i CD31" \C: Ken-Kn “[Uj(H‘—ll 7- ““UfiKQ‘ "‘ L‘jv‘fiL D. What is the pH of a solution of NaHC03? Does this pH vary with concentration? cw a w-KL : M' f (B L Page 8 of 13 8. (7 points) A. Calculate the enthalpies of reaction for the combustion of C2H6, C2H4, and CZHE. ‘7 LCD). ‘1' Buxo ,- AHHU '— [2(—%‘13.$\) k 3(—111.$1)\ .— (._ $41 _(,‘5 -l; "_' __ Cli’rv. +30; ~—-7 ’ZCUL + ZHLQ ISM“... : [2(-3‘L3.Sq +1(“_ZLH_W_)1 q ($11133 ___ fl ‘gzzfik‘s_wv{_,.t 5 (1“; *LOL ’>H{L~u-J 1 [2(4‘13‘51) - Z‘uszfl ~1'ZQ-73 : EZSHUZ B. Based on your results, rank the three compounds in terms of fuel efficiency (i.e. energy released per mole). a? loo; 4: 1410 4mm:— K5 WE S-bd gum 5 CILJL.I \ w W > C2“; 9. (6 points) Assume SplendaTM is produced by the reaction shown below. Calculate the enthalpy change of this reaction. Note: the three OH groups replaced by Cl's are bound to carbon atoms. 2 C12H22011 + 3 Clz + 3 H2 = 2 C12H1908C|3 + 6 H20 an‘tit we ( \. X; L = AB. ct - « e 1e c-ou g“ 9 3 w W 5. '5 144* (D L'Ck C, “’3 <6 R3§l lam—4) (n .111ch 9M5 W5 p“ 52, USE _. 1‘s 1130.1, aw; u 6L 3 3 (30193 ) Jr 210% ’“ G 1?}‘6 ' ‘ .2 d—lfitb‘é : r MUG 5% - Lac ‘ - U ._.. 6M. Tgo‘L »%H=*B Y : _GD1VCJ HO“ "(L M” “49‘ 9% k‘ 6 {Us 59306 Pagegof13 7.th 10. (6 points) You mix 50.0 ml of 10.0 M NaCl with 50.0 ml of 2.0 mM CUNO3. Using the reactions shown below, calculate the equilibrium concentrations of the following: Cumin + crm) = Cuckaq) K1 = 1.0 x 102 (aq) + Cl-(aq) ll CuC|2'(aq) K2 = 1.0 x 104 Cum—(am + chm) : @0321“) K3 = 1.0 x 103 cum 1:3. (to;- \<;= mo“ 1 thw flwx A. [CUCI32_] F no as, ,cui — — - -3 v CUCl L 23”“ CAL +Cl \L = I H0 [Cool-5 1 3 _ _; {$6301 '6“ o 5 A : Xi: W3 wk 1‘ 5 43C {140 cm _ \{fi B. [CuCIZ'] ' \. 5?: f c ' : ML) H \- CCU £1 1 ’2. y—F" c.[cU+] _ l [O_L( (veil : Cyci +Cl K - ‘5“ “Litth ex 73 g“? .. Ga Swim CUCN .123 Cui- _t Ci \(i L‘i—L [*{Ov‘f _'_' ..______ Z7140“:i «Ric HWY“ AL K gfl‘ ’\ K(§)_t“‘£\ 1’ ram my ‘63 H Ho" :fcuafl “w”: *2. Page 10 of 13 .z (cf—3 .11. (6 points) Fluoridation of drinking water has dramatically decreased the amount of tooth decay In the United States. The chemistry of this process converts hydroxyapatite (K5,J = 6.8 x 10’“) into fluorapatite (KSp = 1 x 10'“). A. Calculate the solubilities of hydroxyapatite (Ca5(PO4)3OH) and fluorapatite (Ca5(P04)3F) and compare them (i.e. calculate a ratio). (“3(0L1B3OH— “C—Z“ '5 Ca.“ + 3 9013— e cm“ SK 3‘: Y 6—3‘1‘10—2‘ : ($33: (31)} 3C _" ‘l‘R-c‘ x z 23?. 140—? h m a; MMWE H-iu‘c‘d : (S‘l'fiihkfi r, ' HQ Luv”: MU «.3 (,-i$i0 ’“ HUG“ B. Qualitatively, how is the solubility of these compounds affected by lowering the pH of the solution? & eas- . cu“ [tr were was. so LMQ\ Lg, PM. [NMuj gab: g wet-’5 12. (6 points) When we did the thermite demonstration after class, 1 mole of molten iron at a temperature of 1530 °C was produced. If the molten iron had dropped into snow at 0 “(2, what mass would be melted? Assume all of the heat goes into melting the snow and none into raising its temperature. You will need some of the following information: 13H°nm = -849 kJ; Tmp(Fe) = 1530°C; aH°fusion(Fe) = 1.7 k] mol‘l; c°p(Fe(5))= 25.1 J moi"1 K"; AH°Vapm(H20) = 40.7 kJ mol“; pr(H20) = 100°C; c°p(H20(.)) = 75.3] mar1 K'l; c°p(H20(g)) = 33.6 J mol'1 K'l; MW(H20) = 18 g mol'l. Cit = we fl 5/ \ U. I I amaze R Q 1520 + 01K Fem Q L ,. (G‘Qk'swlifl Y. Wt Deal 1k [33: Le'SMi iwifizsdfifix‘t“ K 1370“ “ «L? m _ :fi‘é H WT .— my? 9’56“ : “(3 fig Kr ‘ M/V“ Page 11 0H3 31c: 13. (6 points) The combustion of gasoline vapor and air in the cylinder (volume = 40 cm3) of a car engine releases 950. J. If all of this energy is converted into work pushing back the piston of the cylinder, calculate the final volume of the cylinder if the gas expands against a constant pressure of 700. torr. m : JQH M1 fl?) : aflvrh VF '- m L) ‘i'o’S fi-t’hmfl-ah qc’oh‘a - 3 .f__ {'3' k ,_ _ 6,011! «Br/I (VP ’ 1’“) -6136: L-ou « 0211/ : niofilll V-P- + ,GQJG“ Vg; \/ 14. (10 points) In two different thought experiments, 1.0 mole of an ideal gas at an initial pressure of 10.0 atm and volume of 1.0 L is expanded either: a) reversibly and isothermally to a final pressure of1.0 atm, or b) reversibly and adiabatically to a final pressure of 1.0 atm. \2. "D :6 (9 :\ raj ($23” / ' ‘fi ‘31- A. Draw a singie P vs. V plot showing both of these expansions and label them accordingly. ( to (Problem 14 continues...) Page 12 of 13 B. Calculate the final temperature of the gas for each expansion. T v {U k : ffi—K I .3 c ,H F‘ MWIL flpi > I K Y Fl , I am . X9 3 r [O " w r tics s \L M leu> r3:— shzgm‘: 1M0 C. Calculate the change in energy AU, change in enthalpy fiH, work (w) and heat (q) for each Path. lg :' 49 13mm: AU :0 A“ =0 l w : amt“! CL: hm mtkaamc -. AL.) : “.3;ng m _._ 6U .. CL : Jim 3 s a v3 23;?“ D. On your plot, draw the most direct path between the end state of the adiabatic expansion'a'ndiithe \ end state of the isothermal expansion. What is happening to the gas as it follows this new path? Calculate AU, AH, w and q for this path. we (Ms. amt-s go “[0 11mm A—T LOLA"; WT P " [aka — l 5:; 415w: so — L R (m 3 .: + Cilia-"'3‘ . ,fl'3:;[‘5}(101-'3 "SIEJMB : «GIGS w ._ : CU: n C? AT I l (She—\(utt #155.“ _ I II T“ _: \g’l") F84 Page 13 of13 ...
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Chem5 Exam2 W08 Key - Chem 5(10 section Exam#2 Winter 2008...

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