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Exam 3 Answer Key - CHEM 316 Fall 2007 Dr E...

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Unformatted text preview: CHEM 316 Fall 2007 Dr. E. Binamira-Soriaga EXAM 3 November 8, 2007 Naaaa was F53 ID Number: DIRECTIONS: Write all answers on the test form. Numerical answers should have the proper units and number of significant figures. No credit will be given for numerical answers without solutions to support those answers. Write legibly and in an organized manner. Copyright Binamiru—Soriaga, 2007 1. Indicate in the space provided whether the statement is True (T) or False (F). (20 pts) (a) The solubility of an ionic compound increases as the ionic trength of the solution increases (at least up to ~ 0.5 M) due to the common-ion effect. E (b) Water dissociates to produce 10'7 M H+ and 10'7 M OH‘ when some HBr is added. E (c) The activity coefficient decreases with increasing ionic strength and increasing ionic charge. 1! (cl) The activity coefficient of a neutral molecule is zero. l (e) The pH of a buffer is nearly independent of dilution but the buffer capacity increases as the concentration of buffer increases. (f) Maximum buffer capacity is when pH = [HA]. 1 (g) The approximation made in the Henderson—Hasselbalch equation that [HA] and [A'] are equal to FHA and F A_ , respectively, is not valid in dilute solutions of moderately strong acids and bases. L (h) The isoelectric pH is the pH at which the average charge of the polyprotic species is zero. (i) Two factors that affect buffer pH are ionic strength and temperature. I (j) A species is called amphiprotic if it can donate more than one proton. I 2. (a) Write the chemical reactions whose equilibrium constants are Kb] and Km for a form of the amino acid proline. Note that the structure below is for the fully protonatecl form of proline. The pKa and Ka values for the fully protonated form are also given. (8 pts) (b) Calculate the pH of a 0.150 M solution of the amino acid proline. (8 pts) (C) Draw the structure of the predominant form of proline at pH 12.00. (5 pts) (//\\ a . Praline LNX‘UUi 1.952 (c031; H: x 10-2 ‘H, |<.16$U(N}<13y 2.29 ><10-il :, ____~ «EA {.zmo“)§2- aim-No.15) +0. {2. m 'L)[,. aflo‘l‘f) Chaoj‘ '4 l‘l1X,O—L+ 0"; (l 4 744mm M apt” (5’.va c f .00: y“ (4 d0 2 Hi" yflbtflfifi— '1‘ ‘ [MW 4’ ...’.'. r3 Fr“; 3. (a) How many mL of 0.800 M KOH (MW = 56.10 g/ mol) should be added to 250 mL of 0.750 M phosphoric acid to make 1.00 L of buffer solution with a pH of 3.0? For H3PO4: Ka1,Kaz,Ka3 are 7.11 x 10—3, 6.34 x 10'8 and 4.22 x 10‘“, respectively. (15 pts) (b) If you added the reagents you determined in (a) above and found that you did not get exactly a pH of 3.0, explain how you would really prepare this buffer in the lab. (5 pts) (0 WWW PM) «‘3 Hul’Uf' 4' I430" [4) M4, =2m> Hul’ocr’w‘fifl "9 Wolf?» 3450* Kn; ”‘9 * P00?) 3’4, H 0'L w; 31:9: 46.. {43/10) braiding graft gay 09 % MMM 9H Sowe— m Hs%+/M=I’0‘r' bl. x e wul 0K MUM +9 Wok bum 343.90? «I» OH‘ —> “1. P04? Hy?) cams ml x o -x 'X +X . 'X " X an M OH' L26» 5 my (won’am‘ So we WW W MK é (”MM 4J4» Vuchm) x = 0. law ml 014- 9 owwwlofiwyz. x N M swam ”—— Mame! L f“ (L) #11 vfoomL Kw {:4 [L {NJ-w. PM»; 29 M m'c no?) 204 ml o-WbM $40.!“ wcws EM 911% 44‘ ryfiwlw i} {H AfiSW'MM MM #014; ‘j‘ H dam“ all/(WM I'M Mandel Mun H WWW sow? "0:.ng M” 1/44th garb + A‘balazf‘: Mama/L 4. Calculate the pH, pOH, [CO32‘], [HCO3'], [HZCO3] of a 0.0100 M sodium carbonate (”$03) solution. For H2C03 (carbonic acid) K av K 32 are 4.46 x 10—7 and 4.69 x 10'“, respectively. (20 pts) M100; «3 2NA++ 0032- w — ’ H (460' + 0% =2_°___ 6 24322240 00; + 2702—? ; {40f}! fi fir/r” mag + H40; >HJ03 + on, ’7‘ E.“ L. ' ”/qu [4‘ 44:5? 00PM!“ has: 5“ hIaJ-M wmwhfib 14% #9: £9 V9; C0” J'P ,7 algzleo‘fs Cofin’] r}? Low—J 0 0! [0H] Lou-j: 0.00852 Pow. rt? [oM-j= 2.29 __—..—-——- 0430*}...— of..b..—°o';g? momma» WM L13 -, -9007 ? W W has? [cozrja 0 on» mm: o ooMM 14, W1 WM W [$4601] [0“ “'7 Wflofl‘ ’W, 274‘qu 3% a nus? 5. Calculate the % relative error introduced in neglecting activities in determining the molar solubility of La(IO3)3 in 0.0167 M Ba(N03)2. KSP for La(IO3)3 = 1.0 x 10'“. (15 pts) “(Iaggé 03++ 3T0;— 6) WW+ ach'w‘k‘u 3 Loni": [in ”30114 3*.7) WW MM (79 WW até'u'l‘v‘u ”£01037; '* $231510; aom 20.0%?) = 0.0937! fl: %(@.15a)(2)“+ 0~093Y€')")= 0.091» 0.0; (yr/.4; 0.06, rm»: aw: gym??— l0 W”: [WflergCermflf/am 3 [lame [.2‘1X'0’3M ”(fixes-e“) chbifu WW5 ’7‘?” NJ?’L£’L’ELO;L/w = $102 6. Find the pH of a solution prepared by dissolving all the following compounds in one beaker containing a total volume of 1.00 L: 0.180 mol ClCHZCOOH, 0.020 mol ClCHZCOONa, 0.080 mol HNOB, and 0.080 mol Ca(OH)2. Assume that Ca(OH)2 dissociates completely. Ka for C1CH2COOH is 1.36 x 10‘s. (15 pts) 9480””! MW;MH 00240 mi 01%me 008‘) Mi FWD; 043" ”(A 54/010; mm auuaa—azm + Gama); 0.0%»(4 O-OXoW/i U WpMH 4- OH‘ —--3 CIWLV‘" o_ (3,, MI 0.03m! mozoml '0. on -o-0VWMW 40.0?» 0460 wo/ “'- 0./om{ 9H: [m + W3";— EquwHJ ...
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