Spring 2007 midterm1

Spring 2007 midterm1 - 10f2 BIS 102 Name Q Spring 2007 MWF...

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Unformatted text preview: 10f2 BIS 102 Name Q} Spring, 2007 MWF Last First K. Hilt First Midterm Score (100): Equations: pH = pKa + log {[b]/[a]} Ka = 2/(y-x) Kb = x2/ (y-x) pH = (pKa 1 + pKa2)/2 (K,)(Kb) = 1 x 10‘14 F=(q1q2)/sr2 AG=AH-TAS Amino acid pKa’s: (It-carboxyl group (2.1), oc-amino group (9.6) side chains: D (3.9) E (4.2) H (6.0) c (8.3) Y (10.1) K (10.5) R (12.5) Oligopeptide pK.’s: C-terminal carboxyl group (3.6), N—terminal amino group (7.4) 1. (15 pts.) Which amino acid has a net charge of approximately “-0.17” at pH 11.8? Give your reasoning and show all necessary calculations. Then draw the structure of this amino acid that would predominate at thisPH. A‘l’ 91+ ”'5, 5M m ,1' [W 2 6).; W}; W 3mm flu, oLvC—O'OH I 91/.“ MAI +9.2 ohm); Pig. m coup 2"”! my; 1%‘4 [wu/awé . wm’c‘na M w“ 144’ ‘I 0", MW, 5M 5212' M W Le +0.36. 71M cam ava‘a, hi— Mafl‘w‘ke, M ‘174 4., HvI-I “fie Lk H’ .: Kn. +I?Lal 6’ f a we“ Il-3'= 12‘ +/ug,2 ”5'?” 'o 7 c 17 1;; Lab-ls >/ a 7 =/ .fi 11.114 J’ ”5’ b ‘clxeiiuz 5:101 -— 3;. 0»: 2°" : 0.93 “”1 (0‘ 33)(+1) = +0.?3 +7 2. (20 pts.) How many moles of KOH are required to change the pH of 600 ml of 0.100 M g1ycine,'pH 2, to a final pH of 9.80? Show all work. 4— C("”" 2.1 9 $0» . pflqua-i' [Wk/ii 11394144 22—- ?‘4 2— 0" I J?— “ 1 1 aha-«Hick Qui:2 (1114:418’ 0.; = ”’3, ‘21 W +5 1.51": b la: "’7’ - ‘4 z " 2~l + I ’ A ”5/ a— (a. (.12)(a.ab ”2(a): 0.03972 nee—Q a" g [03,? +5 +3 0H“, til LLL = or . = "a" 1': - 3W 2% "'1" ‘E _ a. 344- 0 54 5+“? (9.1,ch 950.1 M 311W): 0.01, we G. L0. s‘b)(o.ob Mae 6) c 04339 Lie 044' raw/Mud .(Lw 11,1111 :- 0. 03342 Make 0+}- ~17 0.03672 ”“4 0H-: p.970 Mae 0).}, +4 20f2 BIS 102 Name ______\ng________________ 3. Imagine that you have two different bottles of 0.10 M phosphate solutions in the refiigerator. Mixing crystals of Na3PO4 into water made one solution. Mixing crystals of NazHPO4 into water made the other solution. The pKa’s for phosphoric acid are 2.12, 7.21 , and 12.32. A biochemist could use these two bottles to make a 0.1 M phosphate buffer solution by simply pouring different amounts of each into a container. Note: no use is made of either HCl or NaOH. One simply uses the two bottles that you have in the , ‘. - _ 7, 12.32 ’ refrigerator. H3 70% 7 '1 ”JD” I l l H ”0‘? z ..-. P04 3 (10 pts.) a) With just these two bottles at your disp<¥al, what is the lowest 2H 0.1 M phosphate solution that you could make? Show all calculations. “A 9H _: 7.2.1 +l2~31 :: 4.76; 7.8‘ ‘1 +3 ' 1(— Von-vw) 9K4]; (10 pts.) b) With just these two bottles at your disposal, what is the i est H 0.1 M phosphate solution that you could make? Show all calculations. Kb : >4 z )4 / L’rfo ~ . 2.04 x /0 " a" k 2,061 [[535 X QKb+ ? VFW ‘2 0H’ 0. x: £9.57 x10 M 5 (’Kb : 1.9? fr —10}K§, [34 .a 'fi . Kb = 2.0? x10 z 90” .., 9” =12.“ 7 ”-7 (15 pts.) c) How would you make up 100 ml of a 0.1 M phosphate buffer, pH 12, using these two bottles? Show all calculations. 7. L P“: (Kk #117} 1g) ‘7, 7. 11.32 + (rm/.5“ «1.32 : lava a .31 -; l w a ”‘1 t. '7 5.?0 b 1: 32.5?0 2.08’cf}. ..,a= 2‘03’ z: (9' ’1‘ b 3.05" +5 {1‘ 4,7.fm1 0.1M Mal-+904 *' 325mg 0"” “‘3”? 4. (30 pts.) Draw the complete structure of a pentapeptide, in the form that would predominate at pH 7, that has the following amino acids in it: one with an amide in its side chain' one with a guanidino ou in its side chain; one with an indole ring in its side chain; ¥e with an imidazole gong in its 1de chain; and one with a thiol group in its sidE chain. 1‘ N ar t w (’7 H K L .) t‘fkb W14. 0 4 ‘3 ‘1' ‘9 ’2’ ‘0’! H” fl em 1 +4 I H I | l —- —— .— —- .—— 'IQ -- 6" ‘- " C’C" N- -C 3 G|H2 C, "t’ i,” c’ A l” C T g“ 5", fig 13 +4 W cavola __ +10 c. c c '- ‘ H‘ L" 2 ‘" 2 H ‘2 N Ll 393 3W 5” C =c\ c=0 a, \ NH ...
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