Chem 315 F09 PS 02 KEY

Chem 315 F09 PS 02 KEY - Chem 315 Due at 5:00 pm. on Fri,...

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Unformatted text preview: Chem 315 Due at 5:00 pm. on Fri, 9/11 [Le (f I) Fall '09 j 3 Problem Set #2 General guidelines: - All calculations must be coherent. ~ All graphs must be reasonably well—drawn or on graph paper. Label axes. 0 Include units on graph labels, throughout calculations and on all final answers. - Report answers to correct number of significant figures. 1. Consider each of the following two reactions: 1. ATP —> ADP + P. AG” = —30.5 kJ/mol 2. glucose 6—phosphate —> glucose + Pi AG’o = —13.8 kJ/mol Based on the above two reactions and their associated standard free energy values, determine the standard free-energy change (AG’°) for this process: K A (r p: a 3 0‘ 3. ATP + glucose —> glucose 6—phosphate + ADP 2. The amino acid glycine is often used as the main ingredient of a buffer 1 . he amino group of glycine, which has a pKa of 9.6, can exist either in the protonated form (—NH3+) or as the free base (—NH2) because of the reversible equilibrium R-NH3+ = R-NH2 + H a) In what pH range can glycine be used as an effective buffer due to its amino group? b) In a 0.1 M glycine solution at pH 9.0, what fraction of it is in the protonated -NH3,+ form? (Important Note: When biochemists write out the concentrations of buffer solutions, only the total concentration of the buffer is provided. That is, a “0.1M glycine solution" means that the sum total concentration of the protonated and free- base forms of glycine is 0.1 M.) \A A c) How much 5.0 M KOH must be added to 1.0 L of 0.1 M glycine at pH 9.0 to bring its pH to exactly 10.0? b d) When 99 % of the glycine is in its —NH3+ form, what is the numerical relation between the pH of the solution and the pKa of the amino group? 3. The goal of this problem is to illustrate how buffers work. Calculate pH values and draw the titration curve for the following titrations: a) 500 mL of 0.010 M HCl with 0.010 M KOH. b) 500 mL of 0.010 M acetic acid (pKa 4.76) with 0.010 M KOH. Guidelines: - For both a) and b), show data for a total of 700 mL of added KOH. - As a first step, calculate the pH after successive 100 mL additions of KOH. If the pH does not change too much for a given 100 mL step, there is no need to calculate any points between. However, if the pH jumps dramatically, calculate the pH for enough intermediate points so you can discern the shape of the curve. - Just show one example of each type of calculation. - The titration curve must have labeled, linear axes (pH vs. volume of added KOH). 4. Describe how to prepare 2.00 L of a 250 mM formate buffer, pH 4.00, from a 1.00 M solution of formic acid solution and solid sodium formate. The relevant pKa value and equilibrium reaction are: (H) 0 ll H~C—OH + H20 _— H—C—Oe + H30+ pKa=3.76 a) For flfifieac.él\/0/ Lwfifltr17)m¢£fil a! W [(7% HA (ilgoflyd //3 0r Vlcb d£(§pv v . I 1 I Buf‘F'eaJ/VQ‘ H~Qé+100“133\@:#i , F “'5’ ? 3 KtTLJEEN h/ c) .3? * ‘ , "' ‘ ‘ J J J AT“ PH: 9 80% 13' mommies! 4 0"M5"1°"‘“- k H— x 0-90 =- ozvawl MING - / \~~-..MW...,_......_,__‘._...—..--- ' WW ..... "/5" u ’ MW -.. x .. ' J . ’AT F5440 , 2:.) - I-“ - " Pp; Pbk-lwhj “A ‘9 H1~ ‘3.L+ ‘03P?) ‘9 0H! : [03 9 [*x ‘Do.~{=W{ti£).a.9 '1‘“ = 7 42 >2: 6.18‘H 9/, 0? HA (3) 69 3, (M MAMA 1: mm?) - FISH pHfi‘7(O AMOIOLR‘Nni : O'os.‘°"0& ##J: O‘EMXQCLWI XlL — $0 0h _ . j j G) QMWA+ at: : O‘oswyh“ Oil)ng MA! K‘NH5® 5 Mel; HCI W52 mm; We a Hwy awe Lama ,. bade] Inef/Ec‘l—‘h/ekv, [H3063] ,‘5 plaza/Wind \C/‘onq ' 4 “Why rave-NT- cdcq/aj'y‘o.‘ (Lear-e 72% d; e. “hm/6M Cfi [ganja or £00m [0H63[Hg0'9j=/0 / (0:17“ 777 e. 827 H" \J 4/62765 fair: [1km my Mum awey) fl—EWJ : Um]: 0.0/0 m P H;. - /7 {ac/a) I’H «(iv 0.644;? 0‘? 50 AL m/e; /7/c/: (a5001)<a0/0 m/ /r/C/ : 0 005a m/ m ,5 m/u IUQOH‘: (0.0504) 0.0/0 Mo/ N40” 5 Q00050 m/ ,5 Ala/6H H6; + NAOH ~a Ma + [fie-Fore Y‘Xn: 0,0050 aooogo o agTCr- " 0.00900 0.00050 doofij’o 'QOCOEO —0_00950 0,0095 0 aogfifi:0.081/‘1 HC’ 755(— v ;’_I 0,082 PH “7( Fth,’ LH “(fer aflzfln of /~5’0 «L NROH mD/u I'UQOH? 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Chem 315 F09 PS 02 KEY - Chem 315 Due at 5:00 pm. on Fri,...

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