lc8sol - Jim Lisy - CHEM 204 Spring 2010 1 Homework 8 Due...

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Unformatted text preview: Jim Lisy - CHEM 204 Spring 2010 1 Homework 8 Due date: Fri Mar 19 23:00:00 2010 salt bridge Pb2+ + 2 e‘ —+Pb (s) Ag+ + 1 e‘ —>Ag (s) go = _o.13 V g0 = 0.80 V What is the voltage, at 298 K, of this voltaic cell starting with the following non-standard concentrations: [Pb2+] (aq) : 0.083 M [Ag+] (aq) : 1.01 M Use the Nernst equation: g = :o- (RT/um 1n Q First calculate the value of Q, and enter it into the first answer box. Q is dimensionless. Then calculate f, the non-standard cell potential, and enter its value into the second answer box (remember the unit of§ is Volts). Q: Tries 0/99 5: .‘l Tries 0/99 *5 137031216. +1 ’5’“ Jim Lisy - CHEM 204 Spring 2010 2 Homework 8 Question 4: Use the half—reaction shown below to set up the concen- tration cell as illustrated: Li<sup>+</sup> (aq) + e<sup>-</sup> —>Li (s) §<sup>o</sup> 2 -3.05 V «H 2‘ There are Li (s) electrodes in both beakers. There is also t a salt bridge joining the two beakers and a voltmeter to T V / 7 measure the potential of this concentration cell, at 25° 9 W aw In , I) t c. g £ M , , The beaker on the left contains: [Li<sup>+</sup>] = til ? 0.2 M 1/ fl ‘ (6w- . 2w all/ZN: em The beaker 0n the right contains: [Li<sup>+</sup>] = '2 0.4 M 1.. ” ,.__, “We The initial potential of this concentration cell will be: ea . 4», +o.o\¢6v volts ¢t Tries 0/99 will flow: “2’; k O V A. there Will be no flow of electrons rorn the left beaker to the right beaker "‘7 ‘TL'J L0 .' l\ we. l“ /, C. from the right beaker to the left beaker _& t 60* Ce“ vhfaj, 3 VS “(of Tries 0/99 Jim Lisy ~ CHEM 204 Spring 2010 3 EWEME wwww .mm ............. “W WWWWW ._ fiu3++ 39” ma» Au The picture above shows a setup that could be used for electroplating . \When the Olympic Games were held in Atlanta, the United States provided gold medals for the athletes. Calculate how many grams of gold would be plated, out on a, coin, if a, current of 2.8 (Amp) is applied for 10 min to an electrolytic cell shown above. The following reaction is occurring: A1131” + 3 e“ ~«>Au MW for gold equals 197g / mol. 1 amp (A) 2 1 coulomb/second Charge on 1 mol of electrons : 90500 coulombs (C) x 1 faraday (F) Calculate the number of grains plated out You must take into consideration the number of moles of electrons necessary to reduce each gold ion to gold. Jim Lisy — CHEM 204 Spring 2010 4 Homework 8 Suppose a solution in an electrolytic cell contains the the four ions shown below. If the voltage, which is initially very low, is gradually turned up, in which order will the metals be plated out onto the cathode? L? Zn2+ + 2 e‘ ~>Zn £0 = —0.76 V g Fe3" + 3 e" —>Fe go 2 -0.036 V Tcu2++2e-—>Cu 0:0.34V d) E Cr3" + 3 e" —>Cr £0 2 -0.73 V Tries 0/99 The Nernst equation can be applied to half-reactions. Calculate the reduction potential (at 25°C) of the half-cell Cu/Cu2+ (2.7 (The half-reaction is Cu2+ + 26‘ —> Cu. E0 = 0.34 V) 5- ZS- V T mes 0/99 Calculate the reduction potential (at 25°C) of the half-cell MnO4' (2.00 x 10*1 M) / Mn2+ (6.00 X 10'3 M) at pH = 6.00. (The half—reaction is MnO4' + 8H+ + 5e’ —) M112+ + 4H2O. E“ = 1.51 V) Tries 0/99 An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. What is the potential of this cell at 25°C if the copper electrode is placed in a solution in which [Cu2+] : 5.3 X 10—10 M? Tries 0/99 The copper electrode of the above cell is placed in a solu- tion of unknown [Cu2+]. The measured potcntial at 25°C is 0.113 V. What is [Cu2+] (in mol/L)? (Assume Cu?Jr is reduced.) Ml L" Tm'e 0/99 A calibration curve to show how the cell potential varies with [Cu2+] may be constructed. A plot of cell potential (in V, with the same sense as in question 1) versus log10[Cu2+] should yield a straight line. What is the slope of this line? Tries 0/99 Printed from LON-CAPAOMSU Licensed under GNU General Public License 5’ ., B) Q 2 k i in? m ( 1 7" ) O. ‘54 "T”»~ I m Multh 2‘ 7 Z ‘ 705,3004’ v/rrx/v—r ~ M" ‘7 .. a -\- 0,0‘5 L : CM V fl ’ [Ha/CM] 07»er3 8 L r . ‘ ‘MM r h . {WOLF at": 4440‘ (10:) K , S‘Ig L. , Lg ._ 93231-7: \ogl (3., :Lu —€%—~ (05113160 ) _, ' gigxwmw fi— CD‘ 5 ~,.- :0 LI , , a: U C‘ulk"? 2C, "‘7 Cox Z ’- 05“ ,- 0, . Ht '7 '2 Mch i. r O .»A..~——-~'-T“"""' ' A r ‘4 " / . . finizxéi’v’) “t Hz flank). (“E t' 5 0,7,4 w "‘21P lag“, »l ‘31:? A o H 0-54“Ur27—ic§.(57 u. 3".3KI0" - w a. .os‘az ‘ g2.“ » GLUE» L .3‘(+ 9/“ iambic“ g “7’43? 11¢}va it}; visa) /a.o$‘72. ’1 tea“; 2 2H 5410'“ W 2% Mia loithu .3 \.x ’1.» -/ slap-c 0 [024@ V V9310 t (25) ‘l‘ ...
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This note was uploaded on 11/19/2010 for the course CHEM 204 taught by Professor Gruebele during the Spring '08 term at University of Illinois, Urbana Champaign.

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lc8sol - Jim Lisy - CHEM 204 Spring 2010 1 Homework 8 Due...

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