PLEASE PRINT YOUR NAME IN BLOCK LETTERS. 04/02/09 Last 4 Digits of USC ID:

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1 Chemistry 105 B First Letter of PLEASE PRINT YOUR NAME IN BLOCK LETTERS Exam 3 last Name Name: 04/02/09 Last 4 Digits of USC ID: Dr. Jessica Parr Lab TA s Name: Question Points Score Grader Total 100 Please Sign Below: I certify that I have observed all the rules of Academic Integrity while taking this examination. Signature: Instructions: 1. You must show work to receive credit. 2. If necessary, please continue your solutions on the back of the preceding page (facing you). 3. YOU MUST use black or blue ink. (No pencil, no whiteout, no erasable ink.) 4. There are 8 problems on 11 pages. Please count them before you begin. A periodic table and some useful equations can be found on the last page. 5. Good luck!! =) 1

2 1. (18 pt) Determine whether the following statements are true or false. If false, correct the bold part of the statement to make the statement correct. a. The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is zero. b. When a process is spontaneous it has a rate constant greater than 1 for the direction written. c. All standard reduction potentials are measured relative to the standard water electrode. d. In the redox reaction: 2MnO 4 - (aq) + 6H + (aq) + 5ClO 3 - (aq) 2Mn 2+ (aq) + 3H 2 O (l) + 5ClO 4 - (aq), five electrons are transferred. e. Carbon dating can be used to date all types of material. f. The binding energy for a nucleus is the energy required to break a nucleus into its component nucleons. 2

3 2. (8 pt) For mercury, the enthalpy of vaporization is kj/mol and the entropy of vaporization is J/K*mol. What is the normal boiling point of mercury? 3

4 3. (10 pt) The K b for methylamine (CH 3 NH 2 ) at 25 o C is 4.4 x What is the value of ΔG when [OH - ] = 1.5 x 10-8 M, [CH 3 NH 3 + ] = 5.5 x 10-4 M, and [CH 3 NH 2 ] = M? Will the reaction proceed toward the products or the reactants? Why? 4

5 4. (20 pt) A galvanic cell is based on the following reduction reactions: Co 3+ (aq) + e - Co 2+ (aq) Cr 2 O 7 2- (aq) + 14 H + (aq) + 6e - 2 Cr 3+ (aq) + 7 H 2 O (l) ε o = 1.82 V ε o = 1.33 V a. What is the balanced reaction for this cell? b. What is the standard cell potential for this cell? c. Give the line notation for this cell. d. In a galvanic cell, what is the purpose of the porous disk or salt bridge? e. If the cell is at standard conditions what are the concentrations of the ions in solution? 5

6 f. On the figure below add in the following for the galvanic cell described above: i. The ions in solution in each compartment ii. Label the cathode and anode compartments iii. Label the composition of the electrodes iv. Indicate the direction of electron flow porous disk 6

7 5. (10 pt) A voltaic cell is constructed that uses the following half-cell reactions: Cu + (aq) + e - Cu (s) I 2 (s) + 2 e - 2 I - (aq) ε o = V ε o = V The cell is operated at 298 K with [Cu + ] = 0.25 M and [I - ] = 3.5 M. a. What is the cell potential for this voltaic cell, at these non-standard conditions? b. What is being oxidized at the anode, with these non-standard conditions? c. If the [Cu + ] was equal to 1.50 M, at what concentration of I - would the cell potential be zero? 7

8 6. (10 pt) An aqueous solution of an unknown salt of manganese and chloride is electrolyzed for 1.35 hr with a current of 3.21 A. If 2.22 g of Mn metal is produced at the cathode, what is the formula for the manganese chloride salt? 8

9 7. (14 pt) a. Write the equation for the decay of 241 Am by alpha-particle production. b. 241 Am decays by a series of alpha-particle and beta-particle productions, taking 241 Am through many transformations to get to 209 Bi. In the complete decay series, how many alpha particles and beta particles are produced? alpha-particles beta-particles c. 241 Am has a half-life of years. How long will it take for a g sample to decay to 18.5 % of its original mass? 9

10 8. (10 pt) The binding energy per nucleon for 27 Mg is x J/nucleon. Determine the atomic mass of 27 Mg in amu. Proton Mass Neutron Mass Electron Mass amu amu x 10-4 amu 10

11 I 1 H Li Na K Rb Cs Fr (223) II III IV V VI VII 4 Be Mg Ca Sr Ba Ra Sc Y La Ac Ti Zr Hf Rf 261) 23 V Nb Ta Db (262) 24 Cr Mo W Sg (263) 25 Mn Tc (99) 75 Re Bh (262) 26 Fe Ru Os Hs (265) 27 Co Rh Ir Mt (268) 28 Ni Pd Pt Ds (271) 29 Cu Ag Au Rg (272) 30 Zn Cd Hg Uub 5 B Al Ga In Tl Uut 6 C Si Ge Sn Pb Uuq 7 N P As Sb Bi Uup 8 O S Se Te Po (209) 9 F Cl Br I At (210) VIII 2 He Ne Ar Kr Xe Rn (222) Lanthanides Actinides 58 Ce Th Pr Pa Nd U Pm (145) 93 Np Sm Pu (244) 63 Eu Am (243) 64 Gd Cm (247) 65 Tb Bk (247) 66 Dy Cf (251) 67 Ho Es (252) 68 Er Fm (257) 69 Tm Md (258) 70 Yb No (259) 71 Lu Lr (26) Useful Equations and Constants: F = 96,485 C/mol e - ΔG o = -RT ln(k) R = J/K*mol = L*atm/K*mol ΔG o = ΔH o - TΔS o ΔS surr = -ΔH/T ΔS univ = ΔS sys + ΔS surr ΔG = ΔG o + RT ln(q) N A = x ε = ε o (RT/nF)lnQ ε = ε o (0.0591/n)logQ ΔG = -nfε ΔE = mc 2 c = 3.00 x 10 8 m/s 1 amu = x kg 1A = 1C/s 1 MeV = 1.60 x J ln[ A ] = kt + ln[ A Rate = k[a] ] 0 t 1 / 2 = k 11