Chemistry 1312
Exam 4, Spring, 2004

I.   Multiple Choice (90 points)  Select the best response for each of the following and record on the scantron.  Do not erase; erasures may result in a misgrading of your response.

1.       An oxidation half-reaction
a.     occurs at the cathode of a galvanic cell                              d.    only b and c are correct
b.     shows an increase in oxidation state of an element       e.     a, b, and c are correct
c.     occurs at the (–) terminal of a galvanic cell

2.       In the redox reaction, 2 Bi(OH)₃  +  3 SnO₂^2- ® 2 Bi  +  3 H₂O  +  3 SnO₃^2-, identify the reducing agent.
a.     Bi(OH)₃                                                                                 d.    SnO₂^2-
b.     Bi                                                                                            e.     OH^-
c.     SnO₃^2-

3.       All of the following statements about galvanic cells are correct except
a.     The E°_cell is always positive                                             d.    The E_cell is independent upon ion concentrations
b.     The free energy change, DG°, is always negative      e.     Oxidation always occurs at the anode
c.     The cations in solution always migrate to the cathode

4.       In the cell diagram represented by Ag(s)|Ag⁺(aq)||Au³⁺(aq)|Au(s)
a.     Ag⁺ undergoes oxidation                                                d.    the concentration of Au³⁺ will decrease
b.     Au undergoes reduction                                                 e.     Au undergoes oxidation
c.     the anode half‑reaction is Ag⁺  +  e^-  ® Ag

5.       Identify the compound that is most likely a simple alkane.
a.     C₆H₁₄                                                                                     d.    C₆H₆
b.     C₃H₆                                                                                       e.     C₂H₄
c.     C₇H₁₄

6.                         CH₃                                                                             a.     1,2-dimethylhexane
                  |                                                                                   b.     2,3-dimethylbutane
CH₃–CH–CH–CH₃   is properly named as                              c.     2-methyl-3-methyl hexane
          |                                                                                           d.    2,2-dimethylbutane
          CH₃                                                                                     e.     1,4-dimethyl butane

7.       Which of the compounds is an ether?
a.     CH₃COCH₃                                                                          d.    CH₃OH
b.     CH₃OCH₃                                                                             e.     CH₃COOH
c.     CH₃CHO

8.       CH₃–CH₂–CH₂–CH₃ is called
a.     propane                                                                                d.    butene
b.     propene                                                                                e.     pentane
c.     butane

9.       Identify the compound that is classified as a carboxylic acid.
a.     CH₃CH₂CH₂OCH₃                                                             d.    CH₃CH₂COCH₃
b.     HCOOH                                                                               e.     CH₃CH₂CH₂CHO
c.     CH₃CH₂CH₂CH₂OH

10.    Identify the decay product having the greatest mass.
a.     alpha, a                                                                                d.    proton, p⁺
b.     beta, b                                                                                    e.     neutron, n
c.     gamma, g

11.    Determine the product, X, of the a,n transmutation reaction of Es(a, n)X
a.     ²⁵⁶Fm                                                                                      d.    ²⁵³Cf
b.     ²⁵⁵Lr                                                                                        e.     ²⁵⁷Md
c.     ²⁵⁶Md

12.    What is the daughter nucleus from the b-decay of Th?
a.     ²³⁵Th                                                                                       d.    ²³⁴Pa
b.     ²³³Pa                                                                                       e.     ²³⁴Ac
c.     ²³³Ac

13.    Complete the equation,  ®  Ca  +  _____
a.     alpha, a                                                                                d.    proton, p⁺
b.     beta, b                                                                                    e.     neutron, n
c.     gamma, g

14.    Identify the property that contributes least to the nuclear stability of an atom.
a.     a nucleus with a “magic number” of protons
b.     a nucleus with a “magic number” of neutrons
c.     a nucleus with a neutron to proton ratio greater than 1
d.    a nucleus with an even number of protons and an even number of neutrons
e.     a nucleus with an odd number of protons and an odd number of neutrons

15.    Determine “X” in the nuclear fission reaction,    ²³⁵U  +  ¹n  ®  ⁹⁴Kr  +  ¹³⁹Ba  +  3 X
a.     alpha, a                                                                                d.    proton, p⁺
b.     beta, b                                                                                    e.     neutron, n
c.     gamma, g

II.  Exercises (48 points).  The organization of all exercises must be shown clearly and legibly in order to receive any partial credit.  Answers without a logical problem setup will receive only 10% credit.

1.     (15 points)  The cell reaction and standard cell potential for a constructed galvanic cell is

         2 Cr  +  3 Co²⁺(1.50 M)  ®  2 Cr³⁺(1.0 x 10^-4 M)  +  3 Co, E°_cell = 0.46 V

a.     (10 pts)  Determine the actual cell potential for the galvanic cell.

E = 0.54 V

b.     (5 pts)  Explain why your answer is logical.

The cell potential should increase because of the low [Cr³⁺], increasing the “potential” of the cell reaction to go to the right.

2.     (10 points)  a.  (5 pts)  Write the complete nuclear equation for the alpha decay of californium-253, ²⁵³Cf

²⁵³Cf  ®  ²⁴⁹Cm  +  ⁴a

b.     (5 pts)  Write the complete nuclear equation for the transmutation of lead-208, ²⁰⁸Pb, in combining with nickel-62, ⁶²Ni, to form the product nucleus with the emission of a neutron, ¹n

²⁰⁸Pb +  ⁶²Ni  ® ²⁶⁹Ds  +  ¹n

3.     (23 points)  a.  (5 pts)  Write the cell diagram for a galvanic cell constructed from the following two half‑cells:
Sn⁴⁺  +  2 e^-  ®  Sn²⁺                           E° = +0.15 V
Ga³⁺  +  3 e^-  ®  Ga                            E° = –0.55 V

Ga|Ga³⁺||Sn⁴⁺,Sn²⁺|Pt or C(gr)

b.     (5 pts)  Write the cell reaction for the galvanic cell.

3 Sn^{4+  +}  2 Ga  ®  3 Sn²⁺  +  2 Ga³⁺

c.     (8 pts)  Calculate the equilibrium constant for the cell reaction.

K = 8.8 x 10⁷⁰

d.    (5 pts)  Calculate the standard free energy change, DG°, for the cell.

DG°  = ­405 kJ