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Exam 4B
Spring 2005


Possibly useful information:

Eocell = Eored + Eoox

Go = –nFEo

nF = At

 

Standard Reduction Potentials

Eo (V)

2 BrO3(aq) + 12 H+(aq) + 10 eBr2(l) + 6 H2O(l)

1.478

BrO3(aq) + 6 H+(aq) + 6 eBr(aq) + 3 H2O(l)

1.409

O2(g) + 4 H+(aq) + 4 e2 H2O(l)

1.229

Br2(l) + 2 e2 Br(aq)

1.065

BrO(aq) + H2O(l) + 2 eBr(aq) + 2 OH(aq)

0.766

BrO3(aq) + 3 H2O(l) + 6 eBr(aq) + 6 OH(aq)

0.584

BrO(aq) + 2 H2O(l) + 2 eBr2(l) + 4 OH(aq)

0.455

O2(g) + 2 H2O(l) + 4 e4 OH(aq)

0.401


1. Complete and balance the following reactions:

a. Ni(OH)2(s) + H3PO4(aq)

b. K2CO3(aq) + Co(NO3)3(aq)

c. As2S3(s) + H2O2(aq)H3AsO4(aq) + SO42–(aq)

d. XeF6(s) + OH(aq)O2(g) + XeO64–(aq) + F(aq) + Xe(g)

e. The disproportionation of chlorate ion into chlorite ion and perchlorate ion in basic solution.

2. Identify the oxidation number of:

a. V in (VO)(SO4)

b. Fe in Fe3O4

3. Can oxygen gas be used to oxidize bromide ion in basic solution? Show chemical equations to justify your answer.

4. Consider the electrochemical cell shown below.

Pt | Br(aq) | BrO3(aq) | pH = 1 || O2(g) | pH = 1 | Pt

a. Write the oxidation half-reaction.

b. Write the reduction half-reaction.

c. Write the net reaction.

d. Calculate the cell potential at standard conditions.

e. Is the reaction spontaneous, nonspontaneous, or at equilibrium? Why?

f. If you were to calculate the thermodynamic equilibrium constant for the reaction, what value would you use for n?

g. Write the expression for the reaction quotient for the cell.

h. If the pH were to be changed to 5 in each half-cell, would the standard potential increase, decrease, or stay the same? Why?