Exam 4A, Spring 2005

1. Complete and balance the following reactions:

a. Mn(OH)₂(s) + H₃PO₄(aq)

b. Na₂CO₃(aq) + Fe(NO₃)₃(aq)

c. As₂S₃(s) + H₂O₂(aq) → H₃AsO₄(aq) + SO₄^2–(aq)

d. XeF₆(s) + OH^–(aq) → O₂(g) + XeO₆^4–(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 acidic solution? Show chemical equations to justify your answer.

4. Consider the electrochemical cell shown below.

Pt | Br^–(aq) | BrO₃^–(aq) | pH = 14 || O₂(g) | pH = 14 | 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 10 in each half-cell, would the standard potential increase, decrease, or stay the same? Why?

Answers