How are Chemistry and Electricity Related?
AP Chem Unit 16: Practice Problems
1
Practice Problem #1: Potassium dichromate (K2Cr2O7) is a bright orange compound that can
be reduced to a blue-violet solution of Cr3+ ions. Under certain conditions, K2Cr2O7 reacts with
ethyl alcohol (C2H5OH) as follows:
Balance this equation using the half-reaction method.
Practice Problem #2: Silver is sometimes found in nature as large nuggets; more often it is
found mixed with other metals and their ores. An aqueous solution containing cyanide ion is
often used to extract the silver using the following reaction that occurs in basic solution:
Balance this equation using the half-reaction method.
2
Practice Problem #3a: Consider a galvanic cell based on the reaction:
Give the balanced cell reaction and calculate Eo for the cell.
Practice Problem #3b: Consider a galvanic cell based on the reaction:
Give the balanced cell reaction and calculate Eo for the cell.
Practice Problem #4: Describe completely the galvanic cell based on the following half
reactions under standard conditions: Eo=0.80V and Eo=0.77V
3
Practice Problem #5: Using cell potential data, calculate the ΔGo for the reaction:
2+
2+
Cu(aq)
+ Fe(s) ® Cu(s) + Fe(aq)
Is this reaction spontaneous? (remember: -ΔG is spontaneous)
Practice Problem #6: Using cell potential data, predict whether 1M HNO3 will dissolve gold
metal to form a 1M Au3+ solution.
4
Practice Problem #7: For the cell reaction:
E= 0.48V Predict whether Ecell is larger or smaller than Eocell for the following cases.
a. [A3+]=2.0M, [Mn2+]= 1.0 M
b. [A3+]=1.0M, [Mn2+]= 3.0 M
Practice Problem #8: Determine the direction of electron flow and designate the anode and
cathode for the cell:
5
Practice Problem #9: Calculate the potential and describe the cell based on the following halfreactions: Eo=1.00V and Eo = -0.76V
T=25°C, [VO2+] = 2.0M,
[H+]=0.50M,
[VO2+] = 1.0x10-2M. [Zn2+]= 1.0x10-1M
Practice Problem #10: For the oxidation-reduction reaction,
22+
3+
2S4O6(aq)
+ Cr(aq)
® Cr(aq)
+ S2O3(aq)
The half reactions are: E=0.17V and
E=-0.50V
Balance the redox reaction, and calculate Eo and K (at 25°C)
6
Practice Problem #11: How long must a current of 5.00 A be applied of Ag+ to produce 10.5 g of
silver metal.
Practice Problem #12: An acidic solution contains the ions Ce4+, VO2+, and Fe3+. Using the cell
potential table, give the order of oxidizing ability of these species and predict which one will be
reduced at the cathode of an electrolytic cell at the lowest voltage.
7