AP Chemistry Review Sheet
Electrochemistry
Chapter 17
BASIC TERMS:
CELLS:
oxidation, reduction, agents,
cathode, anode, E°red, E°ox, E°tot
Voltaic or galvanic <energy producing> E°tot +
Electrolytic <energy using> E°tot -
DIAGRAM CELL & NOTATION: flow of e- and ions
What happens at the anode-cathode
USING E°red TABLE: Find E°tot - standard conditions
Strengths of agents, what reaction occur
EQUATIONS:
ΔG°(kJ) = -96.5 n E°tot
ln K = n E°tot @ 25 °C
0.0257
CONC. EFFECT ON VOLTAGE: LeChatelier’s (Qualitative)
Nernst (Quantitative)
Solve for E or con.
COUNT ELECTRONS:1 coulomb = 1 amp•sec
1 mole e- = 96,485 C
Use reaction to find amount plated
(mole ratio)
(Over for practice problems)
PRACTICE:
• An electrolytic cell contains a solution of Cr(NO3)3. Assume that chromium metal
plates out at one electrode and oxygen gas is evolved at the other electrode.
a. Write the anode half-reaction, the cathode half-reaction, and the overall reaction
for the cell.
b. How long will it take to deposit 15.0 g of chromium metal, using a current of 4.50 A?
c. A current of 4.50 A is passed through the cell for 30.0 min. If we start out with
250 mL of 1.00 M Cr(NO3)3, what is the concentration of Cr3+ after electrolysis? The
pH of the solution? Assume 100% current efficiency and no change in volume during
electrolysis.
A voltaic cell consists of two half-cells, one of which contains a Pt electrode
surrounded by Cr3+ and Cr2O72- ions. The other half-cell contains a Pt electrode
surrounded by Mn2+ ions and MnO2 (s). Assume the cell reaction, which produces a
positive voltage, involves both Cr3+ and Mn2+ ions.
d.
e.
f.
g.
Write the anode half rxn, the cathode half-rxn, and the overall equation for the cell.
Write the cell description in abbreviated notation.
Calculate E°tot for the cell
For the redox reaction in (d), calculate K and _G°.
h. Calculate the voltage of the cell when all ionic species except H+ have a
concentration of 0.300 M and the solution has a pH of 3.5.
ANSWERS:
a. anode: Cr3+ (aq) + 3 e - <==> Cr (s)
cathode: 2 H2O2 <==> 4 H+ (aq) + O2 (g) + 4 e overall: 4 Cr3+ (aq) + 6 H2O <==> 4 Cr (s) + 12 H+ (aq) + 3 O2 (g)
b. 5.15 h
c. 0.888 M Cr(NO3) 3; pH = 0.47
d.
e.
f.
g.
h.
anode: Mn2+ (aq) + 2 H2O <==> MnO2 (s) + 4 H+ (aq) + 2 e cathode: Cr2O7 2- (aq) + 14 H+ (aq) + 6 e - <==> 2 Cr3+ (aq) + 7 H2O
overall: 3 Mn2+ (aq) + Cr2O7 2- (aq) + 2 H+ (aq) <==> 2 Cr3+ (aq) + 3 MnO2 (s) + H2O
(Pt)Mn2+/MnO2||(Pt) Cr2O7 2-/Cr3+
0.10 V
K = 1.4 x 1010; G° = - 58 kJ
0.02 V