Stoichiometry and Free Energy Worksheet
1.
How many coulombs, q, are required to deposit 0.587 g of Ni from a solution of Ni2+ ?
Ni2+ + 2e¯ 
Ni
m = 0.587 g
M = 58.69 g/mol
q
then q  n e - x F
F
n e- 
1 mol Ni
2 mol e 9.65 x 10 4 C
q  0.587 g x
x
x
58.69 g 1 mol Cu 2 
mol e  1930 C  1.93 x 10 3 C
2.
Three electrolysis cells are connected in series. They contain, respectively, solutions of copper (II)
nitrate, silver nitrate, and chromium (III) sulfate. If 1.00 g of copper is electrochemically deposited in the
first cell, calculate the mass of silver and chromium deposited in the other cells.
1)
Cu2+ + 2e¯ 
Cu
m = 1.00 g
M = 63.55 g/mol
1 mol Cu 2 mol en e - (Cu )  1.00 g x
x
 0.0315 mol
63.55 g 1 mol Cu
2)
Ag+
+ e¯

n = 0.315 mol
Ag
m=?
M = 107.87 g/mol
m Ag  0.0315 mol e - x
3)
Cr3+ + 3e¯

n = 0.315 mol
1 mol Ag
1 mol e-
x
107.87 g
 3.40 g
1 mol Ag
Cr
m=?
M = 52.00 g/mol
mCr  0.0315 mol e- x
1 mol Cr 52.00 g
x
 0.546 g
1
mol
Cr
3 mol e
3.
A constant current of 3.7 milliampere is passed through molten sodium chloride for 9.0 minutes. The
sodium produced is allowed to react with water (500 mL). What is the pH of the resulting solution?
Na+
e¯

I = 3.7 mA
t = 9.0 min
= 540 s
+
Na
n=?
3.7 x 10 -3 C
mol e1 mol Na
n Na 
x 540 s x
x
s
9.65 x 10 4 C
1 mol e 2.1 x 10 -5 mol
2 Na
+
2 H2O
n = 2.1 x 10-5 mol

2 NaOH
+
H2
C= ?
V = 0.500L
C NaOH  2.1 x 10 -5 mol x
2 mol NaOH
1
x
2 mol Na
0.500 L
 4.2 x 10 -5 M
pH  14  log (4.2 x 10 -5 )
 9.62
4. Given these half-reactions and their standard reduction potentials.
2 ClO4- + 12 H+ + 10 e-  Cl2 + 6 H2O
S2O82- + 2 e-  2 SO42Calculate:
(a) Complete the REDOX reaction.
an (ox):
5 x cat (red):
Eo (ClO4-) = + 1.47 V
Eo (S2O82-) = + 2.01 V
Cl2 + 6 H2O  2 ClO4- + 12 H+ + 10 e5 S2O82- + 10 e-  10 SO42-
Eo = - 1.47 V
Eo = + 2.01 V
5 S2O82- + Cl2 + 6 H2O  10 SO42- + 2 ClO4- + 12 H+
(b) Eocell = + 2.01 - 1.47 V = + 0.54 V
(b) ΔGo for the cell reaction
G o = - n F E ocell
9.65 x 104 C  0.54 J
 - 10 mol e x
x
 - 520 000 J  - 520 kJ
C
mol e-
(c) Keq for the cell reaction.
- 520 000 J  mol -1
ln K eq  G 
 - 210
RT 8.314 J  mol -1  K -1 x 298 K
(- G )
K eq  e RT  e(-(-210))  1.6 x 1091
5. The system 2 AgI + Sn  Sn2+ + 2 Ag + I- has a calculated Eocell = -0.015 V. What is the
value of Keq for this system?
ocell 2 mol e- x 9.65 x 104 C x - 0.015 J  C-1
nFE
ln K eq 

 - 1.2
RT
1
1
8.314 J  mol  K x 298 K
K eq  e
cell )
( nFERT
 e(-1.2)  0.31
6. Calculate ΔGo for the following reaction, given that its standard cell potential is 0.320 V at 25oC.
NiO2 + 2 Cl- + 4 H+  Cl2 + Ni2+ + 2 H2O
G o = - n F E ocell
9.65 x 104 C  0.320 J
 - 2 mol e x
x
 - 67 600 J  - 67.6 kJ
C
mol e-