Chapter 20 – Electrochemistry Practice
Name: _______________________________________________ Period:____________
1. The following reaction takes place in an electrochemical cell:
Cu2 + (aq) + Zn(s)  Cu(s) + Zn2 + (aq)
a. Which electrode is the anode?
b. Which electrode is the cathode?
c. Write the cell notation for this system.
d. Write equations for the half-reactions that occur at each electrode and label each reaction.
2. Below is a diagram of an electrochemical cell.
a.
Write the anode half-reaction.
b.
Write the cathode half-reaction.
c.
Write the balanced overall cell reaction.
d. Do electrons within the electrochemical cell travel through the voltmeter in a
clockwise or a counterclockwise direction, as represented in the diagram?
e. In what direction do anions pass through the porous membrane, as represented in
the diagram?
Example Problem 1
Calculating Cell Potential
The half-cells of a voltaic cell are represented by these two reduction half-reactions.
Cr2+(aq) + 2e-  Cr(s)
Al3+(aq) + 3e-  Al(s)
Determine the overall cell reaction and the standard cell potential. Express the reaction using cell notation.
3.For each pair of half-reactions, write the balanced equation for the overall cell reaction, calculate the standard cell potential,
and express the reaction using cell notation. Use E 0 values from Table 1 in your notes.
a. Mg2+(aq) + 2e-  Mg(s)
Pb2+(aq) + 2e-  Pb(s)
c. Cr3+(aq) + 3e-  Cr(s)
2H+(aq) + 2e-  H2(g)
b. Cu2+(aq) + e-  Cu+(s)
Cd2+(aq) + 2e-  Cd(s)
Example Problem 2
Predicting the Spontaneity of a Reaction
Predict whether the following redox reaction will occur spontaneously. Use E 0 values from Table 1 in your notes.
2Cr3+(aq) + 3Sn2+(aq)  2Cr(s) + 3Sn4+(aq)
4.Calculate the cell potential to determine if each of these redox reactions is spontaneous. The half-reactions can be found in
Table 1.
a. 2Ag+(aq) + Co(s)  Co2+(aq) + 2Ag(s)
b. Cu(s) + Cu2+(aq)  2Cu+(aq)
c. 2Br2(l) + 2H2O(l)  4H+(aq) + 4Br- (aq) + O2(g)
d. 5Fe2+(aq) + MnO4- (aq) + 8H+(aq)  5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
Use Table 1 from your notes to find E0 for the following voltaic cells:
5)Al(s) | Al3 + (aq) || Cd2 + (aq) | Cd(s)
6) Fe(s) | Fe2 + (aq) || Pb2 + (aq) | Pb(s)
7) 6I– (aq) +2Au3 + (aq)  3I2(s) +2Au(s)
8) A voltmeter connected to a copper-silver voltaic cell reads +0.46 V. The silver is then replaced with metal X and its 2+ ion.
A new voltage reading shows that the direction of the current has reversed, and the voltmeter reads +0.74 V. Use data
from Table 1 from your notes to answer.
a) Calculate the reduction potential of metal X.
b) Predict the identity of metal X.
9.Calculate the standard cell potentials of voltaic cells that contain the following pairs of half-cells. Use E 0 values from Table 1.
a. iron in a solution of Fe2+ ions; silver in a solution of Ag+ ions
b. chlorine in a solution of Cl- ions; zinc in a solution of Zn2+ ions
Table 1 – Standard Reduction Potentials
Table 2
INCREASING ACTIVITY
Reducing
agents
Li
K
Ca
Na
Mg
Al
Zn
Cr
Fe
Ni
Sn
Pb
H2
H2S
Cu
IMnO42Fe2+
Hg
Ag
NO21BrSO2
Cr3+
ClMn2+
F-
Oxidizing
agents
Li+
K+
Ca2+
Na+
Mg2+
Al3+
Zn2+
Cr3+
Fe2+
Ni2+
Sn2+
Pb2+
H3O+
S
Cu2+
I2
MnO4Fe3+
Hg22+
Ag+
NO31Br2
H2SO4
Cr2O72Cl2
MnO41F2
INCREASING ACTIVITY
RELATIVE STRENGTH
OF OXIDIZING AND
REDUCING AGENTS