The REDOX Packet
1. Cr2O7-2 + 6I- + 14H+  2Cr+3 + 3I2 + 7H2O
Which of the following statements about the reaction given above is NOT true?
(A)
The oxidation number of chromium changes from +6 to +3
(B)
The oxidation number of iodine changes from -1 to 0
(C)
The oxidation number of hydrogen changes from +1 to 0
(D)
The oxidation number of oxygen remains the same
(E)
The reaction takes place in acidic solution
2. In which of
(A)
(B)
(C)
(D)
(E)
the following molecules does hydrogen have an oxidation state of -1?
H2O
NH3
CaH2
CH4
H2
3. MnO4-(aq) + SO3-2(aq)  MnO4-2(aq) + SO4-2(aq)
In the above equation, which species contains the element that is being reduced?
(A)
MnO4-(aq)
(B)
SO3-2(aq)
(C)
MnO4-2(aq)
(D)
SO4-2(aq)
(E)
Oxidation numbers remain constant. This is not a redox reaction.
4. The oxidation number of V in VOCl3 is
(A)
-6
(B)
0
(C)
+5
(D)
+6
(E)
+8
5. Al+3 + 3e-  Al(s) Eo = -1.66V
Cr+3 + 3e-  Cr(s) Eo = -0.74V
The standard reduction potentials for two half-reactions are shown above. Which of the
statements listed below will be true for the following reaction taking place under standard
conditions?
Al(s) + Cr+3  Al+3 + Cr(s)
(A)
Eo = 2.40V, and the reaction is not spontaneous
(B)
Eo = 0.92V, and the reaction is spontaneous
(C)
Eo = -0.92V, and the reaction is not spontaneous
(D)
Eo = -0.92V, and the reaction is spontaneous
(E)
Eo = -2.40V, and the reaction is not spontaneous
6. Cu+2 + 2e-  Cu
Fe+2 + 2e-  Fe
Eo =+0.3V
Eo =-0.4V
Based on the reduction potentials given above, what is the reaction potential for the
following reaction?
Fe+2 + Cu  Fe + Cu+2
(A)
-0.7V
(B)
-0.1V
(C)
+0.1V
(D)
+0.7V
(E)
+1.4V
7. Cu+2 + 2e-  Cu
Zn+2 + 2e-  Zn
Mn+2 + 2e-  Mn
Eo = +0.3V
Eo = -0.8V
Eo = -1.2 V
Based on the reduction potentials given above, which of the following reactions will occur
spontaneously?
(A)
Mn+2 + Cu  Mn + Cu+2
(B)
Mn+2 + Zn  Mn + Zn+2
(C)
Zn+2 + Cu  Zn + Cu+2
(D)
Zn+2 + Mn  Zn + Mn+2
(E)
Cu+2 + Zn+2  Cu + Zn
8. When solid iron is brought into contact with water and oxygen, it undergoes the following
half-reaction:
Fe(s)  Fe+2 + 2eThis half-reaction is instrumental in the corrosion of iron. When iron is coated with solid
zinc, the half-reaction above is impeded, even if the zinc coating is incomplete. This is
most likely because
(A)
Zn(s) is more easily reduced than Fe(s)
(B)
Zn(s) is more easily oxidized than Fe(s)
(C)
Zn+2(aq) is more easily reduced than Fe(s)
(D)
Zn+2(aq) is more easily oxidized than Fe(s)
(E)
Zn(s) is more easily reduced than Fe+2(aq)
9. Which of the following is true about the oxidation-reduction reaction that takes place in a
galvanic cell under standard conditions?
(A)
Go and Eo are positive, and Keq is greater than 1
(B)
Go is negative, Eo is positive, and Keq is greater than 1
(C)
Go is positive, Eo is negative, and Keq is less than 1
(D)
Go and Eo are negative, and Keq is greater than 1
(E)
Go and Eo are negative, and Keq is less than 1
Free Response Questions
1. An electrochemical cell was created by placing a zinc electrode in a 1.00-molar
solution of ZnSO4 and placing a copper electrode in a 1.00-molar solution of
CuSO4. The two compartments were connected by a salt bridge, and the following
reaction occurred at 25oC:
Zn(s) + Cu+2  Zn+2 + Cu(s)
(a)
What is the standard potential for the cell?
(b)
What is the value of Go for the cell?
(c)
What is the value of Keq for the reaction?
(d)
At a certain point in the process of the reaction, [Cu+2] drops to 0.10molar and [Zn+2] increases to 1.9-molar. What is the cell potential at
this point?
2. Use the principles of electrochemistry to answer each of the following:
(a)
Explain why a salt bridge connecting the two compartments of a
galvanic cell is necessary for the operation of the cell.
(b)
Ag+ + Sn(s)  Ag(s) + Sn+2
(i)
Give the standard cell potential for the reaction above
(ii)
What happens to the cell potential in (i) when [Ag+] is
increased?
(iii)
What happens to the cell potential when the amount of Sn(s)
in the cell is increased?
3. M(s) + Cd+2  M+ + Cd(s)
The reaction above proceeds spontaneously at 25oC in an electrochemical cell.
(a)
The reduction potential for M(s) must be less than a certain value.
What is that value?
(b)
Write the two half-reactions, and identify which takes place at the
anode and which takes place at the cathode
(c)
Describe the changes that occur in the quantities below as the reaction
proceeds in the forward direction.
(i)
[M+]
(ii)
Ecell
(iii)
G