Chapter 21

Redox Review
(You will need to use page 712 in your textbook for this review game)
Multiple Choice:
1. What is the oxidation number of Cr in Cr2O3?
a. +6
d. +2
b. +3
e. –2
c. –3
2. What is the oxidation number of Cr in H2Cr2O7?
a. +6
d. +2
b. +3
e. –2
c. –3
3. What is the oxidation number of Cr in CrSO4?
a. +6
d. +2
b. +3
e. –6
c. –3
4. Investigate the following: 2Sr + O2  2SrO
Complete the following sentence: ______ is
reduced and ______ is oxidized.
a. Sr ; O
b. O ; Sr
c. O2 ; SrO
d. SrO2 ; Sr
e. Sr O2
5. In a reaction between sodium metal and zinc
chloride, ______ is reduced and ______ is
oxidized. (Hint: sodium has a lower
electronegativity than zinc).
a. Na ; Zn
b. Zn 2+ ; Na
c. Na ; Na
d. ZnCl2 ; Na
e. none of these are correct because this
reaction does not occur.
6. Calculate E0cell to determine whether the
following redox reaction is spontaneous as
Zn (s) + F2 (g)  2F1- (aq) + Zn2+ (aq)
a. No the reaction is not spontaneous
because the cell potential is 3.6278V
b. No the reaction is not spontaneous
because the cell potential is 1.5325V
c. Yes the reaction is spontaneous with a
cell potential of 3.6278V
d. Yes the reaction is spontaneous with a
cell potential of –5.6335V
e. No the reaction is not spontaneous with
a cell potential of –3.2531V
7. Which reaction would create a better battery?
reaction 1: 2Li (s) + Co2+ (aq)  2Li+ (aq) + Co (s)
reaction 2: 2I1- (aq) + K+ (aq)  I2 (g) + K (s)
a. reaction 1
b. reaction 2
c. neither reaction would create a
d. both are equally good batteries
8. The following equations are used to make an
electrolytic cell. Which reaction occurs at the
i. Br2 (l) + 2e-  2Br1- (aq)
ii. Na+ (aq) + e-  Na (s)
a. equation i
b. equation ii
c. neither – these reactions cannot create
an electrolytic cell.
9. The following equations are used in a galvanic
cell. Which reaction occurs at the anode?
i. Cd2+ (aq) + 2e-  Cd (s)
ii. MnO41- (aq) +8H+ (aq) + 5e-  Mn2+ (aq) +
4H2O (l)
a. equation i
b. equation ii
c. neither – these reactions cannot create a
galvanic cell.
10. In fuel cells, ____ act as fuel (Mark all that
a. Oxygen
c. zinc
b. Hydrogen
d. carbon dioxide
11. Which of the following statements is not true of
Redox reactions?
a. Oxidation must be accompanied by a
reduction reaction
b. Redox involves a loss and gain of
c. Involves a change in oxidation states of
the elements involved
d. Redox occurs in all reactions.
12. True or False? A lithium battery is used in cell
phones and electric cars since lithium has the
highest standard electrode potential of the
metallic elements.
a. true
b. false
13. The oxidation number of N in NH3 is –3. This
means (Mark all that apply)
a. that the nitrogen has a negative three
b. the hydrogen does not have any
electrons around it
c. the nitrogen is partially negative but
does not have a charge.
d. this is an ionic compound
e. –3 is a number we assign N so we can
track electrons.
15. What is the purpose of a salt bridge? (Mark all
that apply)
a) Allows the circuit to be complete in order
to allow electrons to travel.
b) Allows the oxidized metal to move to the
other side so the ions can become a solid.
c) Allows ions to move so the salt in the salt
bridge can be oxidized.
d) Allows ions to move to neutralize the
beakers so they do not get a build up of
14. What are the products for the following
unbalanced reaction? (Mark all that apply.)
NiCl2 + Na 
a) NaCl2
b) Ni+2
c) Ni
d) NaCl
e) This reaction does not occur
16. Which of the following are characteristics of
both electrolytic and voltaic cells? (Mark all
that apply)
a) an anode and cathode are present.
b) a battery is required to make the cell
work properly.
c) A salt bridge must be present to make the cell
d) A wire must connect the anode to the cathode
in order for the cell to work.
17. A cell is constructed by immersing a strip of lead in a 1.0M Pb(NO3)2 solution and a strip of silver in a 1.0M
AgNO3 solution. The circuit is completed by a wire and a salt bridge. As the cell operates, the strip of silver gains
mass (only silver), the strip of lead loses mass, and the concentration of lead ions increases in the solution around
the lead strip. Which of the following represents the reaction that occurs at the cathode in this cell?
a) Pb 2+  Pb + 2eb) Pb  Pb2+ + 2ec) Ag  Ag + + ed) Ag + + e-  Ag
18. Under standard conditions, what is the standard cell potential for the cell?
Cd|Cd2+ || Cu2+|Cu?
a. 0.74 V
b. -0.74 V
c. -0.06V
d. 0.06V
19. How many moles of electrons have been transferred between the species in the following reaction?
2Cr3+(aq) + 3Cu(s) → 2Cr(s) + 3Cu2+(aq)
a) 2
c) 4
b) 3
d) 6
Why do fuel cells not run down as batteries do?
Fuel is provided from an outside source
Fuel cells do not use chemical reactions
Fuel cells do not require an electrolyte
An example of electrolysis is (Mark all that Apply)
The flow of current from a primary battery
The charging of a secondary battery
Corrosion of an iron pipe
Addition of hydrogen gas to a fuel cell.
22. The electrolysis of an aqueous sodium chloride solution using inert electrodes produces gaseous chlorine at one
electrode. At the other electrode, gaseous hydrogen is produced, and the solution around the electrode becomes
basic. Which of the following equations is the correct equation for the cathode half-reaction in this electrolytic
a) 2Cl-  Cl2 + eb) 2H2O + 2e-  H2 + 2OHc) Cl2 + 2e-  2Cld) H2 + 2OH  2H2O + 2 e23. Electron flow is from the cathode to the anode in an electrolytic cell.
1. True
2. False
24. Nonmetals are usually good reducing agents for metals
a. True
b. False
Balancing Redox Reactions
1. Balance the following in basic solution:
NH3 (g) + O2 (g)  NO (g) + H2O (l)
2. Balance the following in acidic solution:
H6TeO6 (aq) + Br2 (g)  TeO2 (s) + BrO31- (aq)
Voltaic and Electrolytic Cells
1. Draw the voltaic cell composed of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell. Label the Zn, the Ni, the anode and the
cathode. Draw an arrow in the direction of the electron flow. Show the flow of positive and negative ions in the salt
bridge. Label the electrodes as positive or negative. Show the ions in solution.
c. Write the short hand notation for the reaction that occurs.
d. What is the maximum potential that can be achieved, using 1.0 molar solutions at 298K and 101 kPa?
2. In the following set-up, an aqueous solution of NiSO4 is electrolyzed. At the cathode, a whitish-gray solid substance
appears, and the pH is constant. At the anode, the pH drops, and bubbles of gas form. Label the drawing with the anode,
cathode, ion flow, electron flow and any gases and show equations for both the anode and cathode half-reactions.