Review Russo Ch. 9
1. Which of the following are redox reactions?
a) 2 Na + 2 H2O  2 NaOH + H2
b) MgBr2 + 2 NaF  MgF2 + 2 NaBr
c) 2 K + F2  2 KF
d) CH4 + 2 O2  CO2 + 2 H2O
2. Write any half-reactions that occur in 1a, 1b or 1c.
a) 2 Na  2 Na+ + 2 e- and 2 H+ + 2 e-  H2
c) 2K  2 K+ + 2 e- and F2 + 2e-  2 F3. Hydrogen gas burns very well in the presence of oxygen producing water vapor: 2 H2 + O2  2 H2O. In principal,
should it be possible to use this chemical reaction to produce electricity? Explain.
Yes – any time electrons are transferred, the electrons can potentially be captured & used to run a cell phone or
something, however technology may not be able to do this in every case, yet.
4. If you put a piece of iron in an aqueous solution of Cu2+ ions, the spontaneous redox reaction Fe + Cu2+  Fe2+ + Cu
will occur.
a) What is oxidized? Fe
b) What is reduced? Cu2+
c) What is the oxidizing agent Cu2+
d) What is the reducing agent Fe
e) Write the half-reaction occurring at the anode.
Fe  Fe2+ + 2 e-
f) Write the half-reaction occurring at the cathode.
Cu2+ + 2 e-  Cu
g) What will happen to the piece of iron over time? corrode
h) Do the electrons move from the oxidizing agent to the reducing agent or from the reducing agent to the oxidizing
agent?
5. Suppose you set up a battery with two metals, A and B, and solutions of their ions, A+ and B+. Metal B is more active
than metal A.
a) Write the spontaneous redox reaction for this situation. B + A+  A + B+
b) What is happening to the oxidizing agent? Getting reduced – gaining electrons
c) Describe the direction of electron flow. From B to A
d) Write the half-reaction that occurs at the cathode. A+ + e-  A
6. A zinc electrode and a copper electrode are used to make a battery.
a) Draw a battery similar to the ones you have done in class.
b) Indicate the direction of electron flow. From Zn to Cu
c) Add the labels anode and cathode to the drawing. Zn is anode
d) Write the spontaneous redox reaction (assume 2+ ions for each metal).
Zn + Cu2+  Zn2+ + Cu
7. Using the activity series, circle the spontaneous redox reactions in each set below.
a) 3K + Al3+  Al + 3 K+
or Al + 3K+  3K + Al3+
b) 3 Ag + Au3+  Au + 3 Ag+
or
Au + 3 Ag+
 3 Ag + Au3+
8. For each of the spontaneous reactions above, use a table of standard electrode potentials to calculate the voltage
obtainable. A) 1.27 v
b) 0.70 v
9. You are trapped on a desert island with plenty of water (both fresh and salt), a drinking glass, some wire, a radio, and
no batteries. You do have a tin cup, a tube of toothpaste containing stannous fluoride (SnF2, a source of Sn2+ ions), a
silver pendant and undeveloped black and white film (such film has silver bromide in it, a source of Ag+ ions).
a) How would you use the above materials to construct a battery? Show how with a diagram, including an arrow to
show which way the electrons flow. (You can make a salt bridge by soaking a sock in salt water and then dipping
one end in one cell and the other end in the other cell.)
b) Which metal would be eaten away? Explain. Tin bec. it is losing electrons
c) Which is the oxidizing agent? Ag+ ions
d) Write the half-reaction that will occur at the anode. Sn  Sn2+ + 2 e-
10. How can attaching a piece of Mg to the iron hull of a ship prevent the hull from rusting?
Reread the last section in chapter 9 for this information.
11. When you turn on an electrical appliance, are you consuming electrons? Explain.
No – electrons cannot be created or destroyed, just moved around from place to place.
12. A street vendor sells you a ring he claims is pure gold. However, when you place the ring in a solution of Cu2+ ions,
copper plates out on the ring.
a) How do you know the ring is a fake? Gold is lower on the activity series and should not react with Cu ions.
b) Could it be made of silver? No silver is also lower on the activity series than Cu
c) Was this a non-destruct test for the ring or is some of the ring now destroyed?
13. Use the table of standard electrode potentials to determine the voltage for batteries made using these metals and 1
M solutions of their ions at 298 K and 1 atm.
Reaction
Cell Potential (volts)
2.33v
a) I2/KI and F2/KF
b) Pb/PbCl2 and Na/NaCl
2.58v
c) Li/LiCl and Sn/SnCl4
3.05v
14. Identify one metal that could be used to reduce the cobalt out of a solution of cobalt ions.
Anything above Co on the activity series.