Oxidation-Reduction And The Activity Series
Objectives
You should be able to visually determine when an oxidation-reduction reaction has occurred and
rank oxidizing/reducing agents from strongest to weakest based on experimental evidence. You
should also be able to write half-reactions for the reactions you perform.
Introduction
In this course we have studied reactions that fall into many different categories, one of which was
redox reactions. In a redox reaction, electrons are transferred from one chemical species to
another. The oxidation number of one atom in the reaction increases while the oxidation number
of another atoms in the reaction decreases. In the reaction of Zn with Pb(NO 302, zinc is oxidized to
Zn2+ and Pb2+ is reduced to elemental lead, with an oxidation number of zero.
Zn(s) + Pb(NO3)2(aq)  Pb(s) + Zn(NO3)2(aq)
eq. 1
The oxidizing agent is lead and the reducing agent is zinc. Zinc is the more powerful reducing
agent since the reaction occurs in the direction written. If combining zinc metal and lead nitrate
did not lead to a reaction, then lead would have been the more powerful reducing agen.
Fluorine is reduced to fluoride ions in the reaction below.
F2(g) + 2Br -(aq)  2F – (aq) + Br2(l)
eq. 2
Fluorine is the oxidizing agent and is a more powerful oxidizing agent than Br 2.
In the first part of today’s experiment, we will rank Fe (steel wool), Cu, H +, Mg and Zn from strongest
to weakest reducing agents. If Cu metal reduced the Zn 2+ ion in solution to zinc metal, then copper
metal is a stronger reducing agent than zinc metal. In the second part of the experiment, you will
determine the oxidizing abilities of Br2, I2 and Fe3+.
Experiment
Part A: Metals as Reducing Agents
Work in Partners. Make three tables to record the data from the three short experiments in this part
of today’s laboratory experiment.
Obtain four clean test tubes. Put a 2 cm piece of copper wire in one tube, a 2 cm piece of
magnesium ribbon in the second tube (rub the magnesium ribbon with and paper briefly before
placing it in the tube), put a 2 cm piece of zinc wire in the third tube, and put a small bit of steel
wool in the last test tube.
To each test tube add 5 mL of 0.1 M CuSO4 and note any reaction that occurs in the three minute
period. Signs of a reaction could include appearance of bubbles, temperature of the contents of
the test tube increasing, decrease in blue color of copper solution, or appearance of solid metal
shavings in or on the metal.
Dump the contents of the test tubes in the waste container provided. Retain the pieces of metal
and carefully rinse them with deionized water. Rinse the test tubes thoroughly.
Place each piece of metal back into a test tube and add 5 mL of 3M H 2SO4. Watch carefully for
any reaction that occurs in the first three minutes. Hold a burning splint over any test tube in which
bubbling occurs. What is the gas?
Clean the metals and test tubes as before and repeat the experiment with 0.1 M ZnSO 4.
Based on your observations, rank the four metals and H+ from strongest reducing agent to weakest
reducing agent. If an observable reaction occurred, complete and balance an equation for the
reaction. (Fe is oxidized to Fe2+, Cu is oxidized to Cu2+-, and Zn is oxidized to Zn2+.) For each
reaction, circle the oxidizing agent.
Part B: Halogens and Iron(III) Ions as Oxidizing Agents
Work in partners for this experiment. Make a table to record your results.
Obtain three clean test tubes and place about 5 mL of 0.1 M NaBr in the first tube, 5 mL of 0.1 M
NaCl in the second tube, and 0.1 M NaI in the third tube. Add 5 mL of 0.1 M FeCl 3 to each tube
and note any reaction in the first three minutes. The iron solution will have a less intense color
immediately because it is being diluted and is not an indication that a chemical reaction has
occurred. Was the iron(III) ion able to oxidize any of the halides?
Based on your observations, rank Br2, Cl2, I2, and Fe3+ from strongest to weakest oxidizing agent (as
best you can).
If an observable reaction occurred, complete and balance an equation for the reaction. (Fe 3+ is
reduced to Fe2+ when a reaction occurs.) For each reaction, circle the reducing agent.
Suggest an experiment or two that would resolve any uncertainty in the oxidizing agent’s lists. Be
specific about what chemical species you would combine.
Part C: Check-Out
Check out of your laboratory drawer. Remove all of the contents of the drawer. Wash the inside of
the drawer thoroughly. Place new papers towels in the bottom of the drawer and return ONLY
those items on the check-out sheet to the drawer. If you have excess glassware, place it in the
large wash tub in the laboratory room. If you are missing equipment, search the washtub for
replacement pieces. When your drawer is in very good condition, ask the laboratory instructor or
the teaching assistant to sign your check-out sheet. A completed check-out sheet is a major
portion of this week’s laboratory grade.