Chemistry 30 Demos
Redox Reactions & Electrochemistry
IMPORTANT
ALWAYS follow proper safety precautions for ALL demonstrations!
A Dramatic Redox Reaction
CAUTION!
Do this in a fume hood. Be sure to use a suitable container!!!
Very exothermic.
PROCEDURE:
Place a small spoonful of potassium permanganate in a heat resistant container.
Pour a small amount of glycerin onto the pile (a dropperful or two)
The pile will produce smoke and fire in about 15 seconds (I've also had it sit for 15
minutes or more before it ignites)
THE REACTION:
14 KMnO4 (g) + 4 C3H5(OH)3 (l) → 7 K2CO3 (s) + 7 Mn2O2 (s) + 5 CO2 (g) + 16 H2O(l)
Reduction of Lead Oxide
PROCEDURE:
Place 20 g of lead(II) oxide, PbO, in a large pyrex test tube. Leave unstoppered
Heat over a bunsen burner for 30 minutes
Beads of lead will form on the inside of the test tube
THE REACTION:
2PbO → 2Pb + O2
Redox Reactions & Electrochemistry Demonstration Ideas
Silver - Copper Redox Reaction
This is a very simple demonstration to do if a solution of silver nitrate is kept on hand (store in a
brown bottle to keep light out). Within a few minutes the solid copper begins to darken, then turn
"fuzzy" as the silver comes out of solution to form a solid. The solution will begin to turn blue as
Cu2+ ions enter the solution.
This demonstration could be paired with the Zinc - Copper redox reaction to introduce the
activity series (Lesson 2.5).
PROCEDURE:
Place some clean copper wire or a copper strip in a small beaker or other container.
Add silver nitrate solution to cover (prepare by dissolving a few grams of AgNO3 in
about 100 mL of water). The concentration is not critical.
Within a few minutes solid silver will form on the metal surface and copper ions will
enter the solution, giving the solution a bluish hue.
THE REACTIONS: (the spectator ion, NO3-, has been removed)
Oxidation of Copper: Cu(s) → Cu2+(aq) + 2eReduction of Silver: Ag+(aq) + e- → Ag(s)
Net Reaction: Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)
Zinc - Copper Redox Reaction
Another very simple demonstration. If done with the silver-copper redox reaction demonstration,
the concept of an activity series (Lesson 2.5) can be introduced. When a zinc strip is placed in a
solution of copper(II) sulfate, the copper ions will be reduced with the zinc is oxidized. In the
silver-copper reaction, the copper was the metal undergoing oxidation. In the The solution will
begin to turn blue as Cu2+ ions enter the solution.
PROCEDURE:
Place a clean zinc strip in a small beaker or other container.
Add copper(II) sulfate solution to cover (prepare by dissolving a few grams of CuSO4 in
about 100 mL of water).
The zinc strip will become corroded as it undergoes oxidation; the blue colour of the
solution will fade as the copper ions become reduced and come out of solution.
THE REACTIONS: (the spectator ion, SO42-, has been removed)
Oxidation of Zinc: Zn(s) → Zn2+(aq) + 2eReduction of Copper: Cu2+(aq) + 2e-→ Cu (s)
Net Reaction: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu (s)
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Redox Reactions & Electrochemistry Demonstration Ideas
Synthesis of Zinc Iodide
Link to see images of this experiment: http://www.madison.k12.wi.us/east/science/zni2lab/zni2.htm
This redox reaction would be useful to demonstrate during the discussion of half-reactions. In
this synthesis reaction between zinc and iodine to form zinc iodide, zinc is oxidized and iodine is
reduced.
Pair this demonstration/lab with the Electrolysis of Zinc Iodide demonstration/lab. The ZnI2
synthesized in this demonstration will be decomposed.
These demonstrations could be done as a student lab rather than as a demonstration.
This demonstration could also be used to demonstrate the effect of a catalyst on reaction rate
(Unit 2, Lesson 4.4). This reaction will be very slow until catalyzed by water.
PROCEDURE:
Place about 0.2 g of powdered zinc in a watch glass. Fine powder works best, but course
ground works well, also. The quantities are not critical and may be approximated.
Weigh out 0.2 g of iodine crystals and add to the powdered zinc. If the iodine crystals are
large, grind them into a finer powder before mixing.
Mix the two solids together with a glass stirring rod. Although the reaction will begin upon
mixing, it will occur too slowly at room temperature to produce an immediate observable
change.
Place the watch glass on some white paper in a fume hood.
Add a ½ dropperful of water. Stir to mix well. The water will catalyze the reaction, allowing
it to occur at room temperature. Heat will be generated, causing some of the iodine to
vaporize, producing a violet "smoke".
The watch glass will now contain a gray slurry of unreacted zinc. The product of the
reaction, ZnI2, is water soluble so will not be visible yet.
To obtain the product, filter the contents of the watch glass. Place a clean beaker or
watchglass beneath a funnel fitted with filter paper, then pour the entire contents of the
watch glass onto the filter paper. Extra water may be added to completely rinse the watch
glass. The ZnI2 will be pass through the filter and collect in the beaker as part of the filtrate.
Discard the filter paper from the funnel and its contents. Pour the filtrate (the solution
collected in the beaker below the funnel) onto a clean watch glass.
Allow the water to evaporate from the watch glass. This may take a day or two. A white
solid, ZnI2, will remain.
THE REACTIONS:
Oxidation of Zinc: Zn(s) → Zn2+(aq) + 2eReduction of Iodine: I2 (s) + 2e- → 2 I-(aq)
Net Reaction: Zn(s) + I2 (s) → ZnI2 (s)
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Redox Reactions & Electrochemistry Demonstration Ideas
Electrolysis of Zinc Iodide
Link to see images of this experiment - http://www.madison.k12.wi.us/east/science/zni2lab/zni2.htm
In this demonstration, which could be done as a student lab, the product of the Synthesis of Zinc
Iodide demonstration is decomposed into it's elements through electrolysis.
PROCEDURE:
Obtain the solid ZnI2 that was prepared in the Synthesis of Zinc Iodide demonstration.
Place it on a watch glass if it is not already there.
Add a few drops of water to dissolve all of the white zinc iodide. Stir to make sure it all
dissolves.
You will need a battery (9-volt works well), two wire leads with alligator clips at both
ends, and to small pieces of copper wire (the electrodes), each a few cm long.
Assemble the apparatus - attach a wire lead to each post of the battery, and clamp the
small copper wire in the other ends of each wire lead. The copper wire electrodes will be
placed in the zinc iodide solution, keeping the two electrodes at opposite sides of the
watch glass. You may want to use clay or masking tape to help hold the electrodes in
place.
A gray coating of zinc will begin to form on the copper electrode that is attached to the
negative post of the battery as the zinc ions become reduced:
Zn2+(aq) + 2e- → Zn(s)
This electrode is the cathode, the site of reduction. The electrons required for this halfreaction are supplied by the battery.
At the electrode attached to the positive post of the battery iodine ions become oxidized
to form solid iodine crystals. These crystals will dissolve in the water producing an
amber, then red, colour. This electrode is the anode, the site of oxidation. The electrons
produced by this half-reaction return to the positive post of the battery.
2 I-(aq) → I2 (s) + 2eTHE REACTIONS:
Reduction of zinc ions: Zn2+(aq) + 2e- → Zn(s)
Oxidation of iodide ions: 2 I-(aq) → I2 (s) + 2e-
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