Chapter 10 Laboratory: Reduction-Oxidation (Redox) Reactions 183LABORATORY 1 0.1:
REdUCTIoN of CoppER oRE To CoppER mETAL
It may surprise you to learn that at least
one redox reaction was discovered and used
thousands of years ago. Like many discoveries
in chemistry, this one was purely accidental.
We can speculate about what happened. One
evening long ago, some of our remote ancestors
gathered around a fire built in a circle of stones.
Those stones happened to be chunks of a
copper-bearing ore, probably copper carbonate.
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ balance and weighing paper£ ring stand£ support ring£ clay triangle£ crucible and lid£ crucible tongs£ gas burner£ copper carbonate (~5 g)£ activated charcoal (~3 g)All of the required elements were present. The copper ore
provided the copper ions. The charred wood provided the carbon
in the form of charcoal. The fire provided the heat needed to
initiate and sustain the reaction. Here’s what happened:
2 CuCo 3 (s) + C(s) → 2 Cu(s) + 3 Co 2 (g)
or, showing the oxidation states:
2 Cu2+[C4+(o2– 3 )]2– + C^0 (s) → 2 Cu^0 (s) + 3 C4+(o2– 2 )
As the fire burned during the night, some of the copper ore
and charcoal disappeared and, as if by magic, were replaced
by a shiny puddle of metallic copper. Chances are that this had
happened many times before and no one thought much about it,
if they even noticed. But this time someone did notice and started
wondering. What was this shiny new substance? Could it be used
for anything? Can we get more of it just by heating rocks?
wHATB A oUT fE4+ N EA df+?
It might seem that an Fe3+ ion could lose one more
electron to produce an Fe4+ ion. That doesn’t happen,
because of the configuration of iron’s electron shell. Only
tightly bound electrons remain when iron is in the +3 state.
Similarly, it might seem that Fe^0 could lose one electron
(or Fe2+ gain one electron) to form Fe+. That doesn’t
happen, because the electron shell configuration of Fe+
is unstable. Any Fe+ ions that fleetingly form during an
oxidation-reduction reaction immediately shed an electron
to form Fe2+ ions or grab an electron to form Fe^0.kEENGpI oxIdATIoN ANd REdUCTIoN STRAIGHT
Many beginning chemists have trouble remembering
whether oxidation means gaining or losing an electron.
Generations of chemists have kept this straight using the
mnemonic LEO the lion says GER, which you can expand
to Lose Electron = Oxidation and Gain Electron
= Reduction.At the time, metallic copper was known, but the only source was
small, rare deposits of natural metallic copper. The discovery
that copper metal could be obtained by heating copper ore in
conjunction with charcoal, a process called smelting, marked the
end of the Stone Age.In this lab, we’ll recreate that first accidental smelting of copper
ore to copper metal.