Cliffs AP Chemistry, 3rd Edition

Experiment 20: Determination of Electrochemical

Series

and

Experiment 21: Measurements Using

Electrochemical Cells and Electroplating

Background:When electrons are transferred during the course of a reaction, the reaction is
called an oxidation-reduction reaction, or redox reaction for short. The reactant that donates
electrons is said to be oxidized and the species that gains electrons is said to be reduced (OIL
RIG- Oxidation is Losing, Reduction is Gaining). To illustrate oxidation, examine the half-re-
action

ox: Cu()s"Cu()^2 aq++=- 2034 e- Eoox. V

Here you can see that the reactant, solid copper, has a 0 oxidation state. It changes to the cop-
per (II) ion by losing 2 electrons and is said to be oxidized. The mass of the solid copper will
decrease as the reaction proceeds.

In the reduction reaction

red: Ag()+-aq+=e "Ag()s Eredo 0 799. V

the Ag+ion is reduced to the silver atom. If the summation of the voltages is positive, the reac-
tion is said to be spontaneous and work can be done. If the summation of the voltages is nega-
tive, then work must be done on the system, through the use of a battery, to cause the reaction
to occur. In the example above, if a copper wire was placed in a solution of silver nitrate, the
copper wire would oxidize to Cu2+ions and silver ions in solution would be reduced and begin
to collect on the copper wire as silver atoms.

In Part I of this experiment, different metals will be added to solutions of different aqueous
ions to determine whether a spontaneous redox reaction occurs. Also tested will be the colors
of three halogens and their corresponding halide ion in mineral oil. Halogens such as Br2(aq),
Cl 2 (aq) and I 2 (aq) dissolve in nonpolar solvents such as mineral oil to give a characteristic
color. And finally in Part I, various combinations of these halogens and halides will be mixed
and observations recorded.

In Part II, cells will be constructed to determine the relative magnitudes of E and E^0 , the deter-
mination of a solubility product and a formation constant. In both parts, the relative activity of
elements will be determined.

Laboratory Experiments