Video Transcript
Which metal could not be used for
electroplating through the use of an aqueous solution? (A) Gold, (B) silver, (C) chromium,
(D) sodium, or (E) copper.
Electroplating requires
electrolysis. An electrolysis reaction is a
reaction that uses an electrical current that is passed through a solution that
contains ions which cause the substances inside to decompose or break apart. Electroplating is a type of
electrolysis reaction that coats one type of metal with another through electrolytic
deposition or using an electrolytic reaction to deposit metal ions onto the surface
of another metal.
The setup for these reactions
involves a power source, an electrolytic cell, a negatively charged cathode
electrode, a positively charged anode electrode, and an electrolyte solution. A liquid electrolyte solution
contains the ions that are to be manipulated, for example, the metal ions that will
be used to coat the other metal. A metal’s reactivity is an
important consideration when choosing the metal that you can plate with. A metal can typically only be
electroplated if the metal with which it will be electroplated is more reactive than
itself.
So, to answer our question, we need
to know the reactivity of the metals that we are given as answer choices. We can use the reactivity series to
put the given metals in order of reactivity. As you can see, based on the
series, sodium is the most reactive species. In fact, sodium is one of the most
reactive of all metals. This means that it is not a good
choice to be used as an electrolyte solution because it will spontaneously react
with any other metal and be very difficult to control. Therefore, sodium is generally
considered not to be a good candidate for an electrolyte solution.
All of the other metals listed,
gold, silver, chromium, and copper, can be used to electroplate another metal as
long as their reactivities are considered relative to the metal that is being
coated. Therefore, the metal that could not
be used for electroplating through the use of an aqueous solution is (D),
sodium.
