Video Transcript
A student electroplates a key with
copper. What aqueous solution and electrode
would be the best choices for this experiment? (A) H2SO4 aqueous and a graphite
electrode. (B) H2SO4 aqueous and a platinum
electrode. (C) NaOH aqueous and a copper
electrode. (D) CuSO4 aqueous and a graphite
electrode. (E) CuSO4 aqueous and a copper
electrode.
Electroplating involves the use of
an electrolytic cell to deposit a thin layer of metal onto another metal
surface. An electrolytic cell needs a power
supply. In this experiment, a simple cell
is used to provide the direct current electricity. Our simple cell has a positive
terminal and a negative terminal. The positive terminal is called the
anode. And at the anode, we would expect
to find a source of the metal that is going to provide the plating.
In this scenario, the metal that is
providing the plating is copper. So in this experiment, the anode
needs to be an electrode made from a piece of pure copper. At this electrode, copper two plus
ions will be produced. Copper atoms from the anode will
leave two electrons behind on the anode, and they will enter the solution as copper
two plus ions. The anode is therefore the site of
oxidation here, and the electrons will flow from the anode to the cathode, which is
the negative electrode.
In order to plate the key, which is
placed at the cathode in this circuit, with copper, we need copper ions to move
through the solution and become copper atoms again at the cathode. Since we need a copper electrode to
maintain the concentration of copper ions in the solution, we can reject any answers
that suggest any other electrode should be used. Answers (A), (B), and (D) are
therefore not correct. Graphite is a form of carbon, and
it won’t provide any copper ions at all. Platinum is a completely inert
metal, and it won’t provide ions either.
The aqueous solution in the
electrolytic cell must contain dissolved copper ions. These copper two plus ions will
move to the cathode where they will gain two electrons and become copper atoms
again, plating the key. This is the site of reduction. Since the solution must contain
copper two plus ions, we can reject answer (C). In answer (C), we see a solution of
sodium hydroxide. Aqueous sodium hydroxide will
contain aqueous sodium ions and aqueous hydroxide ions. These can be written as Na+ (aq)
and OH− (aq). Aqueous sodium hydroxide will not
yield any copper two plus ions, so it’s not the right answer here. Aqueous copper sulfate or CuSO4
(aq) does yield aqueous copper two plus ions. Answer (E) is the correct answer as
we have the correct solution and the correct electrode.
