Which of the following metal
electrodes is coated in metal using the electroplating experiment set up in the
diagram? (A) Electrode B, (B) electrode C,
(C) electrode D, or (D) electrode A.
To answer this question, we need to
understand how electrons flow in an electroplating electrolysis reaction. In an electrolysis reaction, a
power supply is used to generate an electric current that passes through a solution
containing ions ,which cause the ions to migrate to charged electrodes. These migrating ions can be metal
ions that are used to deposit a more desired type of metal onto the surface of
another metal. This process is known as
For example, iron, a strong metal
that is excellent for utensils like spoons but highly susceptible to rust, can be
coated with a metal like tin to avoid corrosion. A reaction like this would be
carried out in what is known as an electrolytic cell. These cells are set up very
specifically depending on the reaction that is needed.
An electrolytic cell contains an
electrolyte. The electrolyte solution allows the
circuit to connect between the two electrodes, supplying the metal ions that take
place in the reaction. The liquid state of the electrolyte
solution allows for the free movement of ions within the cell.
The movement of the metal ions is
influenced by the charge of the electrodes. Positive ions, cations, will flow
towards the negatively charged cathode. Likewise, the negatively charged
ions, anions, will flow to the positively charged anode.
Since we know where the ions will
flow, we can anticipate which electrode will be coated in the diagram in our
question. Our diagram shows two electrolytic
cells that are connected to one power supply with two different electrolyte
solutions. The electrolyte solution on the
left is sodium chloride, NaCl. The electrolyte solution on the
right is silver chloride, AgCl.
Both solutions will yield a
negatively charged chloride anion, Cl–, that will migrate to the positively charged
anodes. However, since chloride is not a
metal, the positively charged anodes will not be coated in metal. We can therefore eliminate answer
choices (B) and (D) because they state that the positively charged electrodes will
be coated in metal.
So what about the cations? The sodium chloride electrolyte
contains a sodium cation, Na+, that will migrate to the negatively charged
cathode. Since sodium is highly reactive, it
will not deposit onto the surface of an electrode like less reactive metals, such as
copper. Instead, hydrogen ions from the
water molecules within the aqueous solution will react at the electrode to form
The silver chloride electrolyte
solution on the right will yield a silver cation, Ag+, that will migrate towards the
negatively charged cathode. The silver metal cation will then
coat the cathode with pure silver metal, also known as electroplating. So since electrode D, the cathode
on the right side, is the only electrode in our apparatus that is coated in metal,
we can say that the correct answer is answer choice (C), electrode D.