Video Transcript
Consider the following galvanic
cell. Which of the following represents
the positive electrode of this cell? (A) Cu, solid; (B) Zn, solid; (C)
Cu2+, aqueous, one molar; (D) Zn2+, aqueous, one molar.
The question mentions a galvanic
cell. A galvanic cell can also be called
a voltaic cell. A galvanic cell is an
electrochemical cell in which a spontaneous redox reaction occurs, driving current
though the external circuit. The diagram shows the experimental
setup of the galvanic cell details mentioned in the question. These details are a simplified way
of writing the information shown in the diagram, and this expression is called the
cell notation. Sometimes, it is called the cell
diagram. This is the zinc half-cell. And this is its simplified
notation.
On the electrochemical series, we
would find that zinc has a more negative standard reduction potential than
copper. And so the zinc half-cell
information is written on the left. This is the copper half-cell. And this is its simplified
notation. On the electrochemical series, the
copper has a more positive standard reduction potential than zinc. And so the copper half-cell
information is written on the right-hand side of the cell notation.
We know that there are two
electrodes. These are placed in electrolyte
solutions. An electrode is a conductor through
which electrical current passes to an electrolyte. An electrolyte solution is a
solution which contains ions and thus can conduct electrical current. We are asked to determine which
electrode is the positive electrode. We can immediately eliminate answer
(C) and answer (D) as these represent electrolyte solutions, not metal
electrodes.
Notice the information about the
electrolytes in the two half-cells and their concentrations is written on either
side of the double line, which is shorthand for the salt bridge. To select whether copper or zinc is
the positive electrode, we need to understand the cell notation in more depth.
Typically, the anode half-cell
information is written on the left and the cathode information on the right. So the zinc half-cell is the anode
and the copper half-cell is the cathode. In a galvanic cell, oxidation
occurs at the anode. And this is the negative electrode
as electrons leave the electrode and travel up the wire oxidizing this
electrode. In a galvanic cell, reduction
occurs at the cathode. And this is the positive electrode
as electrons move towards this electrode in the wire reducing this electrode.
So which is the positive
electrode? The answer is (A) Cu, solid.
