Galvanic Cells

An electrochemical reaction is a process where electrons are transferred between two substances, with one losing electrons and the other gaining them. When a substance loses electrons, we say that it has undergone oxidation or that it has been oxidized. When it gains electrons, we say that it has undergone reduction or has been reduced. To help you distinguish between the two, remember the phrase 'oil rig,' which stands for oxidation is losing, reduction is gaining. Some electrochemical reactions occur spontaneously, which we can study in a galvanic cell.

The galvanic cell has four main parts. First, there are two metal electrodes, each of which is immersed into a different electrolyte solution. The solutions consist of the ions needed for the half-reactions, either the oxidation or reduction reaction, that occur at each electrode. The solutions are connected by a salt bridge, which enables the flow of ions and maintains the charge neutrality of the solutions. The electrodes are connected by an external circuit, which the electrons travel through during the reaction.

The anode is the electrode that gives up electrons in the reaction or is oxidized. The cathode is the electrode that gains electrons and is reduced. To help you distinguish between these two labels, remember the phrase 'red cat,' since reduction occurs at the cathode.

So how do we know which metal acts as the anode and which acts as the cathode? We can use the standard electrode potential of the metal, which is a measure of the metal’s tendency to lose electrons. A more negative electrode potential means that the metal has a higher tendency to lose electrons. Electrons always flow from the metal with the lower standard potential to the metal with the greater standard potential.

In a galvanic cell, electrons flow from the anode to the cathode, thus the anode is the metal with the lower standard potential, and the cathode is the metal with the higher standard potential. As the electrons travel between the two electrodes, an electric potential is measured. The magnitude of the voltage produced is equal to the standard potential of the cathode minus the standard potential of the anode.

So, if two metals with similar standard electrode potentials are used in the galvanic cell, like lead and tin, for example, the magnitude of voltage produced will be low. If the metals have different standard potentials, like silver and magnesium, the voltage produced will be high.

In this lab, you will construct a galvanic cell using two metal electrodes and measure the potential produced as the oxidation and reduction reactions occur. You'll then identify unknown metal electrodes using known standard potentials and determine the magnitude of the voltage produced.