1.4 Electrolytic cell
In galvanic cells, chemical changes are used to produce electricity. The reverse process using electricity to produce chemical changes occurs in electrolytic cells. That is:
electrolysis
Chemical changes Electrical energy
This process is known as electrolysis.
Electrolysis is the decomposition of a compound by the use of electricity.
The apparatus used for electrolysis is called an electrolytic cell (Figure 1.47). It consists of two electrodes in a liquid electrolyte. A direct current (d.c.) power source is connected to the electrodes. An electric current flows through the electrolyte, decomposing it into simpler substances.
Note: Be careful not to confuse the electrolytic cell with the galvanic cell. In an electrolytic cell, the anode is the positive electrode while the cathode is the negative electrode. However, oxidation still occurs at the anode and reduction at the cathode.
The terms commonly used in electrolysis are shown in Figure 1.47.
An electrolyte is an ionic compound which, when molten or in an aqueous solution, conducts an electric current and is decomposed in the process.
An electrode is a rod or plate where electricity enters or leaves an electrolyte during electrolysis. Reactions occur at the electrodes (not in the electrolyte).
The anode is the positive electrode connected to the positive terminal of the d.c. power soure. Oxidation occurs at the anode.
The cathode is the negative electrode connected to the negative terminal of the d.c. power source. Reduction occurs at the cathode.
An anion is an ion with a negative charge. During electrolysis, it is attracted to the anode.
A cation is an ion with a positive charge. During electrolysis, it is attracted to the cathode.
Previously, you learnt that ionic compounds consist of ions. In this section you will see that electrolysis provides actual evidence for the existence of ions.