The electrolytic cell
The set-up used to pass electricity through an electrolyte is shown in figure 12.2.2. Such an arrangement is called an electrolytic cell.
Figure to be added
What an electrolytic cell is made of
- A source that supplies electricity
- An electrolyte
- Two electrodes and connecting wires
Suppose the electrolyte is aqueous sodium chloride and electricity is supplied. Gas bubbles are seen coming off the carbon electrodes, so the aqueous solution has undergone a chemical change. In this way electrolysis can bring about a chemical reaction that does not normally happen by itself — a non-spontaneous reaction.
Why carbon or platinum
In the cells of 12.1 the electrodes themselves reacted: the zinc dissolved. In electrolysis we usually want to see what happens to the electrolyte, not to the electrodes, so they are made of something that does not react — carbon (graphite) or platinum. Such electrodes are called inert. They conduct electrons in and out and take no other part. When a reactive metal is used as an electrode instead, it can join in, and this is exactly what electroplating uses later in the chapter.
Two kinds of cell, two different set-ups
An electrochemical cell has no battery — it is the battery. An electrolytic cell always has an outside source of electricity. If a diagram shows a battery connected to the electrodes, it is electrolysis.
Source, electrolyte, two electrodes
An electrolytic cell is a source of electricity, an electrolyte, and two electrodes joined by wires. It drives reactions that would not happen by themselves.