We have all experienced electric current making a bulb glow, a fan rotate or a heater warm. But does electric current do anything when it passes through a liquid? The answer is yes — and the effects can be quite dramatic. When electric current passes through certain liquids, it can decompose them chemically, deposit metals, and even bubble out gases. These are called the chemical effects of electric current.
Some liquids allow electric current to flow through them and are called conductors, while others do not and are called insulators. When current flows through a conducting liquid, chemical reactions take place at the electrodes — a process that forms the basis of electroplating, electrorefining and the production of many metals. In this chapter we explore conductors and insulators, the chemical changes caused by electric current, and the important industrial applications of these effects.
Materials can be classified on the basis of their ability to conduct electricity:
Interesting points: - Pure distilled water is an insulator because it has no dissolved salts to carry charge. But when common salt, acid or a few drops of a base are dissolved in it, the water becomes a good conductor because the dissolved substances break into ions that carry the current. - Graphite is a non-metal but it conducts electricity, which is why it is used in electrodes. - Tap water, rain water and sea water conduct electricity because they contain dissolved salts and minerals.
Not all liquids conduct electricity. The ability of a liquid to conduct depends on the presence of ions (charged particles) in it.
To test whether a liquid conducts, we can set up a circuit with two electrodes (usually carbon rods or metal strips) dipped in the liquid, connected to a battery and a bulb or a compass needle. If the bulb glows, or if a magnetic compass near a wire shows deflection (indicating current), the liquid conducts.
When electric current passes through a conducting solution, chemical reactions take place at the electrodes. The main chemical effects are:
These changes occur because the electric current causes ions in the solution to move and react at the electrodes. This process, in which a compound is broken down into its constituents by passing electric current through its solution, is called electrolysis. The two rods/strips dipped in the solution are called electrodes — the electrode connected to the positive terminal of the battery is the anode, and the one connected to the negative terminal is the cathode.
The most important application of the chemical effect of electric current is electroplating. Electroplating is the process of depositing a thin layer of one metal on another metal object by passing electric current through a solution of a salt of the metal to be deposited.
Why electroplating is done: - To prevent rusting (corrosion) — iron objects are plated with zinc (galvanisation) or with chromium to prevent rusting. - To make objects appear attractive — jewellery is plated with gold or silver to give a shiny, expensive look. - To make objects durable and improve their surface — car bumpers are plated with chromium, and tin is plated on iron to make cans.
Example of electroplating: To electroplate an iron spoon with copper, the spoon is made the cathode (negative electrode), a pure copper plate is made the anode, and both are dipped in a copper sulphate solution. When current passes, copper from the solution gets deposited on the spoon, and the copper from the anode dissolves to replenish the solution.
Artificial jewellery is often electroplated with silver or gold to give it an attractive and expensive appearance without the cost of the actual precious metal. In such cases, the article to be plated is made the cathode and a bar of pure silver or gold is made the anode, immersed in a suitable salt solution. The thin layer of silver or gold deposited on the base metal makes the jewellery shine like the real thing.
Electroplating is used extensively in daily life:
Electroplating does not use up the metal of the article; it only deposits a thin protective and decorative layer, which saves precious metals and protects the base metal.
| Feature | Conductors | Insulators |
|---|---|---|
| Allow current | Yes | No |
| Examples | Copper, aluminium, graphite, salt solution | Rubber, plastic, wood, glass, pure water |
| Reason | Have free charges (electrons/ions) | Do not have free charges |
| Conduct Electricity | Do Not Conduct |
|---|---|
| Tap water (dissolved salts) | Pure/distilled water |
| Salt solution | Sugar solution |
| Acid solution | Alcohol |
| Base solution | Kerosene |
| Metal Plated | Base Metal/Article | Purpose |
|---|---|---|
| Chromium | Car bumpers, taps | Prevent rusting, shiny look |
| Zinc | Iron sheets, wires | Prevent rusting (galvanisation) |
| Tin | Iron sheets for cans | Prevent rusting, safe for food |
| Gold/Silver | Artificial jewellery | Attractive, expensive look |
| Nickel | Tools, machine parts | Resist corrosion |
The chemical effects of electric current reveal a hidden world of change inside liquids. Conductors such as metals, graphite and ionic solutions allow current to pass, while insulators like rubber and pure water do not. When current flows through a conducting solution, it produces bubbles of gas, deposits of metal and colour changes at the electrodes — chemical effects that form the basis of electrolysis and electroplating. Electroplating, in which a thin layer of metal such as copper, zinc, chromium, tin, silver or gold is deposited on another object, protects metals from rusting and gives articles a beautiful, durable finish. From the shiny bumpers of cars to the glitter of artificial jewellery, the chemical effects of electric current are quietly at work all around us.