Electroplating
The decomposition (breakdown) of a compound using an electric current. is used to electroplate objects (coat them with a thin layer of metal). This is useful for coating a cheaper metal with a more expensive one, such as copper or silver.
How it works
- The negativeA conductor used to establish electrical contact with a circuit. The electrode attached to the negative terminal of a battery is called a negative electrode, or cathode. The electrode attached to the positive terminal of a battery is the positive electrode, or anode. should be the object to be electroplated.
- The positive electrode should be the metal that you want to coat the object with.
- The A substance which, when molten or in solution, will conduct an electric current. should be a solution of the coating metal, such as its metal nitrate or sulfate.
Here are two examples.
Electroplating with silver
The object to be plated, such as a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.
Electroplating with copper
The object to be plated, such as a metal pan, is connected to the negative terminal of the power supply. A piece of copper is connected to the positive terminal. The electrolyte is copper(II) sulfate solution.
Purifying copper by electrolysis [Higher tier only]
Copper is purified by electrolysis. Electricity is passed through solutions containing copper compounds, such as copper(II) sulfate. The anode (positive electrode) is made from impure copper and the cathode (negative electrode) is made from pure copper.
Pure copper forms on the cathode. The slideshow shows how this works.
Image caption, Purifying copper by electrolysis
1. A beaker with pure and impure copper rods dipped into copper(II) sulfate solution
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During electrolysis, the anode loses mass as copper dissolves, and the cathode gains mass as copper is deposited.
The slideshow shows what happens during the purification of copper by electrolysis:
Image caption, The purification of copper by electrolysis
1. Four Cu ions are attached to the rod on the right, and four Cu2+ ions are floating in the space between the rods
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A half-equation shows what happens at one of the electrodes during electrolysis. Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. are shown as e–.
These are the half-equations:
- at the anode, Cu → Cu2+ + 2e– (The gain of oxygen, or loss of electrons, by a substance during a chemical reaction.)
- at the cathode, Cu2+ + 2e– → Cu (The loss of oxygen, gain of electrons, or gain of hydrogen by a substance during a chemical reaction.)
Oxidation happens at the anode because electrons are lost. Reduction happens at the cathode because electrons are gained.
One way to remember this is by using the mnemonic OIL RIG:
Oxidation Is Loss of electrons, Reduction Is Gain of electrons.
