Effect of Electric Current on Substances
Conductors are substances that allow an electric current to pass through them. Non-conductors are substances which do not allow an electric current to pass through them.
By the end of this lesson you should be able to:
(i) Define the terms anode and cathode
(ii) Classify solutions and molten substances as either electrolytes and non-electrolytes
(iii) Define the terms electrolytes and non-electrolytes
Some substances conducts electricity in both molten and aqueous state.The setup below can be used to test for substances that conduct electricity in molten state.A rod of a metal or a non metal that is used to conduct electricity in a molten or aqueous state is known as an electrode. The negative electrode is called a cathode and the positive electrode is called an anode.
The setup below can be used to test for substances which conduct electricity in solid and molten state. The electrodes are dipped into different substances. Click on substance in both solid and molten state and observe if the bulb lights or not.
Lead (II) iodide and lead (II) bromide do not conduct an electric currect in solid state because their ions are held firmly by strong electro-static forces and this cannot move. However they conduct in molten state because melting weakens the electrostatic forces thus enabling the ions to move and thus conduct the electric current. Sugar and sulphur do NOT conduct electricity both in molten and solid state because they have molecular structures and lack charged particles to conduct the electric current.
Some substances conducts electricity in both molten and aqueous state. Others do NOT. The set -up below can be used to test for substances that conduct electricity in aqueous state.Click on each of the substances and identify whether the bulb lights in solid or aqueous state.
Click to play the following video to observe how aqueous solutions are tested for conductivity.
Aqueous solutions of salts, bases and dilute acids conduct electricity. Sodium chloride, copper (II) chloride and dilute hydrochloric acid conduct electricity. Sugar and urea do NOT conduct electricity. An aqeous solution or melt which conducts an electric current and is decomposed by it are called electrolytes. Aqeous or molten solutions that do NOT conduct an electric current are called non-electrolytes.
In this lesson, we shall discuss the effect of electric current on lead(II) bromide.
Ionic compounds do not conduct electricity in solid form. They conduct in molten or aqueous state.
By the end of the lesson, you should be able to state the products of electrolysis of a binary electrolyte.
The setup below can be used to show the effect of an electric current on molten lead (II) bromide. Click to view the reaction that takes place.
When an electric current is passed through lead (II) bromide it is decomposed into lead metal and bromine fumes. This process of decomposing an electrolyte by passing an electric current through it is called electrolysis.Molten lead (II) bromide is an example of a binary electrolyte. This is because its melt contains Lead (II) ions and Bromide ions only. Note that the experiment must be carried out in a fume chamber.This is because Bromine fumes produced are very poisonous.
Electrolysis is applied in such processes such as :
Extraction of metals such sodium, magnesium and aluminium by electrolysis of their molten compounds.
Extraction of Aluminium
Purification of metals such as copper
Electroplating of metals such as iron to improve their appearance and prevent corrosion.
Manufacture of pure chemicals such as sodium hydroxide.
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