Electrolytes

A compound which conducts electricity when dissolved in water or in molten state is called an electrolyte. For example, the aqueous solution of sodium chloride (NaCl), copper sulphate (CuSO₄), sodium hydroxide (NaOH) and silver nitrate (AgNO₃) are electrolytes. Actually when an electrolyte is dissolved in water then it splits into ions which are responsible for conduction of electricity.

Let us understand it more deeply, the table salt consists sodium ion (Na⁺) and chloride ion (Cl^–). In solid state the sodium ions are bound with chloride ions very strongly with the help of strong electrostatic forces. So, in the solid sodium chloride the ions are not free to move, thus it cannot conduct the electricity through itself in solid state. But when table salt is dissolved in water then the forces holding together the two ions are broken and the sodium ions and chloride ions become free to move in the aqueous solution. As both the ions have become free now so they can conduct electricity. This process of breaking sodium chloride into ions when dissolved in water can be represented as

This process of breaking compounds into ions by the action of water is called dissociation or ionization.

Now we have learnt that an electrolyte is a substance which conducts electricity when dissolved in water or in molten state by breaking into ions. But all the electrolytes do not ionize to the same extent. Depending on the extent of ionization, the electrolytes can be classified into two types.

    1. Strong electrolytes
    2. Weak electrolytes

Strong electrolytes

The electrolytes which ionize almost completely into ions in aqueous solution are called as strong electrolytes. E.g. HCl, H₂SO₄, HNO₃, NaOH, KOH, NaCl, KCl₃ etc. Usually all ionic compounds are strong electrolytes.

The equation for the ionization reactions of strong electrolytes are written with only single headed arrow directed to the right. For example:

or

HCl +H₂O           H₃O⁺ + Cl^–

Weak electrolytes

The electrolytes which ionize to a small extent in aqueous solution are called as weak electrolytes. E.g. CH₃COOH, NH₄OH, HCN etc. Usually all the covalent compounds are weak electrolytes.

In such cases, the molecules are in equilibrium with their ions. The ionization of such electrolytes is represented with the double headed arrows. For example:

CH₃COOH + H₂O            H₃O⁺ + CH₃COO^–

NH₃ + H₂O            NH₄⁺ + OH^–

Differences between strong electrolytes and weak electrolytes

Non electrolytes

The compounds which do not conduct electricity in molten state or in aqueous solution are known as non-electrolytes. For example, sugar, urea, glycerin etc.

Test your understanding and answer these questions:

1. What are electrolytes? Give examples.
2. Give differences between strong electrolytes and weak electrolytes.
3. What are non-electrolytes?