EQUILIBRIUM IN IONIC REACTIONS
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
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:
HCl +H2O H3O+ + Cl-
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
|S No.||Strong electrolytes||Weak electrolytes|
|1.||The electrolytes which ionize almost completely into ions in aqueous solution are called as strong electrolytes.||The electrolytes which ionize to a small extent in aqueous solution are called as weak electrolytes.|
|2.||The equation for the ionization reactions of strong electrolytes are written with only single headed arrow directed to the right.||The ionization of such electrolytes is represented with the double headed arrows.|
|3.||Usually all ionic compounds are strong electrolytes.||Usually all the covalent compounds are weak electrolytes.|
|4.||Examples:- HCl, H2SO4, HNO3, NaOH, KOH, NaCl, KCl3 etc.||Examples :- CH3COOH, NH4OH, HCN etc.|
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.
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