Ionic equilibrium
Electrolytes
These are
the substances which in their molten state or in aqueous solution contain ions
and, therefore, conduct electricity.
For
example, sodium chloride, hydrochloric acid, acetic acid. Are electrolytes.
Non-electrolytes
These are
the substances which do not conduct electricity either in solution or in molten
state.
For example,
Glucose, sugar, benzene etc:
Types of ElectrolytesElectrolytes are of two types:
(a) Strong electrolytes. These are the
substances which ionise almost completely when dissolved in water.
Examples are strong acids, strong bases and salts. HCL, NaCL, NaOH etc.
are strong electrolytes. Since these are completely ionised in solution, the
law of chemical equilibrium is not applicable on them.
(b) Weak electrolytes. These are the
electrolytes which ionise to a very small extent when dissolved in water.
Ex: - weak acid and weak bases CH3COOH, NH4OH etc. Are weak electrolytes:
Since weak electrolytes are not only slightly ionised, there will
establish equilibrium between the ions and unionised molecules at a particular
temperature: Hence, law of chemical
equilibrium can be applied on weak electrolytes:
Ionic Equilibrium in Aqueous solutions
A substance which is only partially ionised in
solution and hence show low electrical conductivity is called weak
electrolytes. Some examples of weak electrolytes are NH4OH, acetic acid oxalic
acid etc.
The fraction of the total number
of molecules of electrolytes which splits up into ions is called degree of
ionisation.
Thus,
degree of ionisation,
α= Number of molecules of
electrolytes which splits up into ions /Total
number of molecules of electrolyte
It may note that more the ion producing
ability of a substance more is its electrical conductivity in solution. Weak electrolytes
in aqueous solution exist as ions in equilibrium with undissociated molecule. The
ionic equilibrium established in weak electrolyte is dynamic in nature.
Ionic equilibrium
is defined as the dynamic equilibrium established between the ions and unionised
molecules of weak electrolyte are solution.
Concepts of Salts
Salts are crystalline
solid compounds that are formed from neutralisation reactions of aqueous strong
acid and strong bases. If either acid or base is weak, the salt undergoes
hydrolysis to gives acidic or basic
solutions. Salts are various types
Normal salt:
These are
formed by the replacement of all replaceable hydrogen atoms as H+ ions
Ex:- NaCl,
KNO3, Na2SO4
Acidic salt:
Acidic salts
are formed by incomplete neutralisations of polybasic acids. Such salts still contain
one or more hydrogen atoms which can be replaced.
Ex:- NaHCO3,
NaHSO4, NaH2PO4,Na2HPO4 etc.
Basic salt:
This salt
is formed by the incomplete neutralisation of polybasic bases. Such of these salts
are still contains some hydroxyls group.
Ex:- Mg(OH)Cl,
Zn(OH)Cl, Fe(OH)2Cl etc.
Double salt:
This salt is
the addition compounds formed by the combination of two simple salts. Such salts
are stable in the solid state.
Ex: - K2SO4Al2(SO4)324H2O,
FeSO4(NH4)2 SO4 6H2O etc.
Complex salts:
These are
the compounds formed by the combination of simple salts or molecular compounds.
These are stable in the solid state as well as in solution.
Ex: - K4[Fe(CN)6],
[Cu (NH3)4]SO4 etc.
The properties
of complex salts are different form their constituents.
Mixed salt:
These are
the salts which furnish more than one cation or more than one anion when
dissolved in water.
Ex: - CaOCL2,
NaKSO4, NaNH4HPO4 etc.
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