Answer:
The solutions which obey Raoult's law over
the entire range of concentration are known as ideal solutions. For an ideal
solution and .
The ideal behaviour of the solutions can be explained by considering two
components A and B.
In pure components, the intermolecular
attractive interactions will be of A?A type and B?B type, whereas in the binary
solutions in addition to these two, A?B type of interaction will also be
present. If A?A and B?B intermolecular forces are nearly equal to those between
A?B, this leads to the formation of ideal solution e.g., solution of n-hexane
and n-heptane.
When a solution does not
obey-Raoult's law over the entire range of concentration, then it is called
non-ideal solution. The vapour pressure of such a solution is either higher or
lower, than that predicted by Raoult's law.
If it is higher, the solution
exhibits positive deviation and if it is lower it exhibits negative
deviation from Raoult's law. In
case of positive deviation, A?B interactions are weaker than
those between A?A or B?B. i.e.,
the attractive forces between solute solvent molecules are weaker than those
between solute-solute and solvent-solvent molecules e.g., mixture of ethanol
and acetone.
For such solutions
On the other hand, in case of
negative deviation the intermolecular attractive forces between A - A and B?B
are weaker than those between A?B molecules. Thus, the escaping tendency of A
and B types of molecules from the solution becomes less than from the pure liquids
i.e., mixture of chloroform and acetone.
For such
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