CBSE CLASS -12 NOTES ON IDEAL SOLUTION
A binary liquid - liquid solution is said to be ideal if it obeys Raoult’ s Law over the entire range
of concentration. This means that vapour pressure of each component of the solution should be
equal to the product of vapour pressure of that component in pure states and its mole fraction in
the solution and the total pressure of the solution equal to the sum of partial vapour pressures
of components of the solution.
Suppose two liquid components A and B form a binary solution, AB . The vapour pressure of
components A and B in their pure states are pA0 and pB0 respectively and their mole fractions in
solution are xA and xB respectively. The solution will be ideal if
pA = pA0 xA and pB = pB0 xB
ptotal = pA0 xA + pB0xB
An ideal solution is characterized by following two important characteristics.
1. Enthalpy change on mixing (∆mixH ) is zero i.e. no heat is evolved or absorbed when
components are mixed.
2. Volume change on mixing ( ∆mix V) is also zero. This means neither volume increases
nor decreases. The total volume of solution is equal to the sum of volumes of the two
components.
Both of these characteristics are due to the existence of intermolecular attractive forces ( A - B
interactions ) of the same strength as in pure components. ( A -A and B- B interactions).When
vapour pressure ( pA and pB) of a component of an ideal solution is plotted against mole
fraction ( xA and xB) , a linear plot is observed. It indicates that vapour pressure of each
component is directly proportional to its mole fraction in the solution.
Reason for ideal behavior :
Ideal behaviour of a solution is due to the same magnitude of intermolecular attractive forces
between two components as the attractive interactions in pure components . This means the
new intermolecular interaction ( A- B type interaction) between two components A and B are of
the same strength as in pure components A ( A-A type interaction ) and B ( B-B type
interaction).
Examples of Ideal solutions :
Ideal solutions are rare but some binary solutions are nearly ideal in behaviour . These solutions
are -
(1) n -Hexane and n - Heptane
(2) Chlorobenzene and Bromobenzene
(3) Benzene and Toluene
(4) Bromoethane and Iodoethane
The concept of ideal solution is important in chemistry, as it helps us understand the properties
of liquid mixtures such as vapour pressure , boiling point , freezing point, density, viscosity ,
refractive index etc.
A binary liquid - liquid solution is said to be ideal if it obeys Raoult’ s Law over the entire range
of concentration. This means that vapour pressure of each component of the solution should be
equal to the product of vapour pressure of that component in pure states and its mole fraction in
the solution and the total pressure of the solution equal to the sum of partial vapour pressures
of components of the solution.
Suppose two liquid components A and B form a binary solution, AB . The vapour pressure of
components A and B in their pure states are pA0 and pB0 respectively and their mole fractions in
solution are xA and xB respectively. The solution will be ideal if
pA = pA0 xA and pB = pB0 xB
ptotal = pA0 xA + pB0xB
An ideal solution is characterized by following two important characteristics.
1. Enthalpy change on mixing (∆mixH ) is zero i.e. no heat is evolved or absorbed when
components are mixed.
2. Volume change on mixing ( ∆mix V) is also zero. This means neither volume increases
nor decreases. The total volume of solution is equal to the sum of volumes of the two
components.
Both of these characteristics are due to the existence of intermolecular attractive forces ( A - B
interactions ) of the same strength as in pure components. ( A -A and B- B interactions).When
vapour pressure ( pA and pB) of a component of an ideal solution is plotted against mole
fraction ( xA and xB) , a linear plot is observed. It indicates that vapour pressure of each
component is directly proportional to its mole fraction in the solution.
Reason for ideal behavior :
Ideal behaviour of a solution is due to the same magnitude of intermolecular attractive forces
between two components as the attractive interactions in pure components . This means the
new intermolecular interaction ( A- B type interaction) between two components A and B are of
the same strength as in pure components A ( A-A type interaction ) and B ( B-B type
interaction).
Examples of Ideal solutions :
Ideal solutions are rare but some binary solutions are nearly ideal in behaviour . These solutions
are -
(1) n -Hexane and n - Heptane
(2) Chlorobenzene and Bromobenzene
(3) Benzene and Toluene
(4) Bromoethane and Iodoethane
The concept of ideal solution is important in chemistry, as it helps us understand the properties
of liquid mixtures such as vapour pressure , boiling point , freezing point, density, viscosity ,
refractive index etc.
