Chemistry Solutions

1. SOLUTIONS
CLASS XII
CHAPTER-2

2. Solutions are homogeneous mixture of two
or more substance.
In a binary solution the component present
in less amount is called solute which gets
dissolved in a solvent.
The component present in large amount is
called solvent which dissolve the solute in it.
2

3. TYPES OF SOLUTION BASED ON PHYSICAL STATE OF
SOLUTE AND SOLVENT
3

4. WAYS OF EXPRESSING CONCENTRATION OF SOLUTION
CONCENTRATION OF
SOLUTION
4

5. 5
SOLUBILITY OF SOLIDS IN LIQUIDS
It depends on
• nature of solute and solvent - “Like dissolves like.”
• temperature
• Pressure
If the dissolution process(solute + solvent =solution) is
endothermic(ΔsolH>0 ) , the solubility should increase with rise in
temperature.
If the dissolution process is exothermic ( ΔsolH < 0) , the solubility
should decrease
Pressure does not have any significant effect on solubility of
solids in liquids as they are highly incompressible.
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6. 6
SOLUBILITY OF GAS IN LIQUID
Solubility of gas in liquid decreases with in increase
temperature as the dissolution process is generally
exothermic.
Effect of Pressure.-Governed by Henry’s law
The law states that the partial pressure of the gas above the
liquid is proportional to the mole fraction(solubility) of
the gas (x)in the solution.
p= KH X
where KH is the Henrys law constant.
Kh is a function of nature of gas,and varies
inversely with solubility and directly with
temperature.
6

7. APPLICATIONS OF HENRY’S LAW
1. Soft drinks :To increase the solubility of CO2 in soft
drinks and soda water ,the bottle is sealed under
high pressure.
2. Bends in scuba divers: He is added to the oxygen
cylinders to reduce bends as it is less soluble in
blood.
3. Anoxia : Low oxygen concentration in the blood of
mountaineers or people living in high altitude due to
less amount of oxygen in air.
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8. 8

9. 9
RAOULTS LAW FOR SOLUTION CONTAINING NON-VOLATILE
COMPONENT
For solution containing non volatile solute the
vapour pressure exerted is less than the pure
solvent as some solute occupies the surface of
the liquid.
Raoults law states that pressure exerted by
solution is same as the partial pressure exerted
by the solvent, which is directly proportional to
mole fraction of the solvent in solution.
For non-volatile solute Raoults law also states that the relative
lowering of vapour pressure is equal to mole fraction of the solute

10. IDEAL SOUTION
 obey Raoults law at all concentrations.
 ΔV mixing =0
 ΔH mixing =0
 A-B interaction =A-A or B-B interaction
eg: (a) solution of n-hexane and n-heptane
(b) solution of bromoethane and chloroethane
( c ) solution of benzene and toluene
10

11. NON-IDEAL SOLUTION
SOLUTIONS SHOWING POSITIVE DEVIATION
• Do not obey Raouts law and shows
positive deviation from ideal
Behaviour
• A-B interaction < A - A or B - B interaction.
• ΔV mixing > 0
• ΔH mixing > 0
• Eg : mixture of cyclohexane and ethanol
11

12. NON-IDEAL SOLUTIONS
SOLUTIONS SHOWING NEGATIVE DEVIATIONS
 Do not obey Raoults law and shows negative
deviation from ideal behaviour
 A-B interaction > A-A or B-B interaction.
 ΔV mixing <0
 ΔH mixing < 0
 Eg : mixture of Acetone and chloroform
12

13. AZEOTROPES
(CONSTANT BOILING MIXTURE)
Azeotropes are binary liquid mixtures having definite
composition ,which boils at a constant temperature
and has same composition in vapor phase & liquid
phase and can distil out as if it were pure liquids.

14. 14
AZEOTROPES
Minimum boiling azeotopes Maximum boiling azeotrope
This type if azeotrope is formed by
those liquid mixtures which shows
positive deviation from ideal
behaviour.
The azeotrope boil at a temperature
lower than the boiling point of the
two liquids.
Eg. Ethanol & water system forms
minimum boiling azeotrope with
composition 95% ethanol & 5% H2O.
This type if azeotrope is formed by
those liquid mixtures which shows
negative deviation from ideal
behaviour.
The azeotrope boil at a
temperature higher than the
boiling point of the two liquids.
Eg. HNO3 & water system forms a
maximum boiling azeotrope with
composition 68% nitric acid &
32% H2O.

15. 15
cco
Colligative
properties
Depends on the
number of solute
particles
OSMOTIC
PRESSURE
RELATIVE
LOWERING OF
VAPOUR
PRESSURE
ELEVATION IN
BOILING
POINT
DEPRESSION
IN FREEZING
POINT

16. 16
RELATIVE LOWERING OF VAPOUR PRESSURE:
For a solution containing non volatile solute, the partial pressure
exerted by the solvent is directly proportional to the mole fraction of the
solvent,
Calculation of molar mass of solute

17. Kb is called molal elevation constant/
ebulioscopic constant
Calculation of molar mass of solute

18. 18
Kf is called molal depression
constant /cryoscopic constant.
Calculation of molar mass of solute

19. OSMOTIC PRESSURE
Osmosis: If a solvent and solution are separated by a semipermeable
membrane ,the solvent molecules will flow through the membrane from
pure solvent to solution. This process of flow of solvent is called osmosis.
The excess pressure applied on solution to just prevent osmosis is called
osmotic pressure. 19

20. MOLAR MASS AND OSMOTIC PRESSURE
π α C T , c is the molar concentration.
π = C R T
Calculation of molar mass
𝝅 =
𝒏𝑩
𝑽
×RT But 𝒏𝑩 =
𝑾𝑩
𝑴𝑩
𝑴𝑩 =
𝑾𝑩 × 𝑹 × 𝑻
𝝅𝑽
20

21. ISOTONIC SOLUTIONS
Two solutions having same osmotic pressure at a given
temperature are called isotonic solutions.
π1 = π2
Among two solutions, one having higher osmotic pressure
is called hypertonic solution and that having lower osmotic
pressure is called hypotonic solution.
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22. REVERSE OSMOSIS AND WATER PURIFICATION
The direction of osmosis can be reversed if a pressure larger than the
osmotic pressure is applied to the solution side . This phenomenon is
called reverse osmosis.
Reverse osmosis is used in desalination of sea water using cellulose
acetate as the SPM.
22

23. ABNORMAL MOLAR MASS
When solute undergoes association or dissociation, the molar mass obtained by
colligative property measurement is different from the actual value. This is called
abnormal molar mass.
(i) If association take place, number of particles decrease and the molar mass
increases.
(ii) If dissociation take place , number of particles increase and molar mass decrease
molar mass decreases
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24. 24
If i = 1 neither association nor dissociation.
If i > 1, dissociation
If i < 1 , association
MODIFIED EQUATONS FOR
COLLIGATIVE PROPERTY DEGREE OF DISSOCIATION Degree of association
 =
𝒊−𝟏
𝒎−𝟏
where m = no. of particles
formed by dissolution of each
molecules.
 =
𝑖−1
1
𝑚
−1
where m = no. of particle of
solute particle which associate
to give one molecules.