Solution

By Vishwanath Maheshwary
Solution

•A homogenous mixture whose composition

varied within certain limits is termed a true
solution .
Types of Solution
Solute Solvent Example

Gas gas Air

Gas Liquid Aerated Water

Gas Solid Hydrogen in Palladium

Liquid Liquid Alcohol in water

Liquid Solid Mercury in zinc Amalgam

Solid Liquid Sugar in water

Solid Solid Various Alloys

•The solution of liquid in gas or solid in gas is
not possible because the constituents
cannot form a homogenous mixture .
•In this chapter we shall discuss only three
types of solutions
1) Gas in Liquid
2) Liquid in Liquid
3) Solid in Liquid
Solution
It is a homogenous mixture of two or more
components whose concentration can be varied within
certain limits . A solution containing Only two
components is termed a binary solution . One
component is called the solute while other as solvent .
The component having the same physical state , the
component present in larger proportion is termed the
solvent and the other component is called solute .
Solubility
A solution is said to be saturated when it contains as much as it can
dissolve at a particular temperature in presence of the undissolved
solute . A supersaturated solution contains more quantity and an
unsaturated solution contains less quantity of the solute than a
saturated solution .

The amount of the solute in grams which can dissolve at a particular

temperature in 100 grams of the solvent when the solution is saturated
is termed solubility of the solute.
Solubility of a gas in a liqid

Gases which can be easily liquified are more

soluble in common solvents . The gases
which form ions in water are highly soluble
soluble in water . The solubility of a gas
generally decreases with rise in temperature
and decrease in pressure.
Henry Law
Mass of gas dissolved per unit volume of a solvent is directly
proportional to the pressure of the gas at a given temperature . This is
Henry ‘s law

Where , m is the mass of gas dissolved per unit volume of solvent ,P is

pressure of the gas in equilibrium with the solution and K is
proportionality constant.
Henry’s Law Applications
To increase the solubility of CO2 in soft drinks and soda water . The
bottle is sealed under high pressure .
Henry’s Law Applications
Scuba divers must cope with high concentrations of dissolved gases
while breathing air at high pressure under water. Increased pressure
increases the solubility of atmospheric gases in blood . When the divers
come towards surface , the pressure gradually decreases . This releases
the dissolved gases and leads to the formation of bubbles of nitrogen in
the blood . This blocks capillaries and creates a medical condition
known as bends , which are painful and dangerous to life .
Scuba Diver
Henry’s Law Applications
To avoid bends , as well as , the toxic effects of high concentrations of
nitrogen in the blood, the tanks used by scuba divers are filled with air
diluted with helium (11.7% helium , 56.2% nitrogen and 32.1% oxygen).
Henry’s Law Applications
At high altitudes the partial pressure of oxygen is less than that at the
ground level . This leads to low concentrations of oxygen in the blood
and tissues of people living at high altitudes or climbers . Low blood
oxygen causes climbers to become weak and unable to think clearly .
Symptoms of a condition known as anoxia.
Anoxia
Solutions of liquids in Liquids
Miscible liquids from three types of solutions which may be ideal or
non-ideal solutions.
Ideal solution is that in which the attractive forces among the solute
and solvent molecules are of the same order as that of solute
intramolecular and solvent intramolecular forces . The
Raoult Law
The partial pressure of any volatile constituent of a solution at a
constant temperature is equal to the vapour pressure of pure
constituents multiplied by the mole fraction of that constituent in the
solution .
Raoult Law
1
The Solutions which obey Raoult Law over the entire range of
concentration are known as ideal solutions . The ideal solution have
two important properties .
1) The enthalpy of mixing of pure components to form the solutions is
zero.
2) The Volume of mixing is also zero .
Ideal Solution
Ideal solutions obey Raoult Law at all concentrations. Examples
1) Benzene and Toluene
2) Carbon tetrachloride and silicon tetrachloride
3) n-hexane and n-heptane
4) Ethylene dibromide and Ethylene dichloride
Positive deviation from Raoult’s Law
Examples of Positive Deviation
1)Water + Benzene
2)Water + Toluene
3)Methanol + Benzene
4)Ethanol + Toluene
Negative deviation from Raoult’s Law
Examples of Negative Deviation
1)Chloroform + Acetone
2)Chloroform + Ethyl amine
3)Strong Acid + water
HCl + H2O
H2SO4 +H2O
TXY Diagram
• A phase diagram in physical
chemistry, engineering, mineralogy, and materials science is a
type of chart used to show conditions (pressure, temperature,
volume, etc.) at which thermodynamically distinct phases (such
as solid, liquid or gaseous states) occur and coexist
at equilibrium
Azeotropic Mixtures
Such a mixture which boils at constant temperature and distils over
completely at the same temperature without any change in
composition , is called constant boiling mixture or azeotropic mixture .
Mixture % composition of Azeotrope Boiling Point

Water -Ethanol 95.97 Ethanol 78.15 degree celsius

Pyridine - water 57.00 pyridine 92.60 degree celsius

Ethanol - Benzene 32.40 Ethanol 67.80 degree celsius

Acetic Acid - Toluene 28.00 Acetic Acid 105.40 degree celsius

Azeotropic Mixture Graph
Types of Azeotropes

• Heterogeneous and Homogeneous Azeotropes

• Maximum boiling Azeotropes
• Minimum boiling Azeotropes
• Binary Azeotropes
Heterogeneous and Homogeneous
Azeotropes
If azeotropes are found in constitutions of mixtures and if they
are not completely miscible then they are termed as
heterogeneous azeotropes. Homogeneous Azeotropes are
azeotropes in which the constitutions of a mixture are miscible
completely. Hetero Azeotropic distillation comprises two liquid
phases.
Maximum boiling Azeotropes

• The liquid solution which show negative deviation from the ideal
solution boil at constant temperature which is higher than that
of pure component are called maximum boiling azeotropes
• Water boils at a hundred degree Celsius and hydrochloric acid
boil at around minus eight four degree Celsius, whereas
azeotropes boil at around hundred and ten degree Celsius
indicating that it has a higher boiling point than its constituents.
Minimum boiling Azeotropes

• The liquid solution which show positive deviation from the ideal
solution boil at constant temperature which is less than that of
pure component are called minimum boiling azeotropes.
• Water boils at a hundred degree Celsius, and ethanol boils at
around seventy-eight-degree Celsius, whereas azeotropes boil
at around seventy-eight-degree Celsius indicating that it has a
lower boiling point than its constituents.
Binary Azeotropes

Binary Azeotropes are azeotropes consisting of two constitutions

as mentioned above illustration. Ternary Azeotropes are
azeotropes consisting of more than three constitutions
Colligative property
• Dilute Solutions containing non volatile solute exhibit some special
properties which depend only upon the number of solute particles
present in the solution irrespective of their nature . These
properties are termed as colligative properties .
The Colligative properties are
1) Relative lowering in vapour Pressure
2) Elevation in Boiling point
3) Depression in the freezing point
4) Osmotic Pressure
Relative lowering in vapour presssure
• When a non-volatile solute is added ,to a solvent, the vapour pressure
is lowered
• [po-ps]/po = relative lowering in vapour pressure
• both rate of evaporation and vapour pressure are lowered.
Question
• The vapour pressure of pure benzene at a certain temperature is 640
mm Hg . A non-volatile solid weighing 2.175 g is added to39.0 g of
benzene . The vapour pressure of the solution is 600 mm Hg . What is
the molecular mass of solid substance ?
Ans 65.25
Question
• What mass of non-volatile solute (urea ) needs to be dissolved in
100 gm of water in order to decrease the vapour pressure of water
by 25% . What will be the molality of solution ?
Ans 111.1 gm , Molality= 18.52 m
Depression in Freezing Point (Cryoscopy )

Freezing point of a substance is defined as the temperature at which

the vapour pressure of its liquid is equal to the vapour pressure of the
corresponding solid .
Molal Depression Constant
• It is defined as the depression of freezing point produced when 1
mole of the solute is dissolved in 1000 gm of solvent .
Molal depression Constant of a particular solvent
and can be calculated from Thermodynamics
Anti Freeze Solutions
• Water is used in radiators of cars and other automobiles . In Cold
Countries where the atmospheric temperature becomes less than
zero degree, the water in the radiators would freeze .Anti-freeze
solutions are useful under these conditions when the vehicles are
used in the regions of sub-zero temperature so that the water does
not freeze in radiators .Such solutions are made by dissolving
ethylene glycol in water . Freezing point can be lowered to the extent
By varying the concentrations of ethylene glycol . Glycerol can also be
used as anti-freeze .
Question
By dissolving 13.6 g of a substance in 20 g of water , the freezing point
Decreased by 3.7 degree Celsius . Calculate the molecular mass of the
substance . Molal depression constant for water = 1.863 K Kg/ mol
Ans =342.39
Question
Two Elements A and B form compounds having molecular formulae
AB2 and AB4 . When dissolved in 20.0 g of benzene, 1.0 g of AB2
lowers the freezing point by 2.3 degree Celsius , whereas 1.0 gm of
AB4 lowers the freezing point by 1.3 degree Celsius . The molal
depression constant for benzene is 5.1 . Calculate the atomic masses of
A and B ?
Ans Atomic mass of A and B are 25.57 and
42.645
Elevation in Boiling Point (Ebullioscopy )
• The boiling point of a liquid is the temperature at which its
vapour pressure is equal to the atmospheric pressure

• The difference in the boiling point of the pure solvent is termed as

elevation of boiling point .
Beckmann’s thermometer
Molal Elevation Constant OR Ebullioscopic
Constant
• It is defined as the elevation in boiling point when 1 mole of the
solute is dissolved in 1000 gm of solvent .
Molal Elevation constant is characteristic of a
particular solvent and can be calculated from
the thermodynamical relationship .
Question
• On dissolving 10.8 g of glucose in 240 g of water , its boiling point
increases by 0.13 degree Celsius . Calculate the molal elevation
constant of water
Ans .52
Question
• A Solution of 2.5 g of a non volatile solid in 100 g benzene is boiled at
0.42 degree Celsius higher than the boiling point of pure benzene
. Calculate the molecular mass of the substance
Molal elevation constant of benzene is 2.67 K Kg / mol
Ans 158.9
Depression in freezing Point (Cryoscopy )
• Freezing point of a substance is defined as the temperature at which
the vapour pressure of its liquid is equal to the vapour pressure of the
corresponding solid
• ΔT = molaity * Kf
Osmosis and Osmotic Pressure
Osmosis is defined as the spontaneous flow of solvent molecules
through semipermeable membrane from a pure solvent or from a
dilute to a concentrated solution .
Osmotic Pressure
• The hydrostatic pressure developed as a result of osmosis is a
measure of osmotic pressure of the Solution .
Semipermeable Membrane
A membrane which allows the solvent molecules to pass through it
but prevents the passage of solute molecules through it is called a
semipermeable membrane .
Measurements of osmotic pressure provides another method of
determining molar masses of solutes. This method is widely used to
determine molar masses of solutes . This method is widely used to
determine molar masses of proteins , proteins , polymers and other
macromolecules . The osmotic pressure method has the advantage
over other methods as the measurement is around room temperature
and the molarity is used instead of molality .
Reverse Osmosis
• The direction of osmosis can be reversed if a pressure larger than the
osmotic pressure is applied to the solution side. That is, now the pure
solvent flows out of the solution through the semi permeable
membrane. This phenomenon is called reverse osmosis and is of great
practical utility. Reverse osmosis is used in desalination of sea water.
A schematic set up for the process. When pressure more than
osmotic pressure is applied, pure water is squeezed out of the sea
water through the membrane. A variety of polymer membranes are
available for this purpose.
• The pressure required for the reverse osmosis is quite high. A
workable porous membrane is a film of cellulose acetate placed over
a suitable support. Cellulose acetate is permeable to water but
impermeable to impurities and ions present in sea water. These days
many countries use desalination plants to meet their potable water
requirements.
As compared to other colligative properties , its magnitude is large
even for very dilute solutions . The technique of osmotic pressure for
determination of molar mass of solutes is particularly useful for
biomolecules as they are generally not stable at higher temperatures
and polymers have poor solubility .
Question
200 cm3 of an aqueous solution containing 1.26 g of a polymer . The
Osmotic pressure of such solution at 300K is found to be 2.57 x 10-3
Bar . Calculate the molar mass of the polymer .
Ans 61038
Question
A solution is prepared by dissolving 1.08 g of human serum albumin , a
Protein obtained from blood plasma , in 50 cm3 of aqueous solution .
The solution has an osmotic pressure of 5.85 mm Hg at 298 K.
A)What is molar mass of albumin ?
B) What is height of water column placed in solution ?
density of water = 1g/cm3
Molecular Mass= 68655
Height = 7.958x106
Degree of Dissociation
It is the number of moles dissociated in one mole of substance .
Van’t Hoff Factor i
When the solute undergoes dissociation or association in solution , the
number of particles in solution increases or decreases and thus the
colligative property changes accordingly . In 1896, van’t Hoff
introduced a factor i known as van’t Hoff factor to express the extent of
Dissociation or association of the solute in Solution .
Van’t Hoff factor i and Degree of Dissociation
Van’t Hoff factor i and Degree of Association
Question
Phenol associates in benzene to a certain extent for a dimer . A
solution containing 20 x 10-3 kg of phenol in 1 kg of benzene has its
freezing point decreased by 0.69 K . Calculate the fraction of the
phenol that has been dimerized ? Kf of benzene is 5.12 degree Kelvin
Kg /Mole
Ans 73.3 % or 0.733
Question
The freezing point depression of .001 m . Kx[Fe(CN)]6 is 7.10 x 10-3 K .
Determine the value of x . Given Kf = 1.86 K Kg /mol for water.
X=2.817 =3
Question
The freezing point of a solution containing 0.2 g of acetic acid in 20 g
of benzene is lowered by 0.45 degree Celsius . Calculate the degree of
association of acetic acid ( dimer formation ) in benzene .
(Kf for benzene is 5.12 K Kg / mol )
Ans 94.5 % associated