The document is a lecture on solutions and their properties presented by Dr. Basavaraj K. Nanjwade from Omer Al-Mukhtar University in Libya. It covers topics such as definition of solutions, preparation of solutions, types of solutions, solvent-solute interactions, solubility of gases, liquids and solids in liquids, factors affecting solubility, distribution phenomenon, colligative properties including lowering of vapor pressure, depression of freezing point and osmotic pressure.

1. Solutions and Their Properties
Dr. Basavaraj K. Nanjwade M. Pharm., Ph. D
Department of Pharmaceutics
Faculty of Pharmacy
Omer Al-Mukhtar University
Tobruk, Libya.
E-mail: nanjwadebk@gmail.com
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

2. CONTENTS
1. Definition, preparation of solutions, types of solutions.
2. Solvent-solute interaction and thermodynamics of
solvents.
3. Solubility of gases in liquids and liquids in liquids.
4. Solubility of solids in liquids (electrolytes: soluble,
slightly soluble, Weak) with calculations.
5. Factors affecting solubility.
6. Distribution phenomenon and application.
7. Colligative properties and lowering of vapor pressure.
8. Depression of freezing point, osmotic pressure.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.

3. 1. Definition of Solutions
• A solutions may be defined as a mixture of two or
more components that form a single phase which is
homogeneous down to the molecular level.
• The component that determines the phase of the
solution is termed the solvent and usually constitutes
the largest proportion of the system.
• The other components are termed solutes, and these
are dispersed as molecules or ions throughout the
solvent, i.e. they are said to be dissolved in the
solvent.
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Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
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4. Preparation of Solutions
• Write out the formula either from the prescription
(unofficial) or from an official text (official).
• Calculate the quantities required for each ingredient
in the formula to produce the required final volume.
• Remember, it is not usual to calculate for an overage
of product in the case of solutions as it is relatively
easy to transfer the entire final contents of the conical
measure.
• Also, as far as is practically possible, the product will
be assembled in the final measure, thus reducing any
transference losses.
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Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
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5. Types of solutions
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Tobruk, Libya.
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State of
Solvent
State of
Solute
State of
Solution
Examples
Gas Gas Gas Air, natural gas
Liquid Liquid Liquid Alcoholic beverages,
Antifreeze solution;
Liquid Solid Liquid Seawater, sugar solution
Liquid Gas Liquid Carbonated water (soda)
Ammonia solution;
Solid Solid Solid Metal alloys: brass, bronze,..
Solid Gas Solid Hydrogen in platinum

6. 2. Solvent-solute interaction
• Solubility depends on chemical, electrical &
structural effects that lead to mutual interactions
between the solute and the solvent.
• In pre or early formulation, selection of the most
suitable solvent is based on the principle of “like
dissolves like”.
• Polar solutes dissolve in polar solvents. Eg. Salts &
sugar dissolve in water .
• Non polar solutes dissolve in non polar solvents. Eg.
Naphtalene dissolves in benzene.
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Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
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7. Solvent- solute interaction
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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∆Hsoln = ∆H1 + ∆H2 + ∆H3

8. Thermodynamics of solvents
• The thermodynamic solubility of a drug in a solvent is
the maximum amount of the most stable crystalline
form that remains in solution in a given volume of the
solvent at a given temperature and pressure under
equilibrium conditions.
• The equilibrium involves a balance of the energy of
three interactions against each other: (1) solvent with
solvent, (2) solute with solute, and (3) solvent and
solute.
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Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
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9. 3. Solubility of gases in liquids
• The solubility of a gas in a liquid is the concentration
of the dissolved gas when it is in equilibrium with
some of the pure gas above the solution.
• Gases like hydrochloric acid, ammonia water, and
effervescent preparations containing carbon dioxide
that are dissolved and maintained in solution under
positive pressure.
• The solubility depends on the pressure, temperature,
presence of salts and chemical reactions.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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10. Solubility of liquids in liquids
• The components of an ideal solutions are miscible in
all proportions.
• Such complete miscibility is also observed in some
real binary systems, e.g. ethanol and water, under
normal conditions.
• In cases where partial miscibility occurs under
normal conditions the degree of miscibility is usually
dependent on the temperature.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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11. 4. Solubility of solids in liquids
• If two solids are either melted together and then
cooled or dissolved in a suitable solvents, which is
then removed by evaporation, the solid that is
redeposited from the melt or the solution will either
be a one-phase solid solution or a two-phase eutectic
mixture.
• In a solid solution, as in other types of solution, the
molecules of one component (the solute) are
dispersed molecularly throughout the other
component (the solvent).
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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12. 5. Factors affecting solubility
• Temperature
• Molecular structure of solute
• Nature of solvent: cosolvents
• Crystal characteristics: polymorphism and solvation
• Particle size of the solid
• Common ion effect
• Effect of indifferent electrolytes on the solubility product
• Effect of non-electrolytes on the solubility of electrolytes
• Effect of electrolytes on the solubility of non-electrolytes
• Complex formation
• Solubilizing agents
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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13. 6. Distribution phenomenon
and application
• If the substance is added to the immiscible solvents in
an amount insufficient to saturate the solutions, it will
still become distributed between the two layers in a
definite concentration ratio.
• If C1 and C2 are the equilibrium concentrations of
the substance in solvent 1 and solvent 2, the
equilibrium expression becomes
C1/C2 = K
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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14. Applications
• Effect of partition of ionic dissociation and molecular
association.
• Extraction.
• Solubility and partition coefficients.
• Preservative action of weak acids in oil-water
systems.
• Drug action and partition coefficients.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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15. 7. Colligative properties and
lowering of vapor pressure
• When a non-volatile solute is dissolved in a solvent,
certain properties of the resultant solution are largely
independent of the nature of the solute and are
determined by the concentration of solute particles.
• These properties are known as colligative properties
(Geek: collected together).
• The freezing point, boiling point, and osmotic
pressure of a solution also depend on the relative
proportion of the molecules of the solute and the
solvent.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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16. Lowering of vapor pressure
• It is more convenient to express the vapor pressure of
the solution in terms of the concentration of the
solute, rather than the mole fraction of the solvent.
• A solute lowers the vapor pressure of a solution in an
amount dependent on the mole fraction of the solute.
X1 = 1 - X2
• In which X1 is the mole fraction of the solvent and X2
is the mole fraction of the solute.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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17. 8. Depression of freezing
point
• The freezing point (or melting point) of a pure
compound is the temperature at which the solid and
liquid phases are in equilibrium under a pressure of 1
atmosphere (atm).
• The freezing point of a solution is the temperature at
which the solid phase of the pure solvent and the
liquid phase of the solution are in equilibrium under a
pressure of 1 atm.
• The amount of depression of the freezing point
depends on the molality of the solution.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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Depression of freezing
point

19. Osmotic pressure
• Osmosis is the process by which solvent molecules pass
through a semipermeable membrane (a barrier through
which only solvent molecules may pass) from a region of
dilute solution to one or more concentrated solution.
• The pressure that must be applied to the more
concentrated solution to prevent the flow of pure solvent
into the solution is known as the osmotic pressure.
• Solvent molecules move from a region where their
escape tendency is high to one where their escape
tendency is low.
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Faculty of Pharmacy, Omer Al-Mukhtar University,
Tobruk, Libya.
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Tobruk, Libya.
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Osmotic pressure

21. THANK YOUE-mail: nanjwadebk@gmail.com
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Faculty of Pharmacy, Omer Al-Mukhtar
University, Tobruk, Libya.
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