2. Definition:-
• SOLUBILITY
“ it is ability of one substance to fully dissolved in another substance
under specified condition.”
“ The concentration of a substance (solute) that dissolves in a given
volume of solvent at a certain temperature to form a homogenous
solution.”
“ The spontaneous interaction of two or more substances to form a
homogenous molecular dispersion.”
Types of Solubility:-
1) Intrinsic Solubility
2) Apparent Solubility
3. • Solute: a component which dissolved in the solvent, present in less
amount in the solution.
• Solvent: a component in which solute is dissolved, present in more
amount than solute.
• Solution: A system in which solutes are completely dissolved in
solvent & form a homogenous molecular dispersion.
• Saturated solution: Solution in which the solute in solution is in
equilibrium with solid phase.
• Unsaturated solution/ sub-saturated solution : Solution
containing dissolved solute in concentration below that necessary
for complete saturation.
• Supersaturated solution: Solution containing more of the
dissolved solute than it would normally contain.
4. 1. Saturated Solution - holds the maximum amount of solute
2. Unsaturated Solution – holds less than the maximum amount of
solute
3. Supersaturated Solution – holds more than the maximum
amount of solute
7. Mechanism of Solute solvent interaction
Steps of solid going into
solution.
1. Step 1: Hole open in the
solvent
2. Step 2: One molecule of
the solid breaks away from
the bulk
3. Step 3: The solid molecule
is enter into the hole in the
solvent
9. • If the solvent is A & the solute is B, and the forces of attraction are represented
by A-A, B-B and A-B,
• One of the following conditions will occur:
1. If A-A >> A-B The solvent molecules will be attracted to each other & the solute will
be excluded. Example: Benzene & water, where benzene molecules are unable to
penetrate the closely bound water aggregates.
2. If B-B >> A-A The solvent will not be able to break the binding forces between
solute molecules. Example NaCl in benzene, where the NaCl crystal is held by
strong electrovalent forces which cannot be broken by benzene.
3. If A-B >> A-A or B-B, or the three forces are equal The solute will Form a solution.
Example: NaCl in water.
10. Solvation / Dissolution
• “ Interaction of a solute with the solvent, which leads to
stabilization of solute species by surrounding it with
solvent in the solution”
• +ve solvation energy= endothermic dissolution
• -ve solvation energy= exothermic dissolution
11. • Solvation process affected by hydrogen bonding and van der
Waals force
• Kinetic process and rearranging solvent –solute mole. Into
solvation complex to distribute solute mole. within the solvent
• Insoluble solute mole. Interaction solute mole. Break parts
Solvation ( ion exchanges) by the solvent
• Solvants :-
a compound that froms between a solute and its solvent
• Hydrates:-
( ammoniates, alcoholates,etherates)
• Solvation number:-
(mol/l,mg/ml)
12. Association
“ Chemical reaction in which the opposite electric charge ions come
together in solution & form a distinct chemical entity”
• Classification according to nature of interaction:
1. Contact
2. Solvent shared/Solvent separated
3. Fully solvated
15. Polar solvents
• The solubility of a drug is due in large measure to the polarity of the solvent,
that is, to its dipole moment. Polar solvents dissolve ionic solutes and other
polar substances.
• The ability of the solute to form hydrogen bonds is a far more significant
factor than is the polarity as reflected in a high dipole moment
• Water dissolves phenols, alcohols and other oxygen & nitrogen containing
compounds that can form hydrogen bonds with water.
• The solubility of a substance also depends on structural features such as the
ratio of the polar to the nonpolar groups of the molecule.
• As the length of a nonpolar chain of an aliphatic alcohol increases, the
solubility of the compound in water decreases
• Straight-chain monohydroxy alcohols, aldehydes, ketones, and acids with
more than four or five carbons cannot enter into the hydrogenbonded structure
of water and hence are only slightly soluble.
16. • Hydrogen bonding is the attractive
interaction of a hydrogen atom with an
electronegative atom, such as nitrogen,
oxygen
Dipole-dipole forces are electrostatic interactions of permanent
dipoles in molecules.
17. Non polar solvents
• Non-polar solvents are unable to reduce the attraction
between the ions of strong and weak electrolytes because
of the solvents' low dielectric constants.
• They are unable to form hydrogen bonds with non
electrolytes.
• Non polar solvents can dissolve non polar solutes through
weak van der Waals forces
• Example: solutions of oils & fats in carbon
tetrachloride or benzene.
• Polyethylene glycol 400
• Castor oil
18. Semi polar solvents
• Semi polar solvents, such as ketones can induce a certain degree
of polarity in non polar solvent molecules.
• For example, benzene, which is readily polarizable, becomes
soluble in alcohol
• They can act as intermediate solvents to bring about
miscibility of polar & non polar liquids.
• Example: acetone increases solubility of ether in water.
• Propylene glycol has been shown to increase the mutual
solubility of
• water and peppermint oil and of water and benzyl benzoate
20. FACTORS INFLUENCING SOLUBILITY
• 1. Temperature
• 2. Nature of solvent ( like dissolves like)
• 3. Pressure
• 4. pH
• 5. Particle size
• 6. Crystal structure
• 7. Molecular structure
• 8. Solute- solvent interactions
• 9. Addition of substituent
• 10. Common ion effect
• 11. Solubilizing agents
21. SOLUBILITY OF LIQUIDS IN LIQUIDS
• 1. Completely miscible liquids:
E.g. Water+ ethanol, Glycerine+ Alcohol, benzene+
CCL4
• 2. Partially miscible liquids:
E.g. Phenol+ water.
• 3. Completely immiscible liquids:
E.g. Mercury+ water.
22. • RAOULT’S LAW
• “The partial pressure (Pi) of each component in a solution is equal to the mole
fraction of the component & the vapour pressure of the pure component”
Pi = xP
Or
P = pAxA + pBxB
IDEAL SOLUTIONS
“ Solutions which obey Raoult’s law
in all the solute composition in a
solvent”
23. • REAL/ NON IDEAL SOLUTIONS
• “Solutions which do not obey Raoult’s law
over entire range of composition”
Negative deviation
PA < Xa P
△H < 0
△V < 0
Positive deviation
PA > Xa P
△H > 0
△V > 0
24. SOLUBILITY OF GASES IN LIQUIDS
• Henry’s law:
‘Solubility is directly proportional to partial
pressure of gas at a constant temperature’.
S= KP
25. Factors affecting gas in liquids
• Effect of pressure
• Effect of temperature
• Effect of electrolytes and non electrolytes
• Effect of chemical reaction
26. NERNS’T DISTRIBUTION LAW
( PARTITION COEFFICIENT)
• “ If a solute distributes between two immiscible solvents
at a constant temperature then the ratio of its
concentration in two solvents is a constant value”.
• K= C1/ C2
28. • •water soluble drug (ionized or polar) is readily
absorbed via aqueous channels or pores in cell
membrane.
• •Lipid soluble drug (nonionized or non polar) is
readily absorbed via cell membrane itself.
