Tonicity, Isotonic solutions, Hypotonic solutions, Hypertonic solutions, Interface, Surface, Absorption, Adsorption, Surface tension, Solubilization, Polymorphism
Tonicity:
Tonicity is
measure of the osmotic pressure of two solutions separated by a semi permeable
membrane.
Isotonic solutions:
Two solutions
are said to be iso-osmotic or isotonic if they exert the same osmotic pressure
when separated by a semi permeable membrane.
Example: 0.9 %
solutions of NaCl is said to be isotonic solutions.
Hypotonic solutions:
Solutions with
osmotic pressure lower than that of the body fluids or of 0.9% NaCl solution
are called hypotonic solution.
Hypertonic solutions:
Those solutions
having a higher osmotic pressure than the body fluids or of 0.9% NaCl solutions
are called hypertonic solution.
Interface:
The boundary
between two phases is generally described as an interface.
Surface:
When one of the
phases is a gas or a vapor and the other a liquid or solid, the outer space of
the phases which is contacted or exposed with the outer space of other phases
is called surface of that phase.
Absorption:
Absorption is
the incorporation of a substance in one state into another of a different
state.
Adsorption:
Adsorption is
the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or
dissolved solid particles to a surface.
Surface tension
is a property of the surface of a liquid that allows it to resist an external
force.
Solubilization:
The process by
which water insoluble or partly soluble substances are brought into aqueous
solution by incorporation into micelles is termed as solubilization.
Polymorphism:
Polymorphism is
the ability of a compound(or element) to crystallize as more than one distinct
crystalline species with different internal lattices.
Polymorphism (or
crystal polymorphism) is a phenomenon related to the solid state; it is the
ability of a compound in the solid state to exist in different crystalline forms
having the same chemical composition. Substances that exist in a non-crystalline
solid state are said to be amorphous.
Rate of reaction, Zero Order Reaction, First order reaction, Second order reaction
Rate of reaction:
The rate of a
chemical reaction is defined as the velocity with which a reactant or reactants
undergo chemical change.
Zero Order Reaction:
If the rate of a
reaction is independent of the concentration of the reacting species, the
reaction is said to be a zero-order reaction.
First order reaction:
A first order
reaction is one where the rate depends on the concentration of the species to the first power.
Second order reaction:
A second order reaction is one where the rate
depends on the concentration of the species to the second power. Buffer solutions, Buffer action, Buffer capacity, Factors affecting pH of Buffer Solutions, Biological buffers, Pharmaceutical Buffers
Buffer solutions:
Buffer solutions
are solutions of compounds or mixtures of compounds which resist change in
their pH upon addition of small quantities of an acid or alkali.
Buffer action:
The ability of
certain solutions to resist change in their pH upon addition of an acid or a
base is known as the “Buffer action”
Buffer capacity:
The buffer
capacity of a solution is a measure of its magnitude of resistance to change in
pH on addition of an acid or base. It is also referred to as buffer index,
buffer efficiency, buffer coefficient or buffer value.
ΔΒ
β =
--------------
ΔpH
β = Buffer Capacity
ΔΒ = Small increment in gram equivalent
per liter of strong base (or acid).
ΔpH
= Small change of pH.
Factors affecting pH of Buffer Solutions:-
The pH of a
buffer solution may be affected by
Ø Fluctuation in
the temperature
Ø Its dilution
with a solvent.
Ø The addition of
a neutral salt.
Biological buffers:
Ø The pH of blood
is maintained at about 7.4 with a range of 7.0 to 8.0.
Ø The pH of
lacrimal fluid or tears is about 7.4 with a range of 7.0 to 8.0. Tears degree
of buffer capacity with pH value between 3.5 and 10.5 can usually be tolerated
with little discomfort.
Ø The average pH
of urine is about 6.0 with a range of 4.5 to 7.8.
Pharmaceutical Buffers:
1.
Buffers
in tablet formulation:-
Ø Sodium
bicarbonate
Ø Magnesium
carbonate
Ø Sodium citrate
2.
Buffers
in ophthalmic preparation:-
Ø Clude borate
Ø Phosphate and
carbonate buffers.
3.
Buffers
in parenteral preparations:-
Ø Acetate buffers
Ø Phosphate
buffers
Ø Citrate buffers
Ø Glutamate buffers
4.
Buffers
in creams and ointments:-
Ø Citric acid and
its salts.
Ø Phosphoric acid
and its salts.
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