Factors affecting solubility:-
The solubility depends on the physical form of the solid, the nature and composition of solvent medium as well as temperature and pressure of system.
Particle Size
The
size of the solid particle influences the solubility because as a particle
becomes smaller, the surface area to volume ratio increases. The larger surface
area allows a greater interaction with the solvent. The effect of particle size
on solubility can be described by
Sis
the solubility of infinitely large particles
Sis
the solubility of fine particles
V
is molar volume
g
is the surface tension of the solid
r
is the radius of the fine particle
Temperature
Temperature
will affect solubility. If the solution process absorbs energy then the
solubility will be increased as the temperature is increased. If the solution
process releases energy then the solubility will decrease with increasing
temperature. Generally, an increase in the temperature of the solution
increases the solubility of a solid solute. A few solid solutes are less
soluble in warm solutions. For all gases, solubility decreases as the
temperature of the solution increases.
Pressure
For
gaseous solutes, an increase in pressure increases solubility and a decrease in
pressure decrease the solubility. For solids and liquid solutes, changes in
pressure have practically no effect on solubility.
Nature of the solute and solvent
While
only 1 gram of lead (II) chloride can be dissolved in 100 grams of water at
room temperature, 200 grams of zinc chloride can be dissolved. The great
difference in the solubilities of these two substances is the result of
differences in their natures.
Molecular size
Molecular
size will affect the solubility. The larger the molecule or the higher its
molecular weight the less soluble the substance. Larger molecules are more
difficult to surround with solvent molecules in order to solvate the substance.
In the case of organic compounds the amount of carbon branching will increase
the solubility since more branching will reduce the size (or volume) of the
molecule and make it easier to solvate the molecules with solvent.
Polarity
Polarity
of the solute and solvent molecules will affect the solubility. Generally
non-polar solute molecules will dissolve in non-polar solvents and polar solute
molecules will dissolve in polar solvents. The polar solute molecules have a
positive and a negative end to the molecule. If the solvent molecule is also
polar, then positive ends of solvent molecules will attract negative ends of
solute molecules. This is a type of intermolecular force known as dipole-dipole
interaction. All molecules also have a type of intermolecular force much weaker
than the other forces called London Dispersion forces where the positive nuclei
of the atoms of the solute molecule will attract the negative electrons of the
atoms of a solvent molecule. This gives the non-polar solvent a chance to
solvate the solute molecules.
Polymorphs
A
solid has a rigid form and a definite shape. The shape or habit of a crystal of
a given substance may vary but the angles between the faces are always
constant. A crystal is made up of atoms, ions, or molecules in a regular
geometric arrangement or lattice constantly repeated in three dimensions. This
repeating pattern is known as the unit cell.The capacity for a substance to
crystallize in more than one crystalline form is polymorphism. It is possible
that all crystals can crystallize in different forms or polymorphs. If the
change from one polymorph to another is reversible, the process is called
enantiotropic. If the system is monotropic, there is a transition point above
the melting points of both polymorphs. The two polymorphs cannot be converted
from one another without undergoing a phase transition. Polymorphs can vary in
melting point. Since the melting point of the solid is related to solubility,
so polymorphs will have different solubilities3. Generally the range of
solubility differences between different polymorphs is only 2-3 folds due to
relatively small differences in free energy.
https://amzn.to/2vPBYyu
Authored by
S.M.Imroz , M.Pharm(Pharmaceutics) .,
Factors affecting solubility Pdf
Authored by
S.M.Imroz , M.Pharm(Pharmaceutics) .,
Factors affecting solubility Pdf
REFERENCES-
1. Adam M. Persky and Jeffrey A. Hughes, Solutions and
Solubility. http://www.cop.ufl.edu/safezone/prokai/pha5100/pha5110.htm
2. Solubility, From Wikipedia, the free encyclopedia.
Retrieved from http://en.wikipedia.org/wiki/Solubility
3. Indian Pharmacopoeia, Ministry of Health and family
welfare, Government of India, Published by the controller of publications,
Delhi, 1996, 1, 7.
4. James K., “Solubility and related properties”, vol.
28, Marcel Dekker Inc., Newyork, 986, 127 –146, 355 – 395.
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4 comments
Click here for commentsIt is my understanding that particle size DOES NOT influence solubility. Particle size can influence dissolution rate, but the same amount of drug will dissolve regardless of whether you have large particles or small particles.
ReplyRead full Pressure Class 10| SEE Physics Notes
ReplyWe had this topic in the subject of Chemistry. This is my favorite part of Chemistry - particles and molecules.
ReplyYou can influence the dissolution rate, but the same amount of drug will dissolve regardless of whether you have large particles or small particles.
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