Dielectric Constant

Dielectric Constant:

·         It is the ratio of energy requires for separating two charges in solvent and vacuum respectively.

·         Substance has capacity to produce dipole in another molecule, dielectric constant is a measure of this capacity.

·         It is affected by both the attractive forces that exist between atoms and also molecules.

What is dielectric constant?

·         Kept two charges (Na⁺& CL^-) with solvent (H₂O)

·         Let us take Xamount of energy that required to separate the charges (Na⁺& CL^-) in given solvent (H₂O).

·         Now provide vacuum between them (Na⁺& CL^-) instead of solvent (H₂O) medium.

·         In this Y amount of energy that required to separate charges.

·         So, as per definition;

·        

·         Here Y is consider as 1 because it is not change for ion

·         Then example of water taken,

o   Water have dielectric constant of = 78.5

·         So, that means amount of energy required to separate two charges in water is, 78.5 times more than the energy required in vacuum.

Calculation of dielectric constant:

·         Measure the conductance between the two plates, whene keeping the test solution in between plates.

·         After that measure the conductance in vacuum.

·         Ratio of conductance gives dielectric constant

Effect on solubility:

·         Water is a dipolar substance.

·         Drugs may be polar or semipolar.

·         The water by either attracting or repelling the electrons, will induce a small charge in the non-polar drug molecules whenever there are mixed with water.

·         So this leads toproduction of induced dipoles; because of which the solubility increases.

·         Hence we can conclude that dielectric constant value of solvent is increase, then solubility also increase because,

As per concept of dielectric constant; Substance has capacity to produce dipole in another molecule, dielectric constant is a measure of this capacity.