--%>

What is solvent dielectric effect? Explain with equation.

Ionic dissociation depends on the dielectric constant of the solvent.

The Arrhenius that ions are in aqueous solutions in equilibrium with parent molecular species allows many of the properties of ionic solutions to be understood. But difficulties began to arise after the initial acceptance of this ionic solution is to be understood. Ultimately the Arrhenius theory was attacked for the postulating molecules instead of ions in solutions of strong electrolytes. This was a dramatic reversal of the initial attacks on the Arrhenius theory which criticized it for postulating ions instead of undissolved molecules.

Refinements to the simplest ideas of the ionic solutions depend on the recognition of the role of the solvent and on the effect of interactions between the ions. 

A remarkable feature of the Arrhenius electrolytic dissociation theory is that although it attributes the dissociation process to the solution of the electrolyte, it proceeds to ignore the role of the solvent. It treats the solvent as if it were an inert, ignorable medium. A detailed understanding of the molecular nature of ionic solutions must involve the very important role played by the solvent. It is necessary, for instance, to understand why water is a unique solvent for ionic systems.

The electrostatic force of attraction between ions of charge Z+ and Z- is given by Coulomb's law:

For vacuum: ƒ(r) = Z+Z-[e2/4∏ε0)]/r2

For medium of dielectric ε/ε0: ƒ(r) = Z+Z-[e2/4∏ε0)]/(ε/ε0)r2

With the numerical values for e2/4∏ε0, the second of this equation is:

ƒ (r) = (2.307 × 10-28) Z+Z-/(ε/ε0)r2

For water, the dielectric constant factor ε/ε0 has the very large value of about 80. The force of interaction and the energy required to overcome coulombic forces are thus smaller by almost of very low dielectric. The easy dissociation of electrolytes in aqueous solutions compared with gaseous or low phase dielectric material is therefore understandable in terms of the high dielectric constant of water. The initial criticisms raised against the Arrhenius theory for postulating the dissociation of electrolysis in solution, however, remain valid arguments against any theory postulating appreciable dissociation to form free ions insolvents of low dielectric constant.

Although the dielectric effect is a major factor for the formation of ionic species in aqueous solutions, it is not great enough to reduce the intermolecular interaction to the small values found for gas phase molecules. We must therefore produce that for all but extremely dilute solutions, ionic interactions will not produce behavior found at infinite dilutes.

929_solvent dielectric.png 
A similar treatment of the activities themselves leads, again for one to one electrolytes, to the mean activity 1285_solvent dielectric1.png

Extension of this property lets activities and their coefficients be defined for electrolytes beyond the AB type. An AB2 electrolyte would dissociate according to 

AB2 = A2+ + 2B-

And the activity term that would appear in all thermodynamic treatments would be of form:

(aA2+) (aB-)2

   Related Questions in Chemistry

  • Q : Basic concept Give me answer of this

    Give me answer of this question. The volume of water to be added to 100cm3 of 0.5 N N H2SO4 to get decinormal concentration is : (a) 400 cm3 (b) 500cm3 (c) 450cm3 (d)100cm3

  • Q : Basic concepts Determination of correct

    Determination of correct mol. Mass from Roult's law is applicable to :

  • Q : Question 6 A student was analyzing an

    A student was analyzing an unknown containing only Group IV cations. When the unknown was treated with 3M (NH4)2CO3 solution, a white precipitate formed. Because the acetic acid bottle was empty, the student used 6M HCl to dissolve the precipitate. Following the procedure of this experiment, the stu

  • Q : What do you mean by the term enzymes

    What do you mean by the term enzymes? Briefly illustrate it.

  • Q : Neutralisation of phosphorous acids

    Provide solution of this question. To neutralise completely 20 mL of 0.1 M aqueous solution of phosphorous acid (H3 PO3) the volume of 0.1 M aqueous KOH solution required is: (a) 40 mL (b) 20 mL (c) 10 mL (d) 60 mL

  • Q : Calculating amount of Sodium hydroxide

    Choose the right answer from following. The amount of NaOH in gms in 250cm3 of a0.100M NaOH solution would be : (a) 4 gm (b) 2 gm (c) 1 gm (d) 2.5 gm

  • Q : Base parachloroaniline is strong base

    parachloroaniline is strong base than paranitroaniline

  • Q : Analytical chemistry 37% weight of HCl

    37% weight of HCl and density is 1.1g/ml. find molarity of HCl

  • Q : Chem Silicon has three naturally

    Silicon has three naturally occurring isotopes. 28Si, mass = 27.976927; 29Si, mass = 28.976495; 30Si, mass = 29.973770 and 3.10% abundance. What is the abundance of 28Si?

  • Q : Molecular Symmetry Types The number of

    The number of molecular orbitals and molecular motions of each symmetry type can be deduced. Let us continue to use the C2v point group and the H2O molecule to illustrate how the procedure develop