Debye- Hückel Theory of Electrolytes

Debye- Hückel  Theory of Electrolytes

Assumptions

i) Electrolytes are completely dissociated into ions into solutions

ii) The solutions are dilute, with a concentration of 0.01 m or lower

iii) on average, each ion is surrounded by ions of opposite charge, forming an ionic atmosphere.

Because γ+ nor γ- could be measured directly, the final result is expressed in terms of the mean ionic activity coefficient of the electrolyte  as follows

logγ± = -0.509 z₊z_√I                                                                            (34)

This equation is known as the Debye-Hückel limiting law

where     signs denote the magnitude but not the signs of the product z+z-.

The quantity I called the ionic strength, is defined as follows

                                                                                   (35)

where mi and zi are the molality and charge of the ith ion in the electrolyte respectively

Exercise 6

Calculate the mean activity coefficient (γ_±) of a 0.01m aqueous solution of CuSO₄ at 298K.