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.

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