Question

21. determine the activity coefficient given the molal concentration of ZnBr₂ is 0.01 mol/kg.

Answer 1

For any aqueous solution of a salt:

The activity coefficient:

Where, I is the ionic strength of the solution

z₊ and z_- are the charges on the cation and anion respectively

Ionin Strength, I :

where m_i denotes the molality of the charged species i in the aqueous solution.

z_i is the valency of the charged species i in the aqueous solution

ZnBr₂ dissociates in aqueous solution to produce Zn²⁺ and 2 Br^- ions.

Balanced chemical reaction:

we see that 1 mole of ZnBr₂ dissociates to give 1 mole of Zn²⁺ and 2 moles of Br^- .

Therefore if the molality of ZnBr₂ is 0,01 molal , 1 molal of Zn²⁺ and 2 molal of Br^- is formed.

Note: number of moles of a species / kg of solution is the molality of the species.

Therefore, on substituting in ionic strength equation,

Activity co-efficient: