Question

The following quantities of salts were added to water to make a 1-liter solution:

1X10^-2 moles NaCl, 2X10^-2 moles CaCl2, 4.166 grams BaCl2

1. What is the ionic strength of the solution?

2. What is the activity of the Cl species?

Answer 1

(1)

Ionic strength I is a measure of total concentration of ions in solution.

So

Where

M_i = concentration of ion i in mol/lit

z_i = charge of ion i

So in this example

Nacl concentration in 1 lit of solution = 1X10-2 moles/lit given

So Concentration of Na⁺ and Cl^- are

CaCl₂ concentration = 2X10-2 mol/lit given

Here one mole of Ca²⁺ and 2 moles of Cl^- present.

So concentration of these ion

Third salt is BaCl₂ 4.166 grams given

So moles of BaCl₂

Molecular weight of BaCl₂ =208.23 gram/mol

Here also one ion of Ba²⁺ and 2 ion of Cl^- present.

So Concentration of ions

So according equation (1)

So ionic strength