Ionic Equilibrium

The ionic strength

I

of a solution is given by:

I%20%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Csum_i%20c_i%20z_i%5E2%2C

where

c_i

is the concentration of the

i

-th ion and

z_i

is the charge of the

i

-th ion. Given:
-

%5Ctext%7BNa%7D%5E%2B

has a concentration of 0.25 M and a charge of 1,
-

%5Ctext%7BCa%7D%5E%7B2%2B%7D

has a concentration of 0.12 M and a charge of 2,
-

%5Ctext%7BCl%7D%5E-

has a concentration of 0.32 M and a charge of -1,
-

%5Ctext%7BHCO%7D_3%5E-

has a concentration of 0.05 M and a charge of -1.
Substitute the values:

I%20%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Cleft(%200.25%20%5Ctimes%201%5E2%20%2B%200.12%20%5Ctimes%202%5E2%20%2B%200.32%20%5Ctimes%201%5E2%20%2B%200.05%20%5Ctimes%201%5E2%20%5Cright)%0A%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Cleft(%200.25%20%2B%200.48%20%2B%200.32%20%2B%200.05%20%5Cright)%0A%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%201.10%20%3D%200.55%20%5C%2C%20%5Ctext%7BM%7D.

Thus, the ionic strength of the water sample is

0.55%20%5C%2C%20%5Ctext%7BM%7D

Chapter Questions
1 MCQs