Question

1. What is the ionic strength of a solution composed of 0.M NaCl and 0.2M Na2SO4?

Answer 1

$NaCl \rightarrow Na^++Cl^-$

Let concentration of NCl is 0.1 M

Then concentration of Na⁺ is 0.1 M

And consideration of Cl^- is 0.1 M

$Na_2SO_4 \rightarrow 2Na^++SO_4^{2-}$

If concentration of $Na_2SO_4$ is 0.2 M,

Then concentration of Na⁺ is 0.2x2=0.4 M

And consideration of $SO_4^{2-}$ is 0.2 M

If we have 1 l of this solution total concentration of Na⁺ is 0.1+0.4=0.5M

$I=0.5\sum c(z)^2=0.5(0.5(1)^2+0.1(-1)^2+0.2(-2)^2)=0.7 M$