# Ionic Strength

1. Nov 26, 2007

### higherme

Calculate the ionic strength of Ca2+ in a 0.01M CaCO3 solution.

equation to use is:

u=0.5 sum(Mi)(zi)^2
where M is the concentration and z is the charge of the species

my question is when I am calculating the ionic strength of Ca2+, do I have to include
CO3^2- that is in that solution?

so, it would be :

U=0.5 (0.01M Ca2+)(2+)^2 + (0.01M CO3^2-)(2-)^2
U=0.04M

if I don't include:
U=0.5 (0.01M Ca2+)(2+)^2
U=0.02M

2. Nov 27, 2007

### Gokul43201

Staff Emeritus
The question is meaningless to me. The ionic strength is defined for the entire solution, not for individual species.

As meaningless as it may be, it appears that the questioner whats you to calculate the contribution of Ca2+ alone (your second calculation). But this is just my interpretation of intent.

If you get a chance, please inform the person that wrote this question that ionic strength is not defined for individual species. If this is from a book, please cite the title, author, edition and page number.