How to convert PPM to Mol/Litre

Question

For example, if you have 20 ppm of Iron(III) standard solution, how do you convert this into mol/litre?

Answer 1

ppm  = mg/lt

g/mol.wt =  moles.  thus convert mg into g and then moles and with this get mol/lt.

Answer 2

You are looking for a conversion between a very dilute solution, (ppm) and a concentrated solution. It is easy to remember that ppm = mg/litre. Work from there. If you have 20ppm Fe, then you have 20mg Fe in 1 litre.

Atomic mass Fe = 55.845g, therefore the molarity will be:

0.020/55.845 = 3.58*10^-4moles/litre