Question

So my chemistry class did a titration using EDTA and seawater. We were trying to determine the amount of calcium and magnesium in the water. We did two different runs one which told us the amount of ca+mg and one which told us the amount of ca only. I have the moleculare weights, the amount of EDTA used. How do I find the amount of Ca and the amount of Mg?

Answer 1

Hi thanks for your question.

For this calculation you have:

Then you can calculate first [Ca2+] using:

moles Ca²⁺ =moles EDTA =  molesEDTACa²⁺

gCa²⁺ = Molecular weight/mol x molCa²⁺

You can calculate [Mg²⁺] using:

molesCa²⁺ + molesMg²⁺ = molesEDTACa²⁺Mg²⁺

molesMg²⁺ = molesEDTACa²⁺Mg²⁺ -  molesEDTACa²⁺

gMg²⁺ = Molecular weight/mol x molMg²⁺