# Titration with EDTA and Eriochrome black T

I have a titration of Calcium Ions with EDTA. When I reach a volume of 9.6mL I the liquid turns slightly blue and after that the more I add the bluer it becomes. Now at what point is my titration finished? When I notice the first change or as soon as adding more EDTA doesnt change the color?

• Suggestion: Prepare a stem solution (i.e. of known $c(\ce{Ca^{2+}}$). Perform the titration several times. Once "as if you were unaware about $c(\ce{Ca^{2+}}$" till the point all Calcium is chelated (which may be, taking known concentration of your stem solution and its volume, calculated in advance). Keep a small amount of this solution, for example in a test tube. Repeat the titration, intentionally adding more EDTA solution, than necessary; equally keep some of this solution as visual reference in a test tube. Now perform a titration with your unknown, with the visual aides beside. Apr 22, 2017 at 12:23