[new2007]

Hi, I was just wondering if you could help me with this question. I'd like to know why the EBT indicator reaction has to happen after the free Calcium and magnesium reactions react. if the indicator reaction occured before this point, what would happen? does this have to do with the stability of the EBT complexes or how sharp the end point will be? thanks

[Borek]

I'd like to know why the EBT indicator reaction has to happen after the free Calcium and magnesium reactions react.

Why it has to happen or why it happens? It has to happen to let you determine titration endpoint, it happens because stability of calcium/magnesium EBT complexes are lower than stability of EDTA calcium/magnesium complexes.

if the indicator reaction occured before this point, what would happen?

Will you determine endpoint correctly then?