Re: How do you Determine Calcium Hardness in water with EDTA titration?

This is a summary of what you can find in " Standard methods for Examination 
of
water and wastewater
Principle :
when EDTA is added to water containing both Calcium and Magnesium it 
combines
firstly wityh calcium. Calcium can be determined directly with EDTA when the 
pH
is made sufficiently high that the magnesium is largely precipitated as the
hydroxide and an indicator is used that combines to with calcium only. 
Several
indicators give a color change when all of the calcium has been complexed by
EDTA at a pH of 12 to 13.

Reageant
solution NaOH 1N;
Indicator= murexide (ammonium purpurate) or Eriochrome Blue Black R.
EDTA: standard EDTA titrant 0.001M.
Sample: 50mL.

Procedure:
Add 2mL NaOH solution 1N , Add 0.È g indicator mixture , add EDTA titrant
slowly with continuous steering to the proper end point.
Best regards.


Jacques SIBONY