|MadSci Network: Chemistry|
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
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