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My titration of calcium oxalate with NaEDTA doesn't work. I need to calculate the ion calcium within my sample. My essay is to test anticalculi activity.

Why do I say I have problem? Because the colour keeps turning back to its initial colour (pink) more than twelve times. It's never ending and the titration end point is so premature.

In my preparation, I added HCl 0.5 M to my calcium oxalate so it dissolves. Calcium oxalate has very low solubility.

  • First, I used EBT indicator and ammonia buffer. When i add the ammonia the solution became foggy and there's a precipitation within the sample.
  • So I used substitution titration with Mg-EDTA (EBT indicator) = Still happens
  • Then change the indicator to hydroxynaftol blue and calcon = Still happens (I don't use buffer with this indicator, only NaOH, but when I add NaOH it's became foggy again)
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Does it have to be complexometric?

You could acidify the sample and do a redox titration of the oxalate with permanganate or dichromate. And since the amount of oxalate is the same as calcium, bob's your uncle.

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