I finished the DETERMINATION OF Ca BY COMPLEXOMETRIC TITRATION WITH EDTA lab and

Question

I finished the DETERMINATION OF Ca BY COMPLEXOMETRIC TITRATION WITH EDTA lab and there are some questions I dont understand.

Ethylenediaminetetraacetic acid (EDTA) is a remarkable chelating agent that will form a 1:1 complex with just about any metal cation. In this experiment, you will determine the weight percent of Calcium oxide (CaO) in an unknown sample by complexometric titration with EDTA.

my questions are

1. Why is it important (no. . . imperative) that one use de-ionized water in this experiment?

2. What kinds of error can be introduced by using an indicator that changes from one color to another as opposed to one like phenolphthalein, which changes from clear to pink?

Explanation / Answer

1. It is important to use de-ionized water in this experiment because in this experiment calmagite indicator is used. Calmagite indicator is used in this titration because it is an excellent indicator for calcium and magnesium. Calmagite forms very strong complexes with many transition metals and therefore even traces of these metals may be enough to retain the indicator in the red form. Very pure (deionized) water must be used for titrations in which calmagite is used as indicator to prevent this problem.

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