Question

Why is it necessary to standardize solutions of `"EDTA"` in complexometric titrations?

Answer 1

Why is it necessary to standardize any primary standard?

Explanation:

In a titration reaction, typically (i) a KNOWN volume of titrant, of (ii) known concentration, is added to an unknown quantity of reactant. Without knowledge of (i) or (ii), the analyst cannot determine molar equivalence.

In other words, you are performing the following reaction:

`"Metal ion " + " EDTA"rarr" (Metal ion)"*"EDTA"`.

Since `"[Metal ion]"^+` is unknown, you can make no measurement of the amount present, unless you know `"[EDTA]"` fairly accurately. And thus a known mass of primary standard is required to standardize, to calibrate the titration.

Is this clear?