Question

1. Why is the EDTA salt dried only at 80o C (i.e., why not 100o C)?

2. Suppose you did not heed our warnings and stored your EDTA solution in a conventional glass bottle (instead of a plastic bottle) -- how would this affect your final results (i.e., would they be high, low, or unchanged)? Explain.

3. Why is it not necessary that the plastic storage bottles be dry before transferring the EDTA for storage ?

4. Would the titration of Ca2+ with EDTA at a pH of 5 be feasible? Why or why not?

Answer 1

Answer no .1 EDTA salt dried only at 80^o C becuase On exposure to temperature above 100⁰ c the hydrate will slowly converted to anhydrous compounds.

Answer no 2. EDTA solution is stored in plastic bottles rather than glass bottles as glass metals may leach metal ions which would lower effective concentration .Glass will sometimes contain metal ions (soda glass, lead crystal...) which over a long period may react with the edta. It would be a very slow process, and assuming you're going to use the EDTA within a day or two it is unlikely to be an issue.

Answer no 3.

Plastic bottles contains nothing that will react with EDTA and there is no need to dry them before transferring EDTA for storage.

Answer no 4.

Titration at pH 5 is infeasible because there is no large inflection point in the curve near equivalnce point