EDTA Titration for water hardness

[positron]

In order to determine the quantity of Ca and Mg ions in a water sample, it requires a titration with EDTA solution.

 

The procedure also asks that the pH of the reaction be kept at a basic range of 8-10 as all reactions between metal ions and EDTA are pH dependent, and for divalent ions, solutions must be kept basic (and buffered) for the reaction to go to completion.

 

My question is: If the buffer was omitted, would the quantity of EDTA required br higher or lower that if the buffer was added?

[Tartaglia]

at ph 10 edta is a 4 negative ion and can act as a hexadentate ligand with the two amine groups and the four carboxylate ions acting as e- pair donors. If edta were added unbuffered it would be some sort of zwitterion or possibly a dizwitterion. This would block hexadentate coordination and probably lead to formation of polymeric metal ligand metal ligand chains, or possibly little coordination as the entropy consideration will be a lot less favourable