Question

So, I have some questions about the analytical chemistry experiment "Titrations based on complex formation."
1- Can you determine Mg by displacement or back titration?
2- You need to know the amount of EDTA added to solution in back titration method but you do not need to know the amount of MgEDTA added in displacement titration. Why? Explain by giving related reactions.
3- What is the minimum pH value needed for satisfactory titrations of Ca+2 and Mg+2 cations with EDTA?

Thanks for your help.

Answer 1

1) Yes Mg can be determine by back/ displacement titration.In this case use Zn+2 solution for back/displacement titarion.

2) In back titration it is necessary to know the amount of EDTA to be added because in this case measure quantity of excess EDTA is to be added & excess EDTA is then determined using indiacator.

While in diplacement titration,No need to know the amount of Mg EDTA because in this case idea is only to make complex of Mg EDTA first then this Complex solution treated with cation (M⁺²) to be analyzed.then the liberated Mg+2 is then titrated with standard EDTA solution.

MgY^-2 + M⁺² MY² + Mg⁺²  where M⁺² is cation as analyte and MgY^-2 is Mg-EDTa complex

3) Minimum pH should be 10.Beacuse at low pH EDTA is insoluble in water as H4Y (4 -COOH group) is predominant in that pH (less than 2). With increasing the pH, each hydrogen ion in the carboxyl groups of EDTA will start to dissociate.At pH 10 all 4 -COOH groups completely dissociate to react fully.

EDTA