in complexometric titration of MgSO4 by EDTA, why we add amonia amonium chloride (NH3.NH4Cl) ?

Answer 1

NH3.NH4CL acts as a buffer to adjust PH of the solution to obtain Finally Mg-complex(EDTA).

Answer 2

I agree with the answer above and would like to add that if not adding the buffer solution (amonia and amonium chloride), the EDTA (which is actually Na4EDTA) will hydrolize and the solution would become very rich in HO(-) :

EDTA(4-) + H20 <=> HEDTA(3-) + HO(-)

Answer 3

The equation of the process is below:
(Mg2+) + (Y4-) = MgY2- , where Y4- is the anion of EDTA.
This complexonometric reagent makes complexes with cations of metals only in the form of Y4-. The molar concentration of this anion is dependent on the total concentration of EDTA and also on pH and is given by a very long mathematic equation. To determine the equilibrium point of this titration we need to keep pH on a non-changing level, and an ammonia buffer system will certainly help us :)

Answer 4

I believe that the ammonia and ammonium chloride are functioning as a buffer to keep the pH at a certain level. If the pH in the solution is too high, Mg2+ ions will precipitate as magnisium hydroxide.

Answer 5

to solvate the amonia and isolate the particle diatribelates