In forming a chelate with a metal ion, a mixture of free EDTA (abbreviated Y4?)
ID: 775348 • Letter: I
Question
In forming a chelate with a metal ion, a mixture of free EDTA (abbreviated Y4?) and metal chelate (abbreviated MYn?4) can buffer the free metal ion concentration at values near the dissociation constant of the metal chelate, just as a weak acid and a salt can buffer the hydrogen ion concentration at values near the acid dissociation constant. This equilibrium is governed by the equation where Kf is the association constant of the metal and Y4?, ?Y4? is the fraction of EDTA in the Y4? form, and [EDTA] is the total concentration of free (unbound) EDTA. K 'f is the "conditional formation constant." How many grams of Na2EDTA?2H2O (FM 372.23) should be added to 1.94 g of Mg(NO3)2?2H2O (FM 184.35) in a 500-mL volumetric flask to give a buffer with pMg2 = 8.00 at pH 10.00? (log Kf for Mg-EDTA is 8.79 and ?Y4? at pH 10.00 is 0.30.)
Explanation / Answer
Hi,
[MgY2+] = 1.94g/ (184.35g/mol) X 0.5L = 0.02105 M
Given that: log Kf for Mg-EDTA is 8.79 and alphaY4