Effect of pH on the EDTA titration. Use Equation 12-11 to compute curves (pCa2+ versus mL of EDTA added) for the titration of 10.00 mL of 1.00 mM Ca2+ with 1.00 mM EDTA at pH 5.00, 6.00, 7.00, 8.00, and 9.00. Plot all curves on one graph and compare your results with Figure 12-10.

Titration of 10.0 mL of 1.0mM M2+ with 10 mM EDTA. The titration should be carried out at pH=5.00.

From eq 12-11 the equation for the fraction of titration of metal ion with EDTA is as follows

$\varphi =\frac{{\mathrm{C}}_{\mathrm{L}}{\mathrm{V}}_{\mathrm{L}}}{C_{\mathrm{M}}{\mathrm{V}}_{\mathrm{M}}}=\frac{1+{\mathrm{K}}_{\mathrm{f}}\mathrm{M}-{\displaystyle \frac{\left[\mathrm{M}\right]+{\mathrm{K}}_{\mathrm{f}}{\left[\mathrm{M}\right]}^2}{{\mathrm{C}}_{\mathrm{M}}}}}{{\mathrm{K}}_{\mathrm{f}}\mathrm{M}+\frac{\left[\mathrm{M}\right]+{\mathrm{K}}_{\mathrm{f}}{\left[\mathrm{M}\right]}^2}{{\mathrm{C}}_{\mathrm{L}}}}$

Other formulas need to be used

$\left[\mathrm{M}\right]={10}^{-\mathrm{pM}}$

Here instead of formation constant (Kf), conditional formation constant role="math" localid="1663431962376" $\left({\mathrm{K}}_{\mathrm{f}}\right)$should be taken in the above formula stated.

${\mathrm{K}}_{\mathrm{f}}={\mathrm{a}}_{{\mathrm{Y}}^4}{\mathrm{K}}_{\mathrm{f}}$

From table 12-1 the value of ${\mathrm{a}}_{{\mathrm{Y}}^4}$for EDTA at 250C, and pH 5 is 2.9×10-7

From table 12-1 the value of ${\mathrm{a}}_{{\mathrm{Y}}^4}$for EDTA at 250C, and pH 6 is 1.8×10-5

From table 12-1 the value of${\mathrm{a}}_{{\mathrm{Y}}^4}$for EDTA at 250C, and pH 7 is 3.8×10-4

From table 12-1 the value of${\mathrm{a}}_{{\mathrm{Y}}^4}$for EDTA at 250C, and pH 8 is 4.2×10-3

From table 12-1 the value of${\mathrm{a}}_{{\mathrm{Y}}^4}$for EDTA at 250C, and pH 9 is 0.041

From table 12-2 we get log Kf for Ca2+= 10.65

The curve for the metal Ca at different pH is shown below