91Ó°ÊÓ

Consider the titration of 50.0 mL of 1.00 × 10^-3 M Zn²⁺ with 1.00 × 10^-3 M EDTA at

pH 10.00 in the presence of 0.10 M NH₃. The equivalence point is at 50.0 mL

Equations and data obtained in order to proceed for calculation are as follows

${\mathrm{Î\pm }}_{Z{n}^{2+}}=\frac{1}{1+{\mathrm{β}}_{1}L+{\mathrm{β}}_2{L}^2+{\mathrm{β}}_3{L}^3+{\mathrm{β}}_4{L}^4}$

From Eq 12-17${\mathrm{Î\pm }}_{Z{n}^{2+}}=1.8×{10}^{-5}$

$$\begin{gathered} K_f={10}^{16.5} \\ \mathrm{At}\mathrm{pH}10{\mathrm{Î\pm }}_{Y^{4-}}=0.3(Table12-1) \end{gathered}$$

$\begin{array}{l}{K}_{{}_4}^{\text{'}}={\mathrm{Î\pm }}_{Z{n}^{2+}}×{\mathrm{Î\pm }}_{y^{4-}}×K_f\\ =1.8×{10}^{-5}×0.3×{10}^{16.5}\\ =1.7×{10}^{11}\end{array}$

Equivalence point=50 mL

Before the equivalence point

The concentration of the remaining productcan be calculated using the following equation

=Fraction remaining × Initial concentration × Dilution factor

If 30 mL solution is added then the reaction will be 30/50 completed as the equivalence point is at 50 mL. Then the metal concentration will be