91Ó°ÊÓ

Amount of EDTA required for titration = 50 mL of 0.04 M EDTA

Concentration of Cu(NO₃)₂ required for titration =0.08 M

pH maintained =5

EDTA is one type of chelating agent also known as Ethylenediaminetetraacetic acid. It is used to treat heavy metal toxicity, neurotoxicity, lead poisoning, coronary artery disease etc. EDTA has applications in different industries like textile, pulp and paper etc. It is used in biochemistry and molecular biology lab.

Total concentration of EDTA

$\begin{array}{rcl}{K_f}^{\text{'}}& =& \frac{\left[Cu{Y}^{2-}\right]}{\left[C{u}^{2+}\right]\left[EDTA\right]}\\ & =& {\mathrm{Î\pm }}_{Y^{4-}}{K}_f\\ & =& \left(2.9×{10}^{-7}\right)\left({10}^{18.78}\right)\\ & =& 1.74×{10}^{12}\end{array}$

At 0.1 mL Cu (NO₃)₂

Concentration of EDTA

$$\begin{gathered} =\frac{\left(25.0mL-0.1mL\right)}{25.0mL}\left(0.04M\right)\left(\frac{50.0mL}{50.1mL}\right) \\ =0.04M \end{gathered}$$

Concentration of CuY^2-

$$\begin{gathered} =\left(\frac{0.1mL}{50.1mL}\right)\left(0.08M\right) \\ =1.6×{10}^{-4}M \end{gathered}$$

Concentration of Cu²⁺

$\begin{array}{rcl}C{u}^{2+}& =& \frac{\left[Cu{Y}^{2-}\right]}{{K_f}^{\text{'}}\left[EDTA\right]}\\ & =& \frac{1.6×{10}^{-4}M}{\left(1.74×{10}^{12}\right)\left(0.04M\right)}\\ & =& 2.3×{10}^{-15}M\\ pC{u}^{2+}& =& -\log \left(C{u}^{2+}\right)\\ & =& -\log \left(2.3×{10}^{-15}M\right)\\ & =& 14.64\end{array}$

At 25.0 mL Cu (NO₃)₂

Concentration of CuY^2-

$$\begin{gathered} =\left(\frac{25}{75}\right)0.08M \\ =0.027M \end{gathered}$$

Therefore, we can write

$\begin{array}{rcl}\frac{0.027-x}{x^2}& =& 1.74×{10}^{12}\\ x& =& 1.24×{10}^{-7}M\end{array}$

Concentration of Cu²⁺ = 1.24×10^-7 M

$\begin{array}{rcl}pC{u}^{2+}& =& -\log \left(C{u}^{2+}\right)\\ & =& -\log \left(1.24×{10}^{-7}M\right)\\ & =& 6.91\end{array}$

The value of pCu²⁺ for other volumes were calculated following the above calculations.

The values obtained are tabulated below

Graph of pCu²⁺ versus volume of titrant is plotted below