4. The total concentration of $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ in a sample of a hard water was determined by titrating a $0.100 \mathrm{~L}$ sample of the water with a solution of EDTA $^{4}$. It requires $31.50 \mathrm{~mL}$ of $0.0104 \mathrm{M}$ solution to reach the end point in the titration. A second $0.100 \mathrm{~L}$ sample was then treated with sulfate ion to precipitate $\mathrm{Ca}^{2+}$ as calcium sulfate. The $\mathrm{Mg}^{2+}$ was then titrated with $18.70 \mathrm{~mL}$ of $0.0104 \mathrm{M}$ EDTAt. a. Write the complexation reaction between calcium ions, magnesium ions and EDTA. b. Calculate the concentrations of $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ in the hard water in $\mathrm{mg} \mathrm{L}^{-1}$.

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