Chemistry - Coordination Chemistry Question with Solution | TestHub

The total concentration of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ in a sample of hard water was determined by titrating a $0.1\mathrm{L}$ sample of water with a solution of $[\mathrm{EDTA}{]}^{4-}$. The $[\mathrm{EDTA}{]}^{4-}$ chelates the cations.

${\mathrm{Mg}}^{2+}+[\mathrm{EDTA}{]}^{4-}\to [\mathrm{Mg}\left(\mathrm{EDTA}\right){]}^{2-}$

${\mathrm{Ca}}^{2+}+[\mathrm{EDTA}{]}^{4-}\to [\mathrm{Ca}\left(\mathrm{EDTA}\right){]}^{2-}$

It requires $31.5\mathrm{mL}$ of $0.0104\mathrm{M}[\mathrm{EDTA}{]}^{4-}$ solution to reach the endpoint in the titration. A second $0.1\mathrm{L}$ sample was then treated with sulfate ion to precipitate ${\mathrm{Ca}}^{2+}$ as ${\mathrm{CaSO}}_4$. The ${\mathrm{Mg}}^{2+}$ was then titrated with $18.7\mathrm{mL}$ of $0.0104\mathrm{M}[\mathrm{EDTA}{]}^{4-}$. Calculate the hardness due to calcium.