Chapter 26

You are the analyst working in a hospital laboratory. A urine sample from a patient must be analysed for \(\mathrm{Ca}^{2+}\) and \(\mathrm{Mg}^{2+}\) ions by the following procedure. The urine sample was diluted to exactly \(2.000 \mathrm{~L}\). After buffering to \(\mathrm{pH}=10\), a sample \((25.00 \mathrm{~mL})\) required EDTA (24.00 mL; \(0.0500 \mathrm{M}\) ) for equivalence. In a second sample \((50.00 \mathrm{~mL})\), the \(\mathrm{Ca}^{2+}\) was precipitated as calcium oxalate which was filtered, washed and re-dissolved in acid. To this solution EDTA \((25.00 \mathrm{~mL} ; 0.05 \mathrm{M})\) was added and the resulting solution buffered to \(\mathrm{pH}=10\) and titrated to equivalence with an \(\mathrm{MgCl}_{2}\) solution \((10.00 \mathrm{~mL} ;\) \(0.0500 \mathrm{M})\). From these results, calculate the amount of \(\mathrm{Ca}^{2+}\) and \(\mathrm{Mg}^{2+}\) (in mg) in the \(2.000 \mathrm{~L}\) solution.