A 3.50 g rock was analysed to determine the amount to calcium present. The rock was dissolved in excess sulfuric acid, whereby all the calcium present was converted into Ca2+ . The resulting solution of calcium ions was then reacted with an oxalate solution to precipitate the calcium ions forming calcium oxalate. Following this the pure solid calcium oxalate was filtered from the solution, dried in an oven for 24 hours and weighed using the constant mass method. 

The final mass of the calcium oxalate was determined to be 2.15 g.

                                                                                                         

                                                                                                         Ca2+(aq) + C2O4 2- (aq) → CaC2O4(s)

a. What analytical method was utilised in this procedure?
b. Calculate the number of moles of pure calcium oxalate precipitated.
c. Determine the number of moles of Ca2+ present.
d. Calculate the percentage by mass of Ca2+ present in the sample of limestone.