Question

a) Calculate the moles of EDTA if 32.1 mL of 0.0217M EDTA is required to reach the endpoint in the titration of 25.00mL of a water sample.

b) Calculate the moles of Ca2+ in the water sample.

c) Calculate the ppm of CaCO3 in the water sample.

Answer 1

a) moles of EDTA = molarity x volume

                               = 0.0217 x 32.1 / 1000

                              = 6.94 x 10^-4

moles of EDTA = 6.94 x 10^-4

b)

EDTA + Ca+2 ---------------> Ca-EDTA

moles of EDTA = mole of Ca+2

moles of Ca+ 2 in water = 6.94 x 10^-4

c)

moles of Ca+2 = moles of CaCO3 = 6.94 x 10^-4

volume = 25 mL

molarity of CaCO3 = moles / volume

                             = 6.94 x 10^-4 / 0.025

                           = 0.0279 mol / L

                         = 0.0277 mol / L x 100 g / mol

                         = 2.776 g / L

                          = 2776 mg / L

                          = 2776 ppm