Question

Name Section Experiment 28 Advance Study Assignment: Determination of the Hardness of Water 1. A 0.3946 g sample of Caco, is dissolved in 12 M HCl and the resulting solution is diluted to 250.0 mL in a volumetric flask. a. How many moles of Caco, are used (formula mass = 100.1)? moles b. What is the molarity of the Ca2+ in the 250 mL of solution? c. How many moles of Caare in a 25.00-mL aliquot of the solution in 1b? moles 2. 25.00-mL aliquots of the solution from Problem 1 are titrated with EDTA to the Eriochrome Black T end point. A blank containing a small measured amount of Mg + requires 2.77 mL of the EDTA to reach the end point. An aliquot to which the same amount of Mg?* is added requires 39.04 mL of the EDTA to reach the end point. ion in the aliquot? a. How many milliliters of EDTA are needed to titrate the Ca b. How many moles of EDTA are there in the volume obtained in Parta? moles c. What is the molarity of the EDTA solution? (continued on following page)

Answer 1

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Weight of CaCO₃ formula mass of sample CaCO3 = = 0.3946 g. 100.1 g/mol h : moles of CaCO3 = . gram Formula mass 0.3946 . 100.1 = 3.942 x 10-3 mol 16 Molarity - moles of Ano Volume of solute solution (L) 3.942 x 10-3 250 1000 • 10 = 0.0158M Imol Caco, produce 1 mol Ca 2+ ion . [G 2+] = 0.0158 MI Moles of Ca 2+ = Molarity & Volume linL). 0.0158 x 25 1000 = 3.94 x 10-4 mol.