3. A 100 mL sample of hard water is titrated with the EDTA solution in Problem 2

Question

3. A 100 mL sample of hard water is titrated with the EDTA solution in Problem 2. The same amount of the Mg^2+ is added as previously , and the volume of EDTA required is 31.84mL.

a. What volume of EDTA is used in titrating the Ca^2+ in the Hard water?

b. How many moles of EDTA are there in that volume?

c. How many moles Ca^2+ are there in the 100 mL of water?

d. If the Ca^2+ comes from CaCO3 , how many moles of CaCO3 are there in one liter of the water? How many grams CaCO3 per liter?

e. If 1 ppm CaCO3 = 1mg liter, what is the water hardness in ppm CaCO3?

Explanation / Answer

a) Volume EDTA used in titrating Ca2+ in hard water is 15.04 m

b) 5.12x10-4 mol EDTA in 27.56 mL

c) 20.48x10-4 mol Ca^2+ in 25.00 mL solution

d) 0.005113 mol CaCO3 in 1 lt of the water

e) water is 176ppm CaCO3 hardness as CaCO3

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