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

Question

A 100-mL sample of hard water is titrated with the EDTA solution in Problem 2. The same amount of Mg^2+ is added as previously, and the volume of EDTA required is 22.44 mL hat volume of EDTA is used in titrating the Ca^2+ in the hard water? _mL How many moles of EDTA are there in that volume? _moles How many moles of Ca^2+ are there in the 100 mL of water? _moles If the Cu^2+ comes from CaCO_3, how many moles of CaCO_3 are there in one liter of the water? How many grams CaCO_3 per liter? _ moles_g If 1 ppm CaCO_3 = 1 mg per liter, what is the water hardness in ppm CaCO_3? _ppm CaCO_3

Explanation / Answer

Ans.

3.

a) volume of EDTA is used in titrating the Ca 2+ in the hard water

    = 31.83-2.21 = 29.62 ml

b) moles of EDTA = M*Vin L = 0.0193*0.02962 = 0.00057 mole

c) moles of EDTA = moles of Ca 2+ are there in the 100 mL of water

   = 0.00057 mole

d) 1 mole Ca2+ = 1 mole CaCo3

= 0.00057 mole CaCo3 present in 100ml water.

e) mass of CaCO3 = 0.00057*100.1 = 0.057 grams = 57.057 mg

concentration of caco3 = mass in mg /V in L

         = 57.057/0.1 = 570.57 mg/L

water hardness in ppm CaCO3 = 570.57 ppm.

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