Gravimetry : A sample of elk bone is dissolved in hydrochloric acid, giving 50.0

Question

Gravimetry: A sample of elk bone is dissolved in hydrochloric acid, giving 50.0 mL of solution containing calcium as Ca2+ ion. To precipitate the calcium ion from the resulting solution an excess of potassium oxalate was added. The precipitate of calcium oxalate CaC2O4 weighed 1.437 g.

            (a) What is the mass of calcium in the original bone sample?

            (b) What was the molarity of Ca2+ in the solution?

            (c) What is the concentration of Ca2+ in the solution, expressed in ppm?

Explanation / Answer

V = 50 ml

M = Ca+2

MW CaC2O4= 128.097

m = 1.437 g

mol = mass/MW = 1.437/128.097 = 0.0112 mol of CaC2O4

then

mol of Ca+2 = 0.0112

mass = mol*MW = 0.0112*40 = 0.448 g of C

b)

Molarity

M = mol/V = 0.0112/(50/1000 ) =0.224 M of Ca+2

c)

Ca+2 in ppm

ppm = mg/L

mg = 0.448*1000 = 448 mg

then

ppm of Ca = 448

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