Calcium ion present in 250-mL of tap water is precipitated with the addition of
ID: 1060097 • Letter: C
Question
Calcium ion present in 250-mL of tap water is precipitated with the addition of sodium oxalate to torn calcium oxalate, CaC_2O_4. An excess of precipitating agent is added to 250-mL of water. The resulting precipitate is filtered, washed, and heated in a crucible to form the more stable calcium oxide, CaO. The mass of the empty crucible was 25.6005 g. The mass of the crucible with the calcium oxide precipitate was 25.7627 g. a) Calculate the grams of Ca^2+ in the water sample. b) Calculate the % Ca^2+ in the water sample. c) Calculate the ppm Ca^2+ in the water sample.Explanation / Answer
a)
V = 250 mL
Ca+2 + C2O4-2 --> CaC2O4
CaC2O4 ---> CaO
mass of preicpitate = 25.7627-25.6005 = 0.1622
this is the mas sof CaO:
MW of CaO = 56.0774
mol = 0.1622/56.0774 = 0.002892 mol of CaO
mol of Ca+2: --> 0.002892 mol
mass of Ca+2 = mol*MW = 0.002892*40 = 0.11568 g = 115.6 mg of Ca+2
b)
% Ca+2 = (total mass of Ca+2 ) /Total mass * 100% = (0.11568 )/(250+0.11568 ) *100= 0.046250%
c)
ppm = mg of Ca+2 /( volume) = 115.6 /250 = 0.4624ppm