Gradebook O 11/20/2016 11:55 PM A 7.3/10 11/15/2016 10:36 PM Print Calculator Pe

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Gradebook O 11/20/2016 11:55 PM A 7.3/10 11/15/2016 10:36 PM Print Calculator Periodic Table Question 15 of 15 A Map A macmillan learning Sapling Learning Hardness in groundwater is due to the presence of metal ions, primarily Mg2 and Ca2 Hardness is generally reported as ppm CaCO3. To measure water hardness, a sample of groundwater is titrated with EDTA, a chelating agent, in the presence of the indicator eriochrome black T, symbolized here as In Eriochrome black T, a weaker chelating agent than EDTA, is red in the presence of Ca 2+ and turns blue when Ca 2+ s removed blue red Ca (In): EDTA Ca (EDTA) In A 50.00-mL sample of groundwater is titrated with 0.0900 M EDTA. Assume that Ca2 accounts for all of the hardness in the groundwater. If 13.00 mL of EDTA is required to titrate the 50.00-mL sample, what is the hardness of the groundwater in molarity and in parts per million of CaCO3 by mass? Number MI CaCO Number ppm Caco, Previous 3 Give Up & View Solution Check Answer Nex Exit Hint

Explanation / Answer

mmoles EDTA = Molarity EDTA x mL EDTA = (0.0900)(13.00) = 1.17 mmoles EDTA

Because EDTA reacts with Ca2+ in a 1:1 mole ratio, then

mmoles Ca2+ = mmoles EDTA = 1.17

Molarity Ca2+ = mmoles Ca2+ / mL Ca2+ = 1.170 / 50.00 = 0.0234 M Ca2+
x (1 mole CaCO3 / 1 mole Ca2+) = 0.0234 M CaCO3

(0.0234 moles CaCO3 / L) x (100 g CaCO3 / 1 mole CaCO3) x (1000 mg / 1 g) x
= 2340 mg CaCO3 / L = 2340 ppm CaCO3

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