Sapling Learning Hardness in groundwater is due to the presence of metal ions, p

Question

Sapling Learning Hardness in groundwater is due to the presence of metal ions, primarily Mg and Ca". Hardness is generally reported as ppm CaCOs 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 Ca2 and tuns blue when Ca* is removed. red blue Calld'+-EDTA-> Ca(EDTA)"++In A 50.00-mL sample of groundwater is titrated with 0.0200 M EDTA Assume that Ca accounts for all of the hardness in the groundwater. If 11.00 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 CaCOs by mass? M Caco, ppm CacO, Previous Group & View

Explanation / Answer

Solution:- From given equation, Ca2+ reacts with EDTA in 1:1 mol ratio.

We would use the molarity equtaion, M1V1 = M2V2 to calculate the concentration of Ca2+ in the water sample.

0.0200 M x 11.00 mL = M2 x 50.00 mL

M2 = 0.0200 M x 11.00 mL/50.00 mL

M2 = 0.0044 M

So, the molarity of CaCO3 in hard water sample is 0.0044 M.

ppm is mg of solute per liter of solution. So, let's convert mol/L to g/L and then mg/L.

Molar mass of CaCO3 is 100. g/mol.

(0.0044 mol/L) x (100 g/mol) x (1000 mg/g) = 440 mg/L or 440 ppm

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