A 100 mL water sample contains 0.81 g of calcium bicarbonate (molar mass 162 g/mol) and 0.73 g of magnesium bicarbonate (molar mass 146 g/mol). Express the total hardness of this water in terms of equivalent CaCO3 content in ppm (mg per litre).

Question

Accepted Answer

10,000 ppm. Hardness is expressed as mg of CaCO3 equivalent per litre (ppm). Ca(HCO3)2: moles = 0.81/162 = 0.005 mol. Each mole gives 1 mol CaCO3 equivalent = 100 g. So 0.005 mol → 0.5 g CaCO3 in 100 mL. Per litre = 5 g = 5000 mg = 5000 ppm. Mg(HCO3)2: moles = 0.73/146 = 0.005 mol. Similarly → 5000 ppm. Total hardness = 5000 + 5000 = 10,000 ppm.

A 100 mL water sample contains 0.81 g of calcium bicarbonate (molar mass 162 g/mol) and 0.73 g of magnesium bicarbonate (molar mass 146 g/mol). Express the total hardness of this water in terms of equivalent CaCO3 content in ppm (mg per litre).

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