Question

100 ml of a water sample contains 40 mg of
Ca2+ ions. What is the hardness of the water​

Answer 1

Answer:

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Explanation:

Hardness of water in ppm = (mass of CaCO3 / mass of water) x 106 if hardness is caused due to Ca2+

Given mass of Ca2+ ions = 40 mg = 40 x 10–3 g

Number of moles of Ca2+ ions = 40 x 10–3 g / 40 g mol–1 = 10–3 mol

Molar mass of CaCO3 = 100 g mol–1

\therefore mass of 10–3 mol CaCO3 = 10–3 mol . 100 g mol–1 = 10–1 g

Density of water is 1 g/ml.

Thus, mass of 100 ml water is 100 g.

\therefore hardness of water in ppm = (10–1 / 100) x 106 = 103.