Question

The hardness of water sample containing 0.002 mole of magnesium sulphate dissolved in a little of water is expressed as

Answer 1

1 mol MgSO4=1molCaco3MgSO4=1molCaco32 mol MgSO4=2molCaco3MgSO4=2molCaco3i.e 2×100gCaCO32×100gCaCO3∴∴ Hardness of water = 220 ppm

Answer 2

The degree of hardness of water sample is 200 ppm

Explanation:

The hardness of water is the concentration of multivalent cations

In 1 lit of water

moles of MgSO₄ = 0.002

Molecular weight of MgSO₄= 120

Valency = 2

We know that

Equivalent Weight = Molecular Weight/Valency

Thus, Gram equivalents of MgSO₄ = (Weight of MgSO₄ × Valency)/Molecular Weight

or, Gram equivalents of MgSO₄ = 0.002 × 2 = 0.004

Now,

Gram equivalents of MgSO₄ = Gram equivalents of CaCO₃

0.004 = Weight of CaCO₃/Equivalent weight of CaCO₃

or, 0.004 = Weight of CaCO₃/(100/2)

or, 0.004 = Weight of CaCO₃/50

or, Weight of CaCO₃ = 0.004× 50

                                   = 0.2 gram

                                   = 200 mg

Thus, the hardness as of CaCO₃ = 200 mg/lt = 200 ppm

Therefore, the degree of hardness of water sample = 200

Hope this answer is helpful.

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