Question

The degree of hardness of sample of water containing 27.2 mg of CaSO4 per Kg of water is

Answer 1

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What is the degree of hardness of a sample of water containing 24 mg of MgSO

4

(mol. mass 120) per kg of water?

Medium

Solution

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Correct option is C)

Given, 1 kg of water contains 24 mg of MgSO

4

.

So 1 kg=1000 g of water.

1 million grams of water =1000×1000 g contains 24 mg×1000=24 g of MgSO

4

1 mole of MgSO

4

=1 mole of CaCO

3

120 g of MgSO

4

=100 g of CaCO

3

24 g of MgSO

4

=(x) g of CaCO

3

So, x=

120

24×100

=20

So, degree of hardness =20 ppm

Answer 2

The degree of hardness of water sample is 147 ppm

Explanation:

The hardness of water is the concentration of multivalent cations

In 1 lit of water

Wt of CaSO₄ = 200 mg = 0.2 gram

Molecular weight of CaSO₄= 136

Valency = 2

We know that

Equivalent Weight = Molecular Weight/Valency

Now,

Gram equivalents of CaSO₄ = Gram equivalents of CaCO₃

Weight of CaSO₄/Equivalent Weight of CaSO₄= Weight of CaCO₃/Equivalent weight of CaCO₃

or, 0.2/(136/2) = Weight of CaCO₃/(100/2)

or, 0.2/68 = Weight of CaCO₃/50

or, Weight of CaCO₃ = (0.2/68) × 50

                                  = 0.147 gram

                                  = 147 mg

Thus, the hardness as of CaCO₃ = 147 mg/lt = 147 ppm

Therefore, the degree of hardness of water sample = 147

Hope this answer is helpful.