Question

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

• A. $20\, ppm$
• B. $200\, ppm$
• C. $2000\, ppm$
• D. $120\, ppm$

Answer 1

The Correct Option is B

The hardness of water sample containing. 0.002 mole of $ MgS{{O}_{4}} $ dissolved in 1 L of water. Number of moles $ =\frac{mass}{molecular\text{ }mass} $ $ 0.02=\frac{mass}{120} $ $ mass=240\times {{10}^{-3}}g $ ie, $ 240\times {{10}^{-3}}g $ mass of $ MgS{{O}_{4}} $ in 1 L of water. $ \therefore $ $ {{10}^{3}} $ g of $ {{H}_{2}}O $ contains = 0.240 g of $ MgS{{O}_{4}} $ $ \because $ $ {{10}^{6}}g $ of $ {{H}_{2}}O $ contains $ =\frac{0.240\times {{10}^{6}}}{{{10}^{3}}}g $ of $ MgS{{O}_{4}} $ $ =0.240\times {{10}^{3}}g $ of $ MgS{{O}_{4}} $ $ \because $ $ {{10}^{6}} $ g of water contains = 240 g of $ MgS{{O}_{4}} $ 120 g $ MgS{{O}_{4}}\equiv 100g $ of $ CaC{{O}_{3}} $ 240 g of $ MgS{{O}_{4}} $ $ =\frac{100\times 240}{120}=200g $ of $ CaC{{O}_{3}} $ Hence, hardness of $ {{H}_{2}}O=200 $ ppm