Question
Chemistry Question on Types of Solutions
The hardness of water sample containing 0.002 mole of magnesium sulphate dissolved in a litre of water is expressed as
A
20ppm
B
200ppm
C
2000ppm
D
120ppm
Answer
200ppm
Explanation
Solution
The hardness of water sample containing. 0.002 mole of MgSO4 dissolved in 1 L of water. Number of moles =molecular massmass 0.02=120mass mass=240×10−3g ie, 240×10−3g mass of MgSO4 in 1 L of water. ∴ 103 g of H2O contains = 0.240 g of MgSO4 ∵ 106g of H2O contains =1030.240×106g of MgSO4 =0.240×103g of MgSO4 ∵ 106 g of water contains = 240 g of MgSO4 120 g MgSO4≡100g of CaCO3 240 g of MgSO4 =120100×240=200g of CaCO3 Hence, hardness of H2O=200 ppm