A sample of well water contains 140 gm/m3 Ca2+ ions and 345 gm/m3 Na+ ions. The hardness of the sample of water, expressed in terms of equivalent CaCO3 in gm/m3 is (assuming atomic masses of Ca :40, Na : 23, C : 12, O : 16) ?
Correct answer: A. 350
- A. 350
- B. 485
- C. 140
- D. 345
Explanation
Hardness is due mainly to multivalent ions such as Ca²⁺, while Na⁺ does not contribute appreciably to hardness. Converting calcium to CaCO₃ equivalents gives 140 × (50/20) = 350 g/m³.
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