Onelitre sample of water contains 0.9mg of NaCl2 and 0.9mg of MgCl2. Find the total hardness in terms of parts permillion of CaCO3.
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Solution
111gCaCl2≡100gCaCO3 ∴0.9mgCaCl2≡100111×0.9mgCaCO3 ≡0.81mg of CaCO3 95gMgCl2≡100gCaCO3 ∴0.9mgMgCl2≡10095×0.9mgCaCO3 ≡0.94mg of CaCO3 Thus, 1 litre waterr of 106 mg water contains (0,81+0.94=1.75mg) i.e., hardness of water is 1.75ppm.