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A water sample is found to contain 96 pp...

A water sample is found to contain 96 ppm of `SO_4^(2-)` and 122 ppm of `HCO+3^(ɵ)` with `Ca^(2_)` ion as the only cation.
(a). Calculate the ppm of `Ca^(2+)` in water.

Text Solution

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In 1000 kg of water the mass of `HCO_(3)^(-) = 183 g`
Moles of `HCO_(3)^(-) = (183)/61 = 3`
Moles of `SO_(4)^(2-) = 96/96 = 1`
` :. ` Total moles of `Ca^(2+)` in the solution ` = 1 + 1.5 = 2.5`
`Ca(HCO_(3))_(2) + CaO to 2CaCO_(3) + H_(2)O`
Moles of CaO required to be added to remove all `HCO_(3)^(-) = 1.5`
Now, the `Ca^(2+)` in the solution will be only associated with `SO_(4)^(2-)`. Therefore , moles of `Ca^(+2)` left in the solution = 1 .
ppm of `Ca^(2+) = 1 xx 40 = 40` ppm
Moles of `Ca^(2+) ` ions in 1 L of `H_(2)O = 10^(-3)`
Moles of `H^(+)` ions that `Ca^(2+)` will exchange with `= 2 xx 10^(-3)`
` :. pH = - log (2 xx 10^(k^(3))) = 2.7`
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