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A sample of hard water contains 122 ppm ...

A sample of hard water contains 122 ppm of `HCO_3^(ɵ)` ions. What is the minimum weight of CaO required to remove ions completely from 1 kg of such water sample?
(a). 56 mg
(b). 112 mg
(c). 168 mg
(d). 224 mg

A

`56 mg`

B

`112 mg`

C

`168 mg`

D

`244 mg`

Text Solution

Verified by Experts

The correct Answer is:
A
(a) `[MW(HCO_(3)^(ɵ))=62 g,MW(CaO)=56g]`
Temprory hardness is due to the `HCO_(3)^(ɵ)` of `Ca^(2+)` and `Mg^(2+)` and is removed by either boiling or by treating with `CaO` of `Ca(OH)_(2)`(Clark's method).
`underset(" 1 mmol")(Ca(HCO_(3))_(2))+underset("1 mmol")(CaO)tounderset("2 mmol")(2CaCO_(3))+H_(2)O....(1)`
122 p pm of `HCO_(3)^(ɵ)-=122g HCO_(3)^(ɵ)` in `10^(6) mL` or `10^(3)L`
`-=122 mgHCO_(3)^(ɵ)` in `1.0L`
`-=122/61=2 mmol` in `1.0 L`
According to Eq. (i).
2 mmol of `Ca(HCO_(3))_(2)-=2` mmol of `CaO` in `1.0 L`
`=1xx56=56` mg of `CaO`
`=56mg` of `CaO` in `1 kg` of `H_(2)O`
(`1L` of `H_(2)O=1 kg of H_(2)O, :' d H_(2)O=1)`
Hence, the correct option is (a).
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