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A sample of hard water contains 20 mg of...

A sample of hard water contains 20 mg of `Ca^(2+)` ions per litre. How many millimoles of `Na_(2)CO_(3)` would be requried to soften 1 L of the sample. Also calculate the mass of `Na_(2)CO_(3)`.

Text Solution

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Reaction: `Ca^(2+)+Na_(2)CO_(3) toCaCO_(3)+2Na^(+)`
Number of moles of `Na_(2)CO` molecules
=Number of moles of `Ca^(2+)` ions`=(20xx10^(-3))/(40)=5xx10^(-4)`
`therefore`Number of millimoles of `Na_(2)CO_(3)` required to soften 1L of the sample`=5xx10^(-4)xx10^(3)=0.5`
`therefore`Mass of `Na_(2)CO_(3)=5xx10^(-4)xx106=0.05g`.
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