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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 milliequivalents of `Na_(2)CO_(3)` would be required to soften 1 litre of sample ?

Text Solution

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`underset(40g)(Ca^(2+))+underset(2xx23+12xx3xx16=106g)(Na_(2)CO_(3))rarrCaCO_(3)+2Na^(+)`
`"40 g "Ca^(2+)" ions react with "Na_(2)CO_(3)=106g`
`therefore" 20 mg, i.e., "20xx10^(-3)gCa^(2+)` ions will react with `Na_(2)CO_(3)=(106)/(40)xx20xx10^(-3)g=5.3xx10^(-2)g`
`"Equivalent wt. of "Na_(2)CO_(3)=("Mol. wt.")/(2)=(2xx23+12+3xx16)/(2)=53`
`therefore" "5.3xx10^(-2)g Na_(2)CO_(3)=(5.3xx10^(-2))/(53)"g eq."=10^(-3)"g eq. = 1 millieq."`
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