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In the determination of hardness of a sa...

In the determination of hardness of a sample of water, the following results were obtained:
Volume of sample `H_(2)O=100 mL` volume of `N//50 Na_(2)CO_(3)` added to it `=20 mL`
volume of `N//50 H_(2)SO_(4)` used to back titrate the unreacted `NA_(2)CO_(3)=10 mL`
Calculate the hardness of water in `gL^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
`0.1 g^(-1)L`
`mEq` of unreacted `Na_(2)CO_(3)=mEq of H_(2)SO_(4)`
`=(1xx10)/50=1/5`
Total `mEq of Na_(2)CO_(3)` taken `=(1xx20)/50=2/5`
`mEq of Na_(2)CO_(3)` absorbed by `H_(2)O=2/5-1/5=1/5`
Weight of `Na_(2)CO_(3)` absorbed by `H_(2)O`
`=1/5xx10^(-3)xx53 g (EW_(Na_(2)CO_(3))=53)`
`=0.0106 g Na_(2)CO_(3)` in `100 mL` of `H_(2)O`
`=(100xx0.0106)/106 g of CaCO_(3)`
`=(0.01xx1000)/100 g of CaCO_(3)` in `1 L of H_(2)O`
`=0.1 g of CaCO_(3)` in `1L of H_(2)O`
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