Question

Washing soda (`Na_2CO_3.10H_2O`) is widely used in softening of hard water. If `1L` of hard water requires 0.0143g of washing soda, what is hardness of water in terms of `p p m` of `CaCO_3`?

Answer 1

Correct Answer - 5
`MW` of washing soda=`286`, MW of `CaCO_(3)=100 gmol^(-1)`
`CaSO_(4)+Na_(2)CO_(3)toCaCO_(3)+Na_(2)SO_(4)`
`0.0143` g of `N_(2)CO_(3)=.10 H_(2)O=(0.0143xx10^(3))/(286//2)`
`=0.1 mEq`
`0.1` mEq of `Na_(2)CO_(3)=0.1/2` mmol of `CaCO_(3)` in `1L`
=`(0.05xx10^(-3))xx100g` in `10^(3) mL`
`=0.005 g ` in `10^(3)mL=5` p p m of `CaCO_(3)`