1.

Calcualate the amount of `NaCl` which must be added to `100 g` water so that the freezing point, depressed by `2 K`. For water `K_(f)` =`1.86 K kg mol^(-1)`.

Answer» `NaCl` is a strong electrolyte. It is completely dissociated in solution.
Degree of dissociation, `alpha=1`
`NaClhArrunderset((n=2))(Na^o++Cl^(ө))`
Number of particles after dissociation =`1+(n-1)alpha`
`=1+(2-1)xx1`
`=2`
`DetlaT_(obs)/DetlaT_(theo)="Number of particles after dissociation"/"Number of particles when there is no dissociation"`
`2/DetlaT_(theo)=2`
ot `DetlaT_(theo)=1`
Let W g of NaCl be dissolved in `100 g` of water.
So `DetlaT_(theo)=(1000xxK_(f)xxW_(2))/(W_(1)xxMw_(1))`
or`W_(2)=(DetlaT_(theo)xxW_(1)xxMw_(1))/(1000xxK_(f))`
`(1xx100xx58.5)/(1000xx1.86) = 3.145 g`


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