Calculate the freezing point of solution when 2 g of `Na-2SO_4 (M = 142 g "mol"^(-1))` was dissolved in 50 g of water, assuming `Na_2 SO_4` undergoes complete ionisation.

Explanation

Molality of the solution = ` = (2//142)/(50) xx 1000m`
For complete ionisation of `Na_2SO_4 , i= 3`
Apply the relation
` Delta T_f = iK_f m`
Substituting the values, we have
` Delta T_f = 2 xx 1.86 kg "mol"^(-1) xx (2g)/(142 "mol"^(-1)) xx (1000 g kg^(-1))/(50g)`
` Delta T_f = 1.57`
` T_f = -1.57^@C " or " 271.43 K`