1.

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_4undergoes complete ionisation.

Answer»

Solution :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 (1000g kg^(-1))/(50G)`
` Delta T_f = 1.57`
` T_f = -1.57^@C " or " 271.43 K`


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