Question

The density of 2M solution of a solute is 1. 2g/ml. If the molecular weight of the solute is 100g/mol then the molality of tge solution is

a)2 b)1. 2 c)1 d)0. 6 e)2. 4

Answer 1

There is a straight formula for converting w/w% into molarity.

Molarity={(w/w%)×10×(density in g/ml)}÷(Molar mass of solute in g)

Putting values, M=(98×10×1.8)/(98)=18M

Now, Normality=Molarity×n-factor

Putting values, N=18×2=36N (n-factor is 2 because H2SO4 is a dibasic acid)

Molality is a bit tricky because the formula involves tedious calculation.

Molality=(1000×Molarity)/{(1000×density in g/ml)-(Molar mass of solute in g×Molarity)}

Putting values,

m=(1000×18)/{(1000×1.8)-(98×18)}

=18000/(1800–1764)

=18000/36=500m