Question

The vapour pressure of pure water is 40 mm. If a nonvolatile solute is added to it, vapour pressure falls vapour by 4 mm. Hence, molality of solution is:

1)5.55 m 2)3.0864 m 3)1.543 m 4)0.722 m

Answer 1

Relative lowering in vapour pressure

(Po – P)/Po  = 4/40 = 0.1 = xs

So xo = 0.9

m = 1000*xs/xo*Mo  =  1000*0.1/0.9*18 = 6.17 m

Answer 2

hey mate!

the molality of solution = 6.17