Question

Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%

Answer 1

Answer:

Let p be the vapour pressure of pure octane. The vapour pressure of solution will be  

100 /80 p  =0.8 p

Molar mass of solute (M) and octane (m)  are 40 g/mol and 114 g/mol respectively. Mass of octane, w is 114 g.

(p-p')/p = W x114 / 40 x 114

W = 8g

Thus, 8g of solute is required