Question

The vapour pressure of water at 37° C is 150 mm Hg. An aqueous solution containing
28% by mass of a liquid B (M = 140 g/mol) has a vapour pressure of 160 mm Hg,
calculate
(i) vapour pressure of pure liquid B;
(ii) composition of two components in the vapour phase;
(iii) vapour pressure of a solution containing equal mass of the two liquids;
(iv) vapour pressure of a solution containing equal number of moles of the two liquids.

Answer 1

Explanation:

for total miscible liquids,ptotal=mol.fraction of a*pa0+ mol. fraction of b* pB0 no. of moles of a= 28/140 liquid b in water.its mass is (100-28),i.e.,72.no.of moles of b=72/18 to talk number of moles=0.2+4.0=4.2 given, ptotal=160mm pb0=150mm so 160= 0.2/4. 2*pb0+4.0/4.2*150 pa0=17.15*4.2/0.2=360.15 mm.