Question

Considering a binary solution of components A and B obeys Raoult’s law, which of the following is true?

(a) Total vapor pressure cannot be related to mole fraction of only one component

(b) Total vapor pressure of one component varies non-linearly with another component

(c) A plot of vapor pressures of both components gives a linear plot

(d) Total vapor pressure of solution always decreases with increase in mole fraction of a component

I got this question in examination.

My query is from Vapour Pressure of Liquid Solutions topic in section Solutions of Chemistry – Class 12

Answer 1

Correct choice is (c) A plot of vapor pressures of both components gives a linear plot

The best I can explain: Raoult’s law states that the partial pressure of each component in the solution varies directly with its mole fraction in the solution. It is formulated as ptotal = pA + (pB – pA)xB. From this, it is seen that when a graph is plotted, it gives a linear plot passing through origin. Total vapor pressure can be expressed as mole fraction of one component and that it varies linearly with the latter. However, total vapor solution may decrease or increase with increase in mole fraction of a component.