Question

Which of the following is the expression of Raoults law? ( $ p= $ vapour pressure of pure solvent, $ {{p}_{s}}= $ vapour pressure of the solution)

• A. $ \frac{p-{{p}_{s}}}{p}=\frac{n}{n+N} $
• B. $ \frac{{{p}_{s}}-p}{p}=\frac{N}{N+n} $
• C. $ \frac{p-{{p}_{s}}}{{{p}_{s}}}=\frac{N}{N-n} $
• D. $ \frac{{{p}_{s}}-p}{{{p}_{s}}}=\frac{N-n}{N} $

Answer 1

Answer: (A)

According to Raoults law, for non-volatile solute, the relative lowering of vapour pressure of a solution is equal to the mole fraction of the solute. $ \frac{p-{{p}_{s}}}{p}=\frac{n}{n+N} $