Question

The relative lowering of the vapour pressure is equal to the ratio between the number

• A. solute molecules to the solvent molecules
• B. solute molecules to the total molecules the solution
• C. solvent molecules to the total molecules B in the solution
• D. solvent molecules to the total number ions of the solute

Answer 1

Answer: (B)

According to Raoulfs law, relative lowering in vapour pressure is directly proportional to the mole fraction of solute, ie, $ \frac{{{P}^{o}}-P}{{{P}^{o}}}{{\chi }_{s}} $ where $ {{\chi }_{s}}=\frac{{{n}_{s}}}{{{n}_{s}}+N}=\frac{moles\,of\,solute}{total\,number\,of\,moles} $ $ \therefore $ relative lowering of vapour pressure $ =\frac{{{n}_{2}}}{{{n}_{1}}+{{n}_{2}}}=\frac{solute\,molecules}{total\,molecules\,in\,the\,solution} $