Calculate the vapour pressure lowering caused by addition of `50g` of sucrose (molecular mass `= 342)` to `500g` of water if the vapour pressure of pure water at `25^(@)C` is `23.8 mm Hg`.

Explanation

According to Raoult's law,
`(p_(0)-p_(s))/(p_(0))=(n)/(n+N)`
or`Deltap=(n)/(n+N).p_(0)`
Given:`n=(50)/(342)=0.146,N=(500)/(18)=27.87and p_(0)=23.8`
Substituting the values in the above equation,
`Deltap=(0.146)/(0.146+27.78)xx23.8=0.124` mm Hg.