The amount of solute (molar mass 60 g `mol^(-1)`) that must be added to 180 g of water so that the vapour pressure of water is lowered by `10%` is

Options

A. 30 g
B. 60 g
C. 120 g
D. 12 g

Answer

B

Explanation

If `p^(@)="100 mm, "p_(s)=100-10="90 mm"`
`(p^(@)-p_(s))/(p^(@))=(w_(2)//M_(2))/(w_(1)//M_(1))=(w_(2))/(M_(2))xx(M_(1))/(w_(1))`
`(100-90)/(100)=(w_(2))/(60)xx(18)/(180)`
`"or "w_(2)=(10)/(100)xx60xx10=60g.`