Question

The relative lowering of vapour pressure of an aqueous solution containing a non-volatile solute, is 0.0125. The molality of the solution is
A. `0.70`
B. `0.50`
C. `0.90`
D. `0.80`

Answer 1

Correct Answer - A
`(p^(@)-p_(s))/(p^(@))=x_(2)rArr(p^(@)-p_(s))/(p^(@))=(wN)/(mW)`
`0.0125=(wM)/(mW)rArr(w)/(mW)=(0.0125)/(18)=0.00069`
`"Hence, molality"=(w)/(mW)xx1000=0.00069xx1000=0.69`
`~=0.70`