The degree of dissociation of `Ca(NO_(3))_(2)` in a dilute aqueous solution, containing `7.0 g` of the salt per `100 g` of water at `100^(@)C` is `70%`. If the vapour pressure of water at `100^(@)C` is `760 mm`, calculate the vapour pressure of the solution.

Explanation

`{:(1,,,,,,,,),(Ca(NO_(3))_(2),,to,,Ca^(2+),,+,,2NO_(3)^(-)),(1-x,,,,x,,,,2x):}`
van.t Hoff factor `i=(1-x+x+2x)/(1)=(1+2x)/(1)=1+2xx0.7=2.4`
Now, `i=("observed lowering of vapour pressure")/("normal lowering of vapour pressure")`
`:.` obs. lowering of vap. press. `=ixx` nor.lowering of vap.press.
`p^(0)-p_(obs.)=ixx{(n)/(n+N).p^(0)}`
`760-p_(obs)=2.4xx(7//164)/((7)/(164)+(100)/(18))xx760` `{{:(Ca(NO_(3))_(2)=164),(H_(2)O=18):}}`
`=13.90`
`:.p_(obs.)=760-13.90=746.10mm`