1.

Thevapourpressureof waterat 20^(@)C is 17 mm Hg Calculatethe vapourpressureof asolutioncontaining2.8 g of urea (NH_(2)CONH_(2)) in50 g of water .

Answer»


Solution :Vapourpressureof a solvent (water) `=P_(o) =17 mm Hg`
MASS of solvent`= W_(1)= 50 g`
mass ofurea =`W_(2)= 2.8 g`
Molarmass ofwater `= M_(1) =18` g mol
Molar mass of urea `(H_(2)NCONH_(2)) 60 g mol^(-1)`
Vapourpressureof asolution=P= ?
ByRaoult 'slaw
`(P_(o) - P)/(P_(o)) = ( W_(2)xx M_(1))/(W_(1) xx M_(2)) `
`(17- P)/(17) = (2.8 xx 18)/(50 xx 60)= 0.0168`
`:. 17- P =0.0168 xx 17 =0. 2856`
`:. P = 17 - 0.2856 = 16.714 mm Hg`


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