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The vapour pressure of water at 20^(...

The vapour pressure of water at `20^(@)C` is 17 mm Hg Calculate the vapour pressure of a solution containing 2.8 g of urea `(NH_(2)CONH_(2))` in 50 g of water .

Text Solution

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The correct Answer is:
Vapour pressure of the solution =16.714 mm Hg
Vapour pressure of a solvent (water) `=P_(o) =17 mm Hg`
Mass of solvent `= W_(1) = 50 g`
mass of urea = `W_(2) = 2.8 g`
Molar mass of water `= M_(1) =18` g mol
Molar mass of urea `(H_(2)NCONH_(2)) 60 g mol^(-1)`
Vapour pressure of a solution =P= ?
By Raoult 's law
`(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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