The vapour pressure of pure water at `20^(@)C` is 17.5 mm of Hg. A solution of sucrose is prepared by dissoving 68.4 g of sucrese in 1000 g of water. Calculate the vapour pressure of the solution.

Answer

(i) `0.0036` (ii) 17.437 mm Hg

Explanation

Mole of sucrose `= (68.4)/(342) = 0.2`
Moles of water ` = (1000)/(18) = 55.56`
Mole fraction of surcose ` = (0.2)/(0.2+55.56) = 0.0036`
(i) Relative lowering of vapour pressure = Mole fraction of solute ` = 0.0036`
(ii) ` (p_(A)^(@) - p_(A))/(p_(A)^(@)) = 0.0036 or (17.5 p_(A))/(17.5) = 0.0036`
` therefore " "p_(A) = 17.437mm Hg`