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(a) State Raoult's law for a solution co...

(a) State Raoult's law for a solution containing volatile components.
How does Raoult' s law become a special case of Henry's law?
(b) 1.00 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. Find the molar mass of the solute. `(K_(f)" for benzene "=5.12 kg mol^(-1))`

Text Solution

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(a) Raoult' s Law states that for a solution of volatile liquids the partial vapour pressure of each component is directly proportional to it mole fraction. The relative lowering of vapour·pressure is equal to mole fraction of solute in case of non- volatile s·olute. Because, Henry's Law also states that ~'the partial pressure of the gas in vapour phase (P) is proportional to the mole fraction of the gas (x) in the solution".
(b) Substituting the values of various terms involved in equation, `M_(B)=(K_(F)xxW_(B)xx1000)/(DeltaT_(F)xxW_(A))` we get. `M_(2)=(5.13K" kg "mol^(-1)xx1.00gxx1000g" "kg^(-1))/(0.40xx50g)=256 g" "mol^(-2)`
Thus, molar mass of the solute `=256g mol^(-1)`.
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