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State Raoult's law for solutions containing non-volatile solutes in volatile solvents. Derive a mathematical expression for the law. |
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Answer» Solution :Raoult.s law. It states that at any TEMPERATURE, PARTIAL vapour PRESSURE of a volatile component of a solution is equal to the vapour pressure of that component and its mole fraction in solutions. Let two volatile liquid components A and B of a solution has mole fractions `X_A and X_B` respectively. Let `P_(A)^(@) =` V.P. of pure A in solution. `P_(B)^@ = V.P.` of pure B in solution. `P_(A)` = Partial V.P. of A in solution. `P_B` = Partial V.P. of B in solution. According to Raoult.s law, `P_A = P_(A)^(@)X_A` `P_B = P_(B )^(@) X_B` Total V.P. of solution, `P = P_A + P_B ` `P = P_(A)^(@) X_A +P_(B)^(@) X_B` If the component B is a non-volatile solute. `P_B = 0` ` therefore P = P_A = P_(A)^(@) X_ A` `or (P_A)/(P_(A)^(@))=X_A` `(P_A)/(P_(A)^(@))=1-X_B` or ` 1-(P_A)/(P_(B) ^(@) )=X_B` `(P_A^(@)-P_A)/(P_(A)^(@))=X_B` |
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