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Explain the positive deviation exhibited by non-ideal solution with prefernce to a solution of ethyl alcohol and water. |
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Answer» Solution :The nature of the deviation from the Rauolt's law can be explained in terms of the intermolecular interactions between solute (A) and solvent (B). CONSIDER a case in which the intermolecular attractive forces between A and B are weaker than those between the molecules of A(A-A) and molecules of B(B-B) .The molecules present in such a solution have a greater tendency to escape from the solution when compared to the ideal solution formed by A and B in which the intermoleculr attractive forces (A-A,B-B.A-B) are almost similar .Consequently the vapour pressure of such non-ideal solution increases and it is greater then the sum of the RAOULT's law This type of deviation is called positive deviation Here , `P_A gt P_A^(@) X_A and P_B gt P_B^(@) X_B ` Hence ` P_("total ")lt P_A^(@) X_A + P_B^(@) X_B ` Let us understand the positive deviation by considering a solution of ethyl alcohol and water . In this solution the hydeogen bonding interaction between ethanol and water is weaker than those hydrogen bonding interactions amongst themselves (ethyl alcohol -ethyl alcohol and water-water interactions ) .This results in the increased evaporation of both COMPONENTS from the aqueous solution of ethanol .Consequently .the vapour pressure of the solution is greater than the vapour pressure predicted by Raoult's law .Here the mixing process is endothermic i.e `Delta H_("mixing " )lt 0 ` and there will be a slight increase in volume `(Delta V_("mixing ")lt 0.) ` Examples for non-ideal solution showing positive DEVIATIONS : Ethyl alcohol & cyclohexane . Benzene & acetone Carbon tetrabhloride& chloroform . Acetone & ethyl alcohol , Ethyl alcohol & water ` (##SUR_CHE_XI_V02_C09_E05_003_S01.png" width="80%"> |
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