Solutions With Positive Deviation

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These types of solutions where DH of mixing is >0 and DV of mixing >0 are found to exhibit positive deviation from Raoult's law. Here solute-solute interactions and solvent-solvent interactions are greater than solute - solvent interactions.

fig.3.7

Consider a solution of liquid mixtures A and B.

As expected from Raoult's law.

An e.g., of such liquid mixture is ethanol n hexane mixture. The H-bond in ethanol molecules are broken by the n hexane molecules coming in between the ethanol molecules. As a result the escaping tendency increases there by increases the vapor pressure of individual component therefore a positive deviation is observed.

Other examples are:

1) (CH₃)₂CO + CS₂Acetone       Carbon-di-sulphide

2) C₆H₆ + (CH₃)₂COBenzene acetone

3) CH₃OH + H₂OMethanol water

4) CCl₄ + C₆H₆

5) CCl₄ + CHCl₃

6) CCl₄ + C₆H₅CH₃

7) H₂O + CH₃OH

8) H₂O + C₂H₅OH