Non ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example of each type.

Non ideal solutions exhibit either positive or negative deviations fro

1.	Non ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example of each type.
Answer» The cause for these deviations lies in the nature of interactions at the molecular level. In case of positive deviation from Raoult‘s law, A-B interactions are weaker than those between A-A or B-B, i.e., in this case the intermolecular attractive forces between the solute-solvent molecules are weaker than those between the solute-solute and solvent-solvent molecules. This means that in such solutions, molecules of A (or B) will find it easier to escape than in pure state. This will increase the vapour pressure and result in positive deviation. Mixtures of ethanol and acetone behave in this manner. In case of negative deviations from Raoult‘s law, the intermolecularattractive forces between A-A and B-B are weaker than those between A-B and lead to decrease in vapour pressure resulting in negative deviations. An example of this type is a mixture of phenol and aniline.

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Non ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example of each type.

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