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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.

 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. 

Grade:12

4 Answers

Himalaya Pramanick
63 Points
8 years ago
The deviations are caused due the difference in attractive forces between the molecules.Let us consider we are mixing 2 chemicals – A & B,let the attraction between A-A molecules in pure A solution & B-B molecules in pure B solution is less then the attraction between A-B in the mixture.This causes decrease in volume and ‘-‘ve deviation. ‘+’ve deviantion is caused if A-B attractive force is weak. The difference in attractive force is due to various factors like Hydrogen bonding,dipole-dipole attraction etc..
 
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Nicho priyatham
625 Points
8 years ago
 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
EX  Mixtures of ethanol and acetone behave in this manner. In pure ethanol, molecules are hydrogen bonded. On adding acetone, its molecules get in between the host molecules and break some of the hydrogen bonds between them. Due to weakening of interactions, the solution shows positive deviation from Raoult’s law
 negative deviations from Raoult’s law, the intermolecular attractive forces between A-A and B-B are weaker than those between A-B and leads to decrease in vapour pressure resulting in negative deviations. An example of this type is a mixture of phenol and aniline. In this case the intermolecular hydrogen bonding between phenolic proton and lone pair on nitrogen atom of aniline is stronger than the respective intermolecular hydrogen bonding between similar molecules.
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grenade
2061 Points
8 years ago
These deviations are caused due to difference in intermolecular forces of attraction between solute molecules in pure solute, solvent molecules in pure solvent and solute and solvent in a solution
 
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Non ideal solutions showing positive deviation The intermolecular attractive forces between solute-solvent molecules are weaker than those between solutesolute and solvent-solvent molecules i.e. A-B
 
Non ideal solutions showing negative deviation The intermolecular attractive forces between solute-solvent molecules are stronger than those between solute-solute and solventsolvent molecules i.e. A-B > A-A and B-B interactions 
Arkadyuti Chakraborty
11 Points
6 years ago
A solution made of two or more compounds have adhesive and cohesive forces. Cohesive forces are the attractive forces between the same molecules. Adhesive forces are the attractive forces between different molecules of the solution.A real solution shows positive deviation from Raoult`s law when the cohesive forces are stronger then adhesive forces. It shows negative deviation when the adhesive forces are stronger than cohesive forces.

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