Explain non-ideal solutions and the occurrence of positive and negative deviations in non-ideal solutions.
(N/A) non-ideal solution is one that does not obey Raoult's law over the entire range of concentration.
The vapour pressure of such a solution is either higher or lower than that predicted by Raoult's law. If it is higher,the solution exhibits positive deviation,and if it is lower,it exhibits negative deviation from Raoult's law.
Positive Deviation:
In this case,$A-B$ interactions are weaker than those between $A-A$ or $B-B$. The intermolecular attractive forces between solute-solvent molecules are weaker than those between solute-solute and solvent-solvent molecules. Consequently,molecules of $A$ (or $B$) escape more easily than in the pure state,increasing the vapour pressure.
Example: Mixtures of ethanol and acetone.
Negative Deviation:
In this case,$A-B$ interactions are stronger than those between $A-A$ or $B-B$. The intermolecular attractive forces between solute-solvent molecules are stronger than those between solute-solute and solvent-solvent molecules. This decreases the tendency of molecules to escape,lowering the vapour pressure.
Example: Mixtures of phenol and aniline or chloroform and acetone.
The vapour pressure of such a solution is either higher or lower than that predicted by Raoult's law. If it is higher,the solution exhibits positive deviation,and if it is lower,it exhibits negative deviation from Raoult's law.
Positive Deviation:
In this case,$A-B$ interactions are weaker than those between $A-A$ or $B-B$. The intermolecular attractive forces between solute-solvent molecules are weaker than those between solute-solute and solvent-solvent molecules. Consequently,molecules of $A$ (or $B$) escape more easily than in the pure state,increasing the vapour pressure.
Example: Mixtures of ethanol and acetone.
Negative Deviation:
In this case,$A-B$ interactions are stronger than those between $A-A$ or $B-B$. The intermolecular attractive forces between solute-solvent molecules are stronger than those between solute-solute and solvent-solvent molecules. This decreases the tendency of molecules to escape,lowering the vapour pressure.
Example: Mixtures of phenol and aniline or chloroform and acetone.
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$A$ solution of acetone in ethanol:
$1 \, \text{mole}$ of liquid $A$ and $2 \, \text{mole}$ of liquid $B$ form a solution with a vapor pressure of $38 \, \text{torr}$. If the vapor pressures of pure $A$ and pure $B$ are $45 \, \text{torr}$ and $36 \, \text{torr}$ respectively,the solution will be:
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View SolutionTotal vapour pressure of a mixture of $1 \, mol \, X$ $(P_x^o = 150 \, torr)$ and $2 \, mol \, Y$ $(P_y^o = 300 \, torr)$ is $240 \, torr$. In this case:
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View SolutionWhich property is shown by an ideal solution?
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View SolutionWhich of the following form an ideal solution?
$I$. Chloroethane and bromoethane
$II$. Benzene and toluene
$III$. $n$-hexane and $n$-heptane
$IV$. Phenol and aniline
$I$. Chloroethane and bromoethane
$II$. Benzene and toluene
$III$. $n$-hexane and $n$-heptane
$IV$. Phenol and aniline
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