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Question

What type of deviation from Raoult's law is exected?
(a) when equal volume of acetone and ethanol is mixed?
(b) when equal volume of acetone and chloroform is mixed?


Solution

Raoult’s law suggests that the partial pressure of each substance above a solution is proportional to its mole fraction x, thus $$p=p^{ 0 }x$$ where $$p^{ 0 }$$ is the vapour pressure of the pure substance.
a) An acetone-ethanol hydrogen bond stronger than an acetone-acetone hydrogen bond. If the reason for the positive deviation of the ethanol/acetone solution is that the H bonds there are weaker than ethanol-ethanol H bonds, then there wouldn't that imply that acetone/water solutions would also have a positive deviation, as water-water H bonds must be much stronger than water-acetone.
b) Experimentally there are deviations from Raoult’s law and they can be in both the ‘positive’ and ‘negative’ direction. A positive deviation means that p is greater than expected from Raoult’s law and thus a negative deviation has pressure that is less than expected. Alcohol/water mixtures show positive deviations and for example acetone/chloroform negative deviations.
The reason for these deviations is due to the different interaction between the molecules. The change in interaction on adding one liquid to another is due to the difference in interaction energies between them, thus if the energies between the same type of molecules of type 1 and 2.

Chemistry

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