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Solutions — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistrySolutions3 Marks
Question
Explain positive deviation from Raoult's law with an example.
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Answer

When the is a positive deviation in the mixture of two liquids A and B, the A-B attraction is weaker than the attraction between A-A and B-B, that is, in this situation the intermolecular force between the solute solvent molecules is less than that of the solute-solute and solvent-solvent molecules. Therefore, form such solutions, molecules of A and B can escape more easily than the pure component, due to whih the vapour pressure increases.
Example: Mixture of pure ethanol and acetone, there are hydrogen bonds between the molecules. When acetone is added to pure ethanol, its molecules comes between the hydrogen bonds of ethanol molecule and breaks them. Due to this intermolecular forces of attraction, this mixture shows positive deviation from Raoult's law.

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