Tag: Solutions

Physical Chemistry · Solutions Osmotic Pressure and the van’t Hoff Factor The most sensitive of the colligative properties, and the only one practical for measuring the molar mass of very large molecules. BSc & MSc · Physical Chemistry · Concept The short answer: Osmotic pressure is the pressure that must be applied to stop solvent flowing through a semipermeable membrane into a solution. It is far larger than the other colligative effects at the same concentration, which is why it is the method of choice for polymers and proteins. The van’t Hoff factor corrects for dissociation or association of the…

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Physical Chemistry · Solutions Ideal and Non-Ideal Solutions: Raoult, Henry and Azeotropes Deviations from ideality are not an inconvenience — they are the reason azeotropes exist, and the sign of the deviation predicts which kind forms. BSc & MSc · Physical Chemistry · Concept The short answer: An ideal solution obeys Raoult’s law across the whole composition range, which requires the interactions between unlike molecules to match those between like ones. Where unlike interactions are weaker, the solution shows positive deviation and can form a minimum boiling azeotrope; where stronger, negative deviation and a maximum boiling azeotrope. Raoult’s law and…

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