Francois-Marie Raoult formulated Raoult’s law, discovered aqueous solutions freezing point

Francois-Marie Raoult – formulated Raoult’s law

Francois-Marie Raoult

Biography & contributions

Francois-Marie Raoult was a French chemist born on May 10, 1830 – died on April 01, 1901. Raoult conducted research into the behavior of solutions, especially their physical properties and formulated the Raoult’s law.

Raoult's name is best known in connection with work on solutions, to which he devoted the last two decades of his life. His first paper describing how solutes depressed the freezing points of solutions was published in 1878. Further experiments with various solvents, such as benzene and acetic acid, in addition to water, led him to believe in a simple relation between the molecular weights of a solute and the freezing-point of a solution.

Raoult worked was that concerning the depression of a solvent's vapor pressure, due to a solute, showing that the decrease is proportional to the solute's molecular weight.

Raoult's freezing-point depression method became even more useful after it was improved by Ernst Otto Beckmann and became a standard technique for determining molecular weights of organic substances.

Freezing-point depression

Freezing-point depression describes the process in which adding a solute to a solvent decreases the freezing point of the solvent. This effect causes sea water, to remain liquid at temperatures below 0 °C (32 °F), the freezing point of pure water.

As a result of freezing point depression, radiators do not freeze in winter (unless it is extremely cold, e.g. −30 to −40 °C. Road salting takes advantage of this effect to lower the freezing point of the ice it is placed on. Lowering the freezing point allows the street ice to melt at lower temperatures. Freezing-point depression is used by some organisms that live in extreme cold. Such creatures have evolved means through which they can produce high concentration of various compounds such as sorbitol and glycerol. Freezing-point depression can also be used as a purity analysis tool when analysed by differential scanning calorimetry. It is also the same principle acting in the melting-point depression observed when the melting point of an impure solid mixture is measured with a melting point apparatus, since melting and freezing points both refer to the liquid-solid phase transition.


In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The solution more or less takes on the characteristics of the solvent including its phase, and the solvent is commonly the major fraction of the mixture.

Raoult's Law

Raoult's law states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture.

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