Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam d

step 1 In steam distillation water and organic substance vaporize together and total vapor pressure bec

Explain, why an organic liquid vaporises at a temperature...

Key Concepts

Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the external atmospheric pressure. In a steam distillation setup involving immiscible liquids, the total vapor pressure becomes the sum of the individual vapor pressures. This additive effect means that the mixture reaches the boiling condition at a temperature lower than the boiling point of the pure organic compound, enabling vaporization at reduced temperatures.

Immiscibility

Immiscibility refers to the inability of two liquids to mix into a homogeneous solution. In steam distillation, the organic liquid is typically immiscible with water, which means they form separate layers. This separation allows the vapor pressures to be considered independently, and according to Dalton’s law, their sum leads to the lowering of the effective boiling point of the mixture, ensuring that the organic vapour can be collected at a reduced temperature.

Steam Distillation

Steam distillation is a separation technique used primarily for compounds that are immiscible with water. In this process, the vapor pressures of water and the organic component add together, allowing the mixture to boil at a temperature lower than the boiling point of the organic liquid alone. This method is particularly useful for isolating heat-sensitive compounds since the distillation occurs at a lower temperature than would be required if the organic compound were distilled by itself.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature. In the context of steam distillation, the organic liquid contributes its own vapor pressure alongside the vapor pressure of water. When these pressures sum to equal the external atmospheric pressure, the mixture boils, even if the individual vapor pressure of the organic liquid is below what would normally be needed for its boiling point.

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