In steam distillation, a mixture of immiscible liquids boils at a temperature lower than the boiling point of either individual component. This occurs because the total vapor pressure of the mixture is the sum of the vapor pressures of the individual components. The mixture boils when the total vapor pressure equals the atmospheric pressure. Since the organic compound is steam volatile (meaning it has a significant vapor pressure even below its boiling point) and immiscible with water, it will co-distill with water at a temperature close to, but slightly below, the boiling point of water (100$^\circ$C). The boiling point will be slightly below 100$^\circ$C due to the contribution of the organic compound's vapor pressure to the total vapor pressure.
List I | List II | ||
---|---|---|---|
A | Mesozoic Era | I | Lower invertebrates |
B | Proterozoic Era | II | Fish & Amphibia |
C | Cenozoic Era | III | Birds & Reptiles |
D | Paleozoic Era | IV | Mammals |