Intermediate Topic 900 of 1102 Analytical, Lab & Spectroscopy
Steam Distillation
Separating temperature-sensitive compounds by distilling with steam.
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In-depth explanation of Steam Distillation
Steam distillation separates volatile organic compounds that are immiscible with water by passing steam through the mixture, allowing distillation at a temperature below 100 C. Because the compound and water are immiscible, each exerts its own vapour pressure, and the total pressure equals the sum of the two. The mixture therefore boils when this sum reaches atmospheric pressure, at a temperature lower than the boiling point of either component alone. This is valuable for heat-sensitive natural products that would decompose at their normal boiling points. The distillate separates into two layers, from which the organic compound is isolated. The method is widely used in the perfume and flavour industries.
Going deeper: Steam Distillation
Key ideas: Total pressure equals the sum of vapour pressures of water and the oil, so the boiling temperature is lower than 100 C. The mass ratio in the distillate is proportional to vapour pressure times molar mass: m(oil)/m(water) = (P_oil x M_oil)/(P_water x M_water). Use it for compounds that are steam volatile, insoluble in water and stable to hot water.
Common mistakes and connections: A common error is applying steam distillation to a water-miscible compound, where it fails. Another is thinking the mixture boils at the average of the two boiling points. Also, the organic yield is limited because the oil mass fraction in distillate is small, so extraction with an organic solvent often follows. Links to Dalton's law, vapour pressure and solvent extraction.
Visualization of Steam Distillation
Immiscible bromobenzene and water add their vapour pressures, so the mixture boils at about 95 C, below the boiling point of either component alone. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Extracting eucalyptus or lavender essential oils by steam distillation at a temperature below 100 C.
Frequently asked questions about Steam Distillation
What is Steam Distillation?
Separating temperature-sensitive compounds by distilling with steam.
Is Steam Distillation a beginner, intermediate or advanced topic?
Steam Distillation is a intermediate topic in Analytical, Lab & Spectroscopy. It builds on the vocabulary of beginner topics in this area.
What should I learn before Steam Distillation?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Filtration, Distillation, Fractional Distillation.
What comes after Steam Distillation?
The next topics in Analytical, Lab & Spectroscopy are Crystallization and Recrystallization.
Can I practise Steam Distillation with quizzes?
Yes. The interactive lesson includes a self-check question on Steam Distillation, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Steam Distillation fits in Analytical, Lab & Spectroscopy
Steam Distillation is topic 24 of 99 in Analytical, Lab & Spectroscopy.