Question
A liquid with high boiling point decomposes on simple distillation but it can be steam distilled for its purification. Explain how is it possible?
✓
Answer
Steam distillation: This type of distillation is essentially a co-distillation with water and is carried out when a solid or liquid, practically insoluble in water, is volatile with steam, possess a vapour pressure of about 10-15 mm of mercury but the impurities are non-volatile. The principle of steam distillation is based on Dalton’s law of partial pressures. Let $p_1$ and $p_2$ be the vapour pressures of water vapour and the organic liquid at the distillation temperature. The liquid boils when total pressure is equal to the atmospheric pressure p, i.e.,
$p=p_1+p_2$ or $p_2=p-p_1$
This process is used in the purification of compounds such as chlorotoluenes, aniline and nitrobenzene. It is also employed in the isolation of essential oils from flowers.
$p=p_1+p_2$ or $p_2=p-p_1$
This process is used in the purification of compounds such as chlorotoluenes, aniline and nitrobenzene. It is also employed in the isolation of essential oils from flowers.
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