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.
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