Question

An organic liquid vaporizes at a temperature___________ its boiling point in steam distillation.
A.Above
B.Below
C.Equal to
D.None of the above

Answer 1

Hint Boiling point is a point where both liquid and vapor phases are in equilibrium with each other. this point arrives when the vapor pressure of the solution becomes equal to the atmospheric pressure. Lower the vapor pressure higher will be the boiling point and reverse is also true.

Complete step by step:
Boiling point is always a fixed point at a particular pressure. If we change the value of external pressure then boiling point will also change. Now in steam distillation, the mixture that has water and organic compounds is boiled. As we know that boiling point will arrive when the total pressure of mixture became equal to the atmospheric pressure that is:
\[{{\text{P}}_{{\text{atm}}}} = {{\text{P}}_{{\text{water}}}} + {{\text{P}}_{{\text{organic compound}}}}\]
But the vapor pressure of water is considerably higher than that of the organic liquid, so the whole mixture will have a higher vapor pressure due to higher vapor pressure of water. Now the higher the vapor pressure of the mixture is, the easier it would be to match the atmospheric pressure hence boiling point will arrive early. Due to the presence of water with organic compounds the boiling point of organic compounds will get lower.

So the correct option is B.

Note Steam distillation is a separating process in which water along other components are taken. It is also a very good method of purification of substance. It is often used in extraction of essential oils such as eucalyptus oil, camphor oil and orange oil.