Question

A steam volatile organic compound which is immiscible with water has a boiling point of 250°C. During steam distillation, a mixture of this organic compound and water will boil:

• A. above 100°C but below 250°C
• B. above 250°C
• C. at 250°C
• D. close to but below 100°C

Answer 1

Answer: (D)

close to but below 100°C

Answer 2

In steam distillation , a mixture ofimmiscible 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.