Question

A flask contains a mixture of isohexane and $3-\mathrm{methylpentane}$. One of the liquids boils at $63°\mathrm{C}$ while the other liquid boils at $60°\mathrm{C}$. What is the best way to separate these liquids and which one will be distilled out first?

• A. Fractional distillation, isohexane
• B. Simple distillation, $3$-methylpentane
• C. Fractional distillation, $3$-methylpentane
• D. Simple distillation, isohexane

Answer 1

The correct option is A

Fractional distillation, isohexane

1. Fractional distillation is the process by which a mixture of liquids having differences in boiling points less than $70°\mathrm{C}$ can be separated by boiling them.
2. The isohexane boils at $63°\mathrm{C}$ while $3$-methylpentane boils at $60°\mathrm{C}$
3. Hence difference between the boiling points of isohexane and $3$-methylpentane is only $3°\mathrm{C}$ hence fractional distillation is used to separate the two compounds.
4. Simple distillation is the process by which a mixture of volatile and non-volatile liquids or solid-liquid can be separated.
5. In simple distillation, if two liquids are separated then their boiling points are significantly different from each other.
6. Thus, simple distillation cannot be used for separating isohexane and $3$-methylpentane .
7. The boiling point of isohexane is lower than $3$-methylpentane , hence it will be obtained first in fractional distillation.
8. Thus, by fractional distillation, the two liquids can be separated and isohexane is obtained first.
9. Thus, the correct option is A.