a) What effect on the boiling point of a liquid is produced by the presence of a

Question

a) What effect on the boiling point of a liquid is produced by the presence of a fully miscible liquid impurity of lower boiling point?

b) When carrying out an atmospheric pressure distillation why is it necessary to have the system vented?

c) You wish to distill a material that is temperature sensitive and decomposes at a temperature lower than its boiling point at atmospheric pressure. This material forms an azeotropic mixture with water. Suggest two methods of distillation appropriate for a successful distillation of this material.

d) You attempt a fractional distillation of a two component mixture but are not successful in obtaining sufficient separation. How would you modify your system to improve separation?

Explanation / Answer

1. a fully miscible liquid impurity can decrease the partial pressure of any liquid over the pure liquid, thus you need higher temperature for the vapor pressure to meet external pressure ( tends to increase the boiling point )

2.The increasing pressure will cause the glass to explode so it is necessary to have the system vented.

3. a) Pressure-swing distillation
b) By using molecular sieves

4. By increasing the surface area inside the column, it gives the maximum possible contact between the liquid trickling down and the hot vapour rising. so in this way we can modify system to improve separation.

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