Question

1. What experimental difficulty would you encounter if you had neglected to include a drying step before evaporating the ether solution of the neutral organic compound?

1b. An extraction procedure specifies that an aqueous solution containing dissolved organic material be extracted twice with 10-mL portions of diethyl ether. A student removes the lower layer after the first extraction and adds the second 10-mL portion of ether to the upper layer remaining in the separatory funnel. After shaking the funnel, the student observes only one liquid phase with no interface. Explain.

Answer 1

1. It is very important to carry out drying step (using various drying agentslike MgSO₄ and CaCl₂) before evaporating ether solution especially because ether has a tendency to dissolve water in it. the drying process is intended to remove this water. If drying is not done, then water is retained and even after evaporation of ether, water will remain in system. This may interact with neutral compound and change its properties and nature. Thus it is very essential to completely dry before evaporating ether.

2.When aqueous solution is extracted using ether, the lower layer is composed of water and top layer is composed of ether since ether is less dense than water. Thus when student removes lower layer, he/she has removed water layer. When second portion of 10 mL ether is added to upper layer (which is nothing but ether layer), it means that ether has been added again to ether layer. Therefore, on shaking the whole phase is monophasic in nature  and there is no separation of phases or interface.