Question

3. You are hard at work, setting up the apparatus to separate a 40:60 mixture of diethyl ether and toluene by simple distillation. Just as you are getting ready to begin the experiment, your lab partner mistakenly adds a small amount of sodium sulfate into the distillation flask. Would simple distillation still be appropriate or should you switch to fractional distillation? Explain.

Answer 1

In simple distillation, the vapor is immediately channeled into a condenser. Consequently, the distillate is not pure but rather its composition is identical to the composition of the vapors at the given temperature and pressure. That concentration follows Raoult's law.

As a result, simple distillation is effective only when the liquid boiling points differ greatly (rule of thumb is 25 °C) or when separating liquids from non-volatile solids or oils. For these cases, the vapor pressures of the components are usually different enough that the distillate may be sufficiently pure for its intended purpose.

For many cases, the boiling points of the components in the mixture will be sufficiently close thatRaoult's law must be taken into consideration. Therefore, fractional distillation must be used in order to separate the components by repeated vaporization-condensation cycles within a packed fractionating column. This separation, by successive distillations, is also referred to as rectification.

As the solution to be purified is heated, its vapors rise to the fractionating column. As it rises, it cools, condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors are determined once again by Raoult's law. Each vaporization-condensation cycle (called a theoretical plate) will yield a purer solution of the more volatile component. In reality, each cycle at a given temperature does not occur at exactly the same position in the fractionating column; theoretical plate is thus a concept rather than an accurate description.

More theoretical plates lead to better separations. A spinning band distillation system uses a spinning band of Teflon or metal to force the rising vapors into close contact with the descending condensate, increasing the number of theoretical plates.

nOW Basing on this, the boiling point of diethyl ether is 34.6 ºC and toluene is 111 ºC there is a lot of difference between those points, and sodium sulfate has a way high melting and boiling point (beyond 1000 ºC), it's just a salt, an inorganic salt and it's not soluble on these mixture,so, even when it's there, the mixture would distillate at the same point, so a simply distillation may work.

Hope this helps.