Question

1) If you allowed your distillation to go a little longer than you did, how do you think the composition data would change?

2) In theory, fractional distillation should give better separation than simple distillation. Does your data support this expectation? Suggest why or why not.

Answer 1

Answer (2)

When heating a mixture of two or more liquids, even with quite different boiling points, some of the heavier liquid will vaporise and contaminate the recovered lighter liquid.
When performing a Simple distillation, you'll find that a second and even a third 'Run' of the recovered liquid each time will be necessary to improve the separation and purity of the distillate.
With Fractional Distillation, the exchange between vaporising, rising vapours and condensing, falling liquids (reflux), performs the extra separation process in a single and continuous operation.
The rising vapour in contact with the liquid on each tray will give up its heavy ends to the liquid on the tray as it rises, and the falling liquid will give up its lighter components to the rising vapour as it bubbles through the liquid flowing across the tray. This interchange continues to take place on each tray in the column, (there is usually a large number of trays). Each tray is, in essence, behaving as a simple distillation process giving multiple separations in one operation. This results in a high purity product from each product offtake.