Lab# 3 –
Simple and Fractional Distillation
Written by: Theressa Payne
Partner: Jennifer Jantzi
Performed: February 4,2013
February 6, 2013
Lab # 3 – Simple and Fractional Distillation
One of the most important tasks in chemistry is the separation of organic compounds which are not usually found in pure form naturally or as products of chemical synthesis. Distillation is a common method for purifying liquids based upon their boiling points and their differences in vapour pressure. Distillation is a process in which one liquid is separated from another liquid, or a liquid from a non-volatile solid. During the distillation process, the component with the lower boiling point will vapourize first and thereby will travel through the condenser to liquefy in the collection flask before the component of higher boiling point. This process works best when the boiling points of the components are significantly different (simple distillation). Components can be effectively separated by a one-step vaporization. Fractional distillation is used when the boiling temperatures are very similar and the vapour produced is a combination of the mixture. The addition of a fractionating column allows numerous small distillations to occur within the column as the vapour rises towards the condenser.
This experiment will demonstrate the separate a 50:50 mixture of toluene and cyclohexane by two methods and will require two separate equipment setups - one with the fractionating column (fractional distillation) and condenser and one with only the condenser (simple distillation). The results will show the contrast between the two methods and their effeciencies.
See FOL accessed February 3, 2013 and Lab Manual pages 23-32.1,2 Modifications – Use the FOL procedure.
Make sure the thermometer bulb is low enough to achieve good contact with the vapour to be sure of accurate temperature readings. The heating mantle temperature must be watched to maintain continuous boiling within the flask
mp = 111oC
mp = 81oC
Table 1. Observed results of temperature increase of distillation
| Distillation method (oC)
Volume collected (mL)
Chart 1. Graphical Representation of Simple Distillation over Time
Chart 2. Graphical Representation of Fractional Distillation over Time
A) Hexane – Clear, colourless liquid
B) Toluene – Clear colourless liquid
C) Distilled Cyclohexane – Clear, colourless liquid
Upon comparison of the distillation curves of the simple and fractional distillation demonstrate that fractional distillation separates the two compounds more effectively. Simple distillation separates the majority of the two compounds near the beginning and the end of the distilling process, fractional distillation produced much more pure fractions. In simple distillation there is only the condenser column which allows for less surface area for the different compounds to fully separate. Hexane molecules gain higher kinetic energy through boiling faster than the toluene molecules due to their lower molecular weight and lesser intermolecular forces thus hexane has a lower boiling temperature than the toluene. The longer fractionating distillation column as well as the condenser column of the fractional distillation setup allows the higher kinetic energy component (hexane) to separate from the lower-energy toluene...
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