Determination of a Boiling Point: Simple and Fractional Distillation

Introduction

The boiling point of a substance is a useful physical property for the characterization of pure compounds. A common method for the determination of boiling points as well as separating and purifying volatile liquids, is distillation, which makes use of the specific boiling points, of the liquid components in the mixture. When there is only one volatile compound, or when one of the liquids has a boiling point well below the others, a simple distillation is used. However, if there are two or more liquid components, which have boiling points near each other, a fractional distillation must be used.

Using simple distillation, you will separate toluene from a non-volatile dye. Then, using a fractional distillation apparatus, you will separate toluene and cyclohexane. While performing the distillation, you will monitor the temperature that the volatile liquid has, in the gas phase, using the Vernier Wide-Range Temperature Probe. This temperature should remain constant as each distillate is being condensed, and actually represents the boiling point of this chemical. To confirm the presence of each compound, you will measure the density of your distillates.

Objectives

In this experiment, you will

  • Assemble and perform a simple distillation of toluene.
  • Assemble and perform a fractional distillation to isolate toluene and cyclohexane.
  • Produce a graph of time vs. temperature for each distillation.
  • Determine the density of each purified compound.
  • Identify an unknown compound based on boiling point and density.

Sensors and Equipment

This experiment requires each of the following Vernier sensors and equipment (unless otherwise noted):

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

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  • Step-by-step instructions for computer and LabQuest data collection
  • List of materials and equipment

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Standards Correlations

No standards correlations for this experiment.

Experiment 3 from Organic Chemistry with Vernier Lab Book

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Vernier lab books include a CD with word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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