Simple Distillation: Separation of Hexane and Toluene

Simple Distillation: Separation of Hexane and Toluene
By: Jessica Hauger

Abstract: The purpose of this experiment is to separate a mixture of hexane and toluene by collecting fractions through simple distillation. Because hexane’s boiling point is about 69°C and the boiling point of toluene is 111°C, the two compounds distill at different times. The distillation took place in a simple distilling apparatus. The refractive index was measured using an Abbé refractometer. After collecting only two fractions and recording the refractive index of each fraction, the percentage of toluene and hexane could be calculated. The first fraction, taken from 60°C to 68°C, contained 89.85% hexane and 10.15% toluene. The other fraction that was collected consisted of 7.28% hexane and 92.72% toluene. Because the boiling point of hexane is so much smaller than that of toluene, the second fraction consisted mostly of toluene.

Structure:

Procedure: Reference pages 10 through 11 titled Simple Distillation: Separation of Hexane and Toluene in the Organic Chemistry Lab Manual posted to blackboard by Dr. Kelly. Omit the collection of a second distillate. Add the collection of the third fraction through cooling of the remaining liquid and collection of that.

Results:

Calculations:

Refractive Index = X(1.3746) + (1-X)(1.4968)

Refractive Index = 1.4968 – 0.1222X

First Fraction:

1.3871=1.4968 – 0.1222X

X = .8985

89.58% hexane

1-0.8985 = 0.1015

10.15% toluene

Second Fraction:

1.4879 = 1.4968 – 0.1222X

X = .0728

7.28% hexane

1 – .0728 = .9272

92.72% toluene

Boiling point difference:

111ºC – 69ºC = 42ºC

Conclusions and Discussions:

Simple distillation, when used to separate two substances, is used mostly when those two substances have boiling points approximately 40ºC apart. The difference between toluene, with a boiling point of 111ºC and hexane, with a boiling point of 69ºC, is 42ºC, making these two substances most easily separated by simple distillation. Distilled between 60ºC and 68ºC, the first fraction collected contained 89.85% hexane and 10.15% toluene. This concurs with the boiling points of the two substances because hexane has such a lower boiling point than toluene. Because of this, most of the toluene was distilled in the first fraction. After attempting to heat and distill the rest of the solution for some time, the most efficient method to get another fraction was to cool the mixture and extract the rest of the solution into a new clean test tube. This fraction contained 7.28% hexane and 92.72% toluene. Basically, the hexane had mostly distilled in the first fraction. Compared to the results of my colleagues, my results were fairly normal, perhaps even more precise than others, with the exclusion of the inability to collect a second fraction.

The main error in this procedure was the inability of the solution to heat up above 68ºC. An overly swift heating of the mixture for the first fraction could have contributed to this. Because the hexane had mostly distilled in the first fraction, the second fraction obtained through cooling and direct extraction without distillation was almost completely toluene. These results were not abnormal, despite not obtaining the second or third fractions correctly, if at all.

Editor’s note (October 23, 2026): The student’s data and calculations are left as written. Three points need correcting.

• The first fraction was mostly hexane, not toluene. The discussion says “most of the toluene was distilled in the first fraction,” but the results show that fraction was 89.85% hexane and only 10.15% toluene. Hexane, the lower-boiling liquid, came off first, and the liquid left in the flask was mostly toluene (92.72%).
• The first-fraction figure is 89.85% hexane, not 89.58%. In the calculations, “89.58% hexane” swaps two digits: the line above it gives X = .8985, and 1 – 0.8985 = 0.1015 matches the 10.15% toluene. Working the equation from the recorded 1.3871 gives X ≈ 0.8977, a little lower; .8985 matches a reading of 1.3870. Either way, the fraction was about 90% hexane.
• A 42°C gap gives only a partial separation. Guidelines vary on how far apart boiling points should be for simple distillation. LibreTexts says it’s used when they differ by more than about 100°C and won’t fully purify closer mixtures (LibreTexts, Overview of Distillation). That fits these results: even the first fraction held about 10% toluene.

How refractive index tracks the separation

Refractive index (n) compares the speed of light in a vacuum with its speed in a substance, n = c/v (OpenStax, The Law of Refraction). Pure hexane and toluene have different values (1.3746 and 1.4968 above), and the calculation assumes a mixture’s reading falls on a straight line between them. In a simple distillation the distillate is always enriched in the lower-boiling compound (LibreTexts), so hexane (boiling point about 69°C) dominated the first fraction and toluene (about 111°C) was left behind (NIST: hexane, toluene). For a similar lab that separates cyclohexane and toluene by both simple and fractional distillation, see Simple and Fractional Distillation.

Further reading: The Organic Chem Lab Survival Manual (11th ed.) by James W. Zubrick — a practical guide to setting up a simple distillation, placing the thermometer and using an Abbé refractometer, the techniques used in this lab.
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