Fractional Distillation and GC Analysis of Hydrocarbon Mixtures

Abstract

An introductory experiment involving the fractional distillation of a three-component hydrocarbon mixture and analysis of the recovered fractions by gas chromatography is described. It has been used in a general chemistry sequence that includes a section on organic chemistry, but it is also well suited for an introductory organic chemistry laboratory course. The hydrocarbon mixtures are given to student groups as unknowns. They contain an alkane or cycloalkane, an alkene or cycloalkene, and an alkyl-substituted aromatic hydrocarbon. Five unknown mixtures are analyzed by the lab class. Supplied with the following information, the students identify the three species in their mixture: the names, structures and boiling points of all 15 hydrocarbons used to make the five unknowns; the IR and 13C NMR spectra of each of the three species in their particular unknown; and the experimentally determined boiling points. Representative GC results from student fractional distillations are included. This lab experiment is part of an effort to develop a general chemistry sequence for engineering students involving active learning and using the theme of "Chemistry and the Automobile".

Electroless Deposition on Three Substrates: Brass Washers, Cicada Exoskeletons, and Beetles

“…This experiment also represents an ongoing effort by one of us (C.J.D.) to develop lab experiments that showcase applied chemistry. − These lab experiments support a two-semester general chemistry sequence populated exclusively by undergraduate engineering students that employs the overarching theme of Chemistry and the Automobile , which has been previously described in this Journal …”

“…4−10 These lab experiments support a two-semester general chemistry sequence populated exclusively by undergraduate engineering students that employs the overarching theme of Chemistry and the Automobile, which has been previously described in this Journal. 4…”

Contribution of Benchtop NMR Spectroscopy to the Identification of Unknown Liquids Separated by Fractional Distillation

“…It allows students to experience the purification of liquids 3 , the separation of unknown mixtures 1,4,5 and even the understanding of the Le Châtelier principle through reactive distillation 6 . Advanced structural characterization techniques like GC-MS or high field NMR spectroscopy are sometimes employed to characterize the distillate [4][5][6] . However, these techniques are not commonly available in the teaching laboratory for obvious cost reasons.…”

“…Among the purification techniques available for organic compounds (i.e., recrystallization, liquid–liquid extraction, silica gel flash column chromatography), fractional distillation is commonly taught in undergraduate practical work sessions. , It allows students to experience the purification of liquids, the separation of unknown mixtures, ,, and even the understanding of the Le Châtelier principle through reactive distillation . Advanced structural characterization techniques like GC–MS or high-field NMR spectroscopy are sometimes employed to characterize the distillate. − However, these techniques are not commonly available in the teaching laboratory for obvious cost reasons.…”

Implementation of an Accessible Gas Chromatography Laboratory Experiment for High School Students

“…GC analysis does not depend on advanced knowledge of bonding or structure, and the quantitative analysis used with GC data is similar to the methods employed by professional chemists. In our implementation of the GC experiment, we avoid hazardous chemicals, expensive instruments, and complex data analysis in previously published experiments for college-level courses. − Our experiment uses air-fed Vernier Mini GC Plus instruments, which are small, relatively inexpensive (ca. $2000), and portable (see Supporting Information for specifications). , These simple GC instruments have detectors that cannot accommodate water or amines and are restricted to compounds with boiling points lower than 200 °C at atmospheric pressure .…”