Analysis of Hydrocarbons 4

Topics: Hydrocarbon, Benzene, Carbon Pages: 5 (1187 words) Published: December 13, 2008
Analysis of Hydrocarbons

Jennifer Alambra, Ma. Nancy Anulat, Alfonso Apepe*, Jacqueline Arsenal 3Bio4 Department of Biological Sciences - College of Science, University of Santo Tomas, Manila

The unknown hydrocarbon sample was differentiated and characterized by the use of three tests. The outcomes of these tests are as follows: Nitration test (negative), Bromine test (positive) and Basic Oxidation test (positive). From these results the unknown sample can be classified as non-aromatic and unsaturated.


Hydrocarbons are organic compounds that consist of only C and H atoms. They include the alkanes, alkenes, alkynes, and aromatic hydrocarbons. Because of their relatively non-polarity, all hydrocarbons are insoluble in water. When hydrocarbons burn in sufficient oxygen, carbon dioxide and water are the sole products. The main structural difference among hydrocarbon families is the presence of double or triple bonds between carbon atoms. The alkanes are saturated organic compounds, or those with only single bonds. Unsaturated organic compounds are those which have double or triple bonds. [1]

Many common natural substances, e.g., natural gas, petroleum, and asphalt, are complex mixtures of hydrocarbons. The coal tar obtained from coal by coking is also a mixture of hydrocarbons. Natural gas, petroleum, and coal tar are important sources of many hydrocarbons. These complex mixtures can be refined into simpler mixtures or pure substances by fractional distillation. During the refining of petroleum, one kind of hydrocarbon is often converted to another, more useful kind by cracking. Useful hydrocarbon mixtures include cooking gas, gasoline, naphtha, benzene, kerosene, paraffin, and lubricating oils. Many hydrocarbons are useful as fuels; they burn in air to form carbon dioxide and water.

The hydrocarbons differ in chemical activity. The alkanes are unaffected by many common reagents, while the alkenes and alkynes are much more reactive, as a result of the presence of unsaturation (i.e., a carbon-carbon double or triple bond) in their molecules. Many important compounds are derived from hydrocarbons, either by substitution or replacement by some other chemical group or element of one or more of the hydrogen atoms of the hydrocarbon molecule, or by the addition of some element or group to a double or triple bond (in an unsaturated hydrocarbon). Such derivatives include alcohols, aldehydes, ethers, carboxylic acids, and halocarbons. [2]

This experiment aims to differentiate various types of hydrocarbons by the use of different chemical reaction tests. An unknown hydrocarbon sample will be provided and will be characterized through parallel chemical tests (Chemical Analysis)


The first test for chemical analysis of the unknown hydrocarbon is the Nitration test. This reaction will test for aromatics and the mechanism for this reaction is the Electrophilic Aromatic Substitution Reaction where an aromatic ring will easily substitute one of its hydrogen with another larger electrophilic substituent. In this case the electrophile is the NO2+ and the positive reaction is the presence of yellow globules[3]. Toluene (positive standard) is an aromatic ring with a methyl substituent therefore; it will readily react with the agent and will produce the positive visible result, while Hexane (negative standard) is an alkane therefore very much unreactive. In this test, the unknown sample did not produce the desired yellow globule. Therefore, it is non-aromatic.

The next test conducted is the Bromine test. In the bromine test, the presence of unsaturated hydrocarbons (hydrocarbons with double or triple bonds) is determined and it is evident from the disappearance of the reddish brown color of the bromine solution. The bromine adds to double bonds to form the dibromoethane-substituted species[4]. Dibromomethane is a colorless liquid. [see reaction in...
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