Analysis of Hydrocarbons

Leonise Gelito, Godwin Evan Halfon*, Antonio Hernandez, and Jose Carmelo JavierDepartment of Chemistry, University of Santo Tomas, Manila, Philippines

Abstract

The objectives of this experiment entitled, “Analysis of Hydrocarbons", are to

differentiate various types of hydrocarbons; to device a scheme to distinguish

hydrocarbons from each type; and to characterize an unknown hydrocarbon through

parallel chemical tests. Hydrocarbons are divided into Aliphatic (saturated or

unsaturated) and Aromatic (with or without sidechain). Chemical Analysis is a foolproof

way of correctly evaluating the reaction of an unknown sample to a given chemical test

with the use of reference standard. The reference standards used for this experiment

were Hexane, Cyclohexane, Naphthalene and Toluene. There are also three tests

utilized to characterize the unknown sample, which are the Nitrate, Bromine and

Permanganate tests.

Introduction

Hydrocarbons are the simplest organic compounds. Containing only carbon and

hydrogen, they can be straight-chained, branched chain, or cyclic molecules. Carbon

tends to form four bonds in a tetrahedral geometry. Hydrocarbon derivatives are formed

when there is a substitution of a functional group at one or more of these positions.

Hydrocarbons are usually of general use by utilizing chemical reactions that are either

classified as addition or bond-rupture reactions.

Four different hydrocarbons are usually the most common subject to test for the

analysis of hydrocarbons. These are the Hexane, Cyclohexane, Naphthalene and

Toluene. These four are also classified to different types of hydrocarbons, which are the

Saturated Aliphatic Hydrocarbons, Unsaturated Aliphatic Hydrocarbons, Alkylated

Aromatic Hydrocarbons and Non-alkylated Aromatic Hydrocarbons. Refer to Figure 1.

Saturated Aliphatic Hydrocarbon

Hexane

Unsaturated Aliphatic Hydrocarbon

Cyclohexane

Aromatic without Side Chain

Naphthalene

Aromatic with Side Chain

Toluene

Figure 1: Hydrocarbons

Results and Discussions

Four different hydrocarbons were subjected to different in order to differentiate

and analyze what type of hydrocarbon are the samples. The observed results of the

tests are shown in Table 1.

Class of

HydrocarbonSample Nitration Test Bromine Test

Permanganate

Test

Saturated

AliphaticHexane

Clear pink color

(-)

Orange color

(-)

Purple color

(-)

Unsaturated

AliphaticCyclohexane

Rusty dark red color

(-)

Clear colorless

(+)

Brown precipitate

(+)

Aromatic

without side

chain

NaphthaleneYellow precipitate

(+)

Clear red color

(-)

Purple color

(-)

Aromatic with

side chainToluene

Yellow precipitate

(+)

Yellow color

(-)

Purple color

(-)

Table 1: Observed results in the experiment

In the Nitration Test, concentrated

H2SO4 and concentrated HNO3 with 1:1 ratio

was used as the nitrating reagent. This test will

give a positive result for the Aromatic

Hydrocarbons. The positive result will be determined if the reaction shows a yellow oil or

yellow precipitate.

In the Bromine Test, 5% Br2 in CH2Cl2

was used as the reagent. This test will give a

positive result for Unsaturated Hydrocarbons.

The positive result will be determined if the

solution in the reaction decolorizes or changes

to a colorless liquid.

In the Permanganate Test, 0.1%

aqueous KMnO4 and 10% NaOH were used as

the reagents. This test will give a positive

result for Alkylated Hydrocarbons or Aromatic

Hydrocarbons with side chain. The positive result will be determined if the reaction

shows a brown precipitate.

Tests Reagents Positive for Visible Result

Nitration1:1

conc. H2SO4 and conc. HNO3

Aromatic Hydrocarbons Yellow oil or precipitate

Bromine 5% Br2 in CH2Cl2Unsaturated

Hydrocarbons

Decoloration of solution

(colorless)

Permanganate0.1% aq. KMnO4

10% aq. NaoH

Alkylated Aromatic

HydrocarbonsBrown precipitate

Table 2: Summary of the results

Figure 2: Nitration of Naphthalene

Figure 3: Nitration of Toluene

Figure 4: Bromination of Cyclohexane

Figure 5: Toluene in KMnO4

Figure 6: Schematic Analysis of Hydrocarbons

Experimental

Nitration Test: Ten drops each of the sample were placed in four separate test tubes. Then ten drops of the nitrating reagent were added to each of the sample. The mixtures were shaken and placed in a hot water bath for 5 minutes. 20 drops of distilled water were added to each of the test tubes. And lastly, the observations were recorded.

Bromine Test: Ten drops each of the sample were placed in four separate test tubes. Then ten drops of the bromine reagent were added to each of the sample. The mixtures were shaken and the observations were recorded.

Permanganate Test: Ten drops each of the sample were placed in four separate test tubes. Then five drops of 0.1% of KMnO4 and five drops of 10% NaOH were added to each of the sample. The mixtures were shaken and placed in a hot water bath for 2 minutes. And lastly, the observations were recorded.

References

Klein, D., (2012). Organic Chemistry. USA: John Wiley & Sons Inc.

R.J. Fesseden and J.S. Fesseden, Organic Chemistry, 4th Edition, California, U.S.A,

Pacific Grove, 1990, Pages 103, 431, 477.

Michelle, J. Sienko, Robert A. Plane, Chemistry, 5th Edition, London, McGraw-Hill Book

Company, 1981, Pages 455-465.

Hydrocarbons

Aliphatic

Saturated Unsaturated

Aromatic

Alkylated Non-alkylated