Classification Tests for Hydrocarbons
Authors: Goldie Ann Tejada, Allain Joseph S. Templo, Kristinlyn Trajano, Kevin Viray, Quennie Yu
Group 10, 2F-PH, Faculty of Pharmacy, University of Santo Tomas
The test compounds undergo different physical and chemical tests to differentiate their intrinsic physical properties and chemical properties. Physical state, color, and odor were noted through simple observation. Miscibility of the test compounds were noted through color change or a warming effect. Flammability was tested by igniting 3-5 drops of the sample in a small evaporating dish. Baeyer’s test and Bromine test were used for tests for active unsaturation. Aromaticity of the compound was determined through nitration. Oxidation was tested by introducing 8 drops of 2% KMnO4 solution and 3 drops of 10% NaOH solution to 4 drops of the sample organic compound in a test tube and warming the mixture through water bath. All of the test compounds are liquid and colorless and observed to have a plastic like odor. Miscibility test shows that all of the organic compounds are immiscible and all are flammable. Tests for active unsaturation indicate that hexane, heptane, cyclohexane, benzene and toluene are saturated while cyclohexene is actively unsaturated. Hexane, heptane, benzene, and toluene are classified as aliphatic while cyclohexane, and cyclohexene are aromatic. All are not oxidized except for cyclohexene.
Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons can be aromatic or aliphatic depending on their structure. Hydrocarbons that contain a delocalized ring of pi bonds are called aromatic hydrocarbons and those without a delocalized ring of pi bonds are called aliphatic hydrocarbons. To be classified as Aromatic, a compound must have an uninterrupted cyclic cloud of pi electrons above and below the plane of the molecule and there should be an odd number of pairs of pi electrons in its pi cloud. To be classified as Aliphatic, a compound must have higher hydrogen-to-carbon ratios. Aliphatic hydrocarbons that contain only sigma bonds are called saturated hydrocarbons and those containing both sigma and pi bonds are called unsaturated hydrocarbon. Aliphatic hydrocarbons are divided into 3 classes: alkanes are saturated hydrocarbons that contain only carbon-carbon single bonds. Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. Alkynes are unsaturated hydrocarbons that contain at least one carbon-carbon triple bond. Most hydrocarbons are colorless and odorless. Solubility of organic compounds in H2SO4 indicates whether the sample is a very weak base (can be protonated) or a neutral compound (can’t be protonated). The dissolution of compounds in H2SO4 may also produce large amounts of heat and/or a change in the color of the solution and precipitation; this means that the reaction can be either violent or slow. Ignition test indicates the presence of unsaturation or high carbon to hydrogen ratio. The Degree of luminosity can be assessed by the presence of yellow flame and soot. Aromatic compounds burn with sooty flame due to the incomplete combustion which causes the formation of an unburned carbon. Bayer’s test is a test for double bonds or alkenes. The reagent used for the test is 2% KMnO4. Aromatic compounds show no reation in the test, because of their stability. A positive result for Bayer’s test shows decolorization of a purple solution and formation of a brown precipitate (MnO2). Bayer’s test involves a redox reaction were in Mn7+ is reduced to Mn4+ and alkene is oxidized to a diol. Alkenes react with potassium permanganate (KMnO4) to give a diol and MnO2. Bromine test, like Bayer’s test, is a test for double bonds and aromatic compounds also show no reaction in the test as they are known for their stability. The reagents used are 0.5% Br2 in CCl4. A Positive result...
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