Hydrocarbons and Its Identification Tests for Classification

Hydrocarbons and Its Identification Tests for Classification ADMC, PMMC, LAC, AKC, RMC, LJMD 2A-Pharmacy, Faculty of Pharmacy, University of Santo Tomas

Abstract Hydrocarbons are the simplest organic compounds containing only elements carbon and hydrogen. These organic compounds can be classified into as to whether they are cyclic or not, saturated or unsaturated, and if they are aliphatic or aromatic. In this experiment, the objective is to identify the compounds’ intrinsic physical properties and chemical properties based on the structure and behaviour, moreover, to differentiate the hydrocarbons with the use of these properties, and to analyse as to whether a hydrocarbon is saturated, actively unsaturated, aromatic or arene. To determine its saturation, solubility test in concentrated sulphuric acid was used and it showed that single-bonded compounds are saturated and unsaturated are the one with double or triple bonds. For, active unsaturation where only cyclohexene was positive Baeyer’s Test and Bromine Test was used. For the nitration, it was a test for aromaticity and only benzene and toluene were aromatic. While for oxidation, it was at test for arene and only toluene was positive. I.

Introduction Hydrocarbons are the simplest organic compounds containing only elements carbon and hydrogen. These organic compounds can be classified into as to whether they are cyclic or not, saturated or unsaturated, and if they are aliphatic or aromatic. Certain properties of these compounds each inherent only to a specific compound help and determine its classification of the compound. It is important to classify these hydrocarbons for they can be of great importance to human being. With these classifications, it is important to uses and purposes to society especially in the field of pharmacy and medicine. We can never ignore the importance of these hydrocarbons for they are part of natural processes present on earth. Examples of these hydrocarbons are natural gases, petroleum, paints and textile which are of importance to human beings. In this experiment, the objective is to identify the compounds’ intrinsic physical properties and chemical properties based on the structure and behaviour and moreover, to differentiate the hydrocarbons with the use of these properties. Also, on a more important note, to analyse as to whether a hydrocarbon is saturated, actively unsaturated, aromatic or arene.

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Materials and Method Hydrocarbons used in this to be analysed in this experiment are hexane, heptane, cyclohexane, cyclohexene, benzene, and toluene which will undergo certain tests for classification. The first step was the identification of its physical state, color, and odor. This was done simultaneously after the collection of sample reagents and must be observed only at room temperature. For this step, the physical state was described as well as the appearance in terms of its colour and if there are cases of turbidness. The odor was described after investigating using the wafting motion. As to its solubility in concentrated sulphuric acid, its solubility was determined with the addition of the sample to an mL of concentrated sulphuric acid. Also, any change in colour and/or warming effect was noted. For the ignition test, 3-5 drops of the liquid sample was placed in an evaporating dish and was lighted using a match. The flammability of the sample was determined. In this test, the colour of the flame as well as if there was a soot formed. To determine its saturation, the Baeyer’s Test and Bromine Test was used. Baeyer’s Test was done by placing five drops of the sample into a dry test tube. Two drops of 2% Potassium

permanganate solution was added. The test tube was shaken vigorously and the rate and extent at which the reagent was decolorized was observed. Decolourization will only be immediate if and only if the decolourization happened within one minute. The formation of brown suspension was also observed. The results of the reaction of water with 2% Potassium permanganate solution was used as the negative control. Bromine test was done by adding 10 drops of 0.5% Br2 in CCl4 reagent in a previously prepared five-drop sample in a dry test tube. Just like the Baeyer’s test, the test tube was vigorously shaken and the rate and extent of the decolourization of the reagent or the bromine colour was discharged was observed. Reaction of 0.5% Br2 in CCl4 reagent with water was used as the negative control. The reaction was exposed to sunlight if the decolourization was not observed within one minute. The sample compound will be categorized as actively unsaturated. In the test for aromaticity, nitration will be used. In the nitration test, a nitrating mixture was prepared. 2mL of concentrated nitric acid

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was placed in an Erlenmeyer flask. While immersed in an evaporating dish with water, 2mL of concentrated sulphuric acid was gradually added. The mixture was then cooled to room temperature. In a dry test tube, 5 drops of the sample was placed in a dry test tube. 8 drops of the nitrating mixture was added and the test tube was shaken to ensure complete mixing. A canary yellow layer must be observed for sample compounds that are aromatic. The mixture was diluted with 20 drops of water. There was a need for water bath for 10 minutes for mixtures with no immediate reaction observed. Basic oxidation is a test for the classification of arenes. In a test tube, four drops of the sample was added with one drop of 2% Potassium permanganate solution, seven drops of distilled water, and three drops 10% Sodium hydroxide solution. The test tubes were placed in water bath for two minutes. A blue-green solution with possibly brown precipitate was observed for some sample compounds.

Results and Discussion Sample Compound Physical State Appearance Odor Hexane Liquid Clear, colourless Gasoline-like Heptane Liquid Clear, colourless Odorless Cyclohexane Liquid Clear, colourless Acetone-like Cyclohexene Liquid Clear, colourless Gasoline-like Benzene Liquid Clear, colourless Plastic balloon-like Toluene Liquid Clear, colourless Gasoline-like Table No. 1. Physical State, Appearance and Odor observed.

For solubility, it follows the like dissolves like rule. Therefore, polar compounds like water, alcohol, and carboxylic acids will only dissolve polar compounds. Likewise, nonpolar compounds will only dissolve nonpolar compounds. In the experiment, miscibility was also determined. Miscibility is the ability to form a homogenous solution in mixing proportion. Homogenous solutions mean that

compounds are soluble in concentrated sulphuric acid. Hydrocarbons tend to be more nonpolar and therefore will only be dissolved in nonpolar compounds. In the experiment, hexane, heptane, and cyclohexane showed miscibility and solubility. These properties depend on the intermolecular forces of attraction. For example, water and ethanol will form a miscible solution due to hydrogen bonding of both compound and

will undergo strong intermolecular attraction. nonpolar due to the dispersion between Alkenes and alkynes are tend to be more molecules. Sample Compound Solubility in concentrated H2SO4 Inference Hexane Soluble (clear, colorless) Saturated Heptane Soluble (clear, colorless) Saturated Cyclohexane Soluble (clear, colorless) Saturated Cyclohexene Miscible (turbid, orange) Unsaturated Benzene immiscible (clear, yellowish) Unsaturated Toluene immiscible (clear, colorless to yellow) Unsaturated Table No. 2. Results for Solubility Test in Concentrated in H2SO4 An organic compound is said to be saturated when it only contains single covalent bonds. Therefore, unsaturated hydrocarbons are those compounds with double or triple covalent bonds. Examples of saturated hydrocarbons are hexane, heptane, and cyclohexane just like the Sample Compound Hexane Heptane Cyclohexane Cyclohexene Benzene Toluene

Ignition Test Orange flame, no soot Orange flame, no soot Orange flame, no soot Orange flame, no soot Orange flame, no soot Orange flame, with soot, violent reaction Table No. 3. Results for Ignition Test

For the ignition test, all of the compounds are flammable but there is a difference in the flame during the experiment. Alkanes react with oxygen and when they react with oxygen heat and light is given off. If oxygen is limited, they to not burn efficiently. Also in the reaction of an alkane with oxygen, the products are carbon dioxide and water, the hydrocarbons will give off carbon monoxide and Sample Compound Hexane

Baeyer’s Test none

Heptane

none

Cyclohexane

none

Cyclohexene

Immediate decolourization none

Benzene

results presented in Table No. 2. Alkane are therefore considered as saturated hydrocarbons. Conversely, cyclohexene, benzene, and toluene are unsaturated hydrocarbons. Alkenes and alkynes fall under this classification of hydrocarbons.

Inference Flammable Flammable Flammable Flammable Flammable Flammable

elemental carbon. That is the reason why there are evidences of soot. For alkenes, they react violently with fire because they have very reactive multiple carbon bonds. Also, toluene showed a violent ignition, aside from the reason that is a reactive multiple carbon bonds, is that it has oxygen present.

Bromine Test Decolorized with sunlight; warming effect Decolorized with sunlight; warming effect No decolourization colourization Decolorized with sunlight; warming effect

Inference Not actively unsaturated Not actively unsaturated Not actively unsaturated Actively unsaturated Not actively unsaturated

Toluene

none

Decolorized with sunlight; Not actively warming effect unsaturated Table No. 4. Results for Baeyer’s Test and Bromine Test

Alkanes can be identified using the Bromine test. The visible positive result for bromine test is the brown precipitate. Alkanes can be identified because it requires light for the reaction to take place. This is evident for hexane, heptane, and cyclohexane. Alkenes and alkynes also react with bromine in CCl4 but there is no need for sunlight for it to complete its reaction. Therefore, hexane, heptane, and cyclohexane are saturated hydrocarbons while

cyclohexene, benzene and toluene are unsaturated hydrocarbons but are not actively unsaturated. Baeyer’s test will determine if a compound if they are unsaturated. Potassium permanganate is a violet solution and when it reacts with unsaturated carbons it will changes color showing a brown precipitate. With this test, it showed that cyclohexene is actively unsaturated.

Sample Compound Nitration Hexane No change Heptane No change Cyclohexane No change Cyclohexene Yellow solution Benzene Yellow oily layer Toluene Yellow oily layer Table No. 5. Results for Test for Aromaticity Nitration Nitration is a chemical reaction in which a nitro group is added to a hydrocarbon compound replacing a hydrogen. In nitration, sulphuric acid and nitric acid are reacted with the samples. Simple aromatic hydrocarbon will react with warm sulphuric acid to form a

Inference aliphatic aliphatic aliphatic aliphatic aromatic aromatic

sulfonic acid which will then dissolve and then precipitate when the nitro group is precipitated. Yellow globules indicate that the hydrocarbon is aromatic which is true for benzene and toluene while the others are aliphatic for there are no visible positive result.

Sample Compound Hexane Heptane Cyclohexane Cyclohexene Benzene Toluene

Basic Oxidation Inference No visible positive result Not an arene No visible positive result Not an arene No visible positive result Not an arene Brown precipitate with visible positive Oxidized but not an result arene No visible positive result Not an arene Blue-green solution arene Table No. 5. Results for Test for Aromaticity Nitration

For this test, a strong oxidizing agent was used which is KMnO4 and this reaction will signify that there is an oxidation reaction formed IV.

References

Indiana University Southeast, Spurlock, D.. (2007). Chemical Reactivity of Hdrocarbons Course

when there is a blue-green solution. Toluene is the one that has a visible positive result and therefore is an arene. Notes. Retrieved from Indiana University Southeast Web site: http://homepages.ius.edu/Dspurloc/c 122/hyd.htm

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Tomas (2014). organic Manila.