REQUEST FOR PRACTICUM INDUSTRY ADVISER

CHM142L Organic Chemistry 1 Laboratory 3rd Quarter SY 2014-2015

Preparation and Characterization of HydrocarbonsMiranda, Marilyn1, Ayson, Jose Paolo, L21Professor, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; 2Student (s),CH142L/A31, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology

ABSTRACT

The objectives of this experiment are to differentiate alkanes, alkenes, alkynes and aromatic hydrocarbons through their properties, to visualize the characteristic reactions of alkanes, alkenes, alkynes and aromatic hydrocarbons, and to prepare acetylene gas. Hydrocarbons are compounds that contain carbon and hydrogen atoms only. They are generally classified as alkanes, alkenes, alkynes and aromatic. Hydrocarbons may be differentiated in terms of their physical and chemical properties. In the experiment, we performed certain tests to distinguish hydrocarbons. Flammability test was the first test we performed for the test compounds namely cyclohexane, cyclohexene and benzene. The second test was solubility which all hydrocarbons are insoluble in water. We observe the reaction of the test compounds in bromination, oxidation and sulphuric acid test. Preparation and test of properties of acetylene was also performed in the experiement. Unsaturated compounds are compounds that have carbon-carbon multiple bonds and produce soot when ignited. Also, hydrocarbons are insoluble in water since they are nonpolar compounds and they cannot form hydrogen bonds. Acetylene is a linear molecule, all four atoms lying along a straight line. Concepts and relationship of hydrocarbons were learned and observed in this experiment.Keywords: hydrocarbons, alkanes, alkenes, aromatic, saturated, unsaturated, bromination, oxidation, acetylene, flammability

INTRODUCTION

The purposes of this experiment are to differentiate alkanes, alkenes, alkynes and aromatic hydrocarbons through their properties, to visualize the characteristic reactions of alkanes, alkenes, alkynes and aromatic hydrocarbons, and to prepare acetylene gas. Hydrocarbons are compounds that contain carbon and hydrogen atoms only. They are generally classified as alkanes, alkenes, alkynes and aromatic. Hydrocarbons may be differentiated in terms of their physical and chemical properties. Among the more useful physical properties that distinguish hydrocarbons are flammability and solubility. They are extremely important to our society because so many products are derived from them: fuels, fabrics, plastics, antifreezes, anaesthetics, insecticides, to name a few. The major source of aliphatic hydrocarbons is petroleum, an extremely complex mixture of compounds. Each of us, on the average, uses several tons of petroleum each year (directly or indirectly), mostly for fuel. Aromatic hydrocarbons are mainly obtained from coal, although small amounts are also obtained from petroleum.

The physical properties of alkenes and alkynes are generally similar to those of alkanes or cycloalkanes with equal numbers of carbon atoms. Alkynes have higher boiling points than alkanes or alkenes, because the electric field of an alkyne, with its increased number of weakly held electrons, is more easily distorted, producing stronger attractive forces between molecules.Aromatic compounds are cyclic compounds in which all ring atoms participate in a network of pi bonds, resulting in unusual stability. They are less reactive than alkenes, making them useful industrial solvents for nonpolar compounds. Aromatic compounds, originally named because of their fragrant properties, are unsaturated hydrocarbon ring structures that exhibit special properties, including unusual stability, due to their aromaticity.MATERIALS AND METHODS

The experiment was a class performance, we first test the flammability of the test compounds namely cyclohexane, cyclohexene and benzene. Two drops of the test compounds was place in an evaporating dish. The compounds were ignited using a match as shown in figure 1. The observations were noted.FIGURE 1: IGNITING THE COMPOUNDS

The second property was solubility, two drops of each of the test compound was placed in separate micro test tubes. 1 ml of distilled water and was shake. The observations were recorded.

FIGURE 2: TEST FOR SOLUBILITY

After the test for the physical properties, the second part of the experiment was the reactions of alkane, alkene, and aromatic hydrocarbons. The first part was bromination, 2 drops of each of the test compounds was placed in separate micro test tubes. 1.0 M bromine in CCl4 was added drop by drop and the change was observed. The observations were recorded. The second part was oxidation, the procedure is the same as the procedure in bromination but this time instead of bromine in CCl4 we added 1.0 M solution of potassium permanganate. The change was observed and recorded. The last part for the reactions of hydrocarbons was sulphuric acid test; with the same procedure we added 0.50 ml concentrated sulphuric acid. The changes was observed and recorded. FIGURE 3: PREPARATION OF ACETYLENE

The last part of the experiment was the preparation and properties of Acetylene. For the preparation, as shown in figure 3, 2 g of calcium carbide was place inside an 8-in test tube. The test tube was clamped in an iron stand. 10 ml of distilled water was poured into the tube then a cork with rubber tubing was used to stop up the test tube. The rubber was extending into the water trough containing water and 5 micro test tube submerged in water. The acetylene gas was collected by the instructor using the downward water displacement method. For the properties, Ammoniacal silver nitrate test was first performed. 1 ml of freshly prepared ammoniacal silver nitrate was carefully transferred in the test tube containing acetylene gas. The reaction was observed and recorded. The second test was bromination, with the same procedure we added 1.0 bromine in CCl4 solution in the test tube containing the acetylene gas. The reaction was observed and recorded. The last test was oxidation, this time KMnO4 was added to the test tube containing acetylene gas. The reaction was observed and recorded. DISCUSSIONS AND RESULTS

Table 1: Physical Properties of Alkane, Alkene, and Aromatic Hydrocarbons.

COMPOUNDOBSERVATIONS

CyclohexaneCyclohexeneBenzene

FlammabilityYellow flame, no soot

Yellow flame, with sootYellow flame, more soot

SolubilityImmiscible ImmiscibleImmiscible

Flammability test can distinguish saturated and saturated compounds, alkene and aromatic compounds like cyclohexene and benzene have both produce sooth since alkene and aromatic are unsaturated compounds since they carbon-carbon multiple bonds. Therefore, compounds that produce soot or smoke are unsaturated compounds while does do not or produce small amount of soot are saturated compounds. Flammability can be used to distinguish alkene and aromatic compounds since they both produce sooth but in different amount. Hydrocarbons are not soluble with water because they are non-polar substrate and are not capable to form hydrogen bonds with water due to lack of hydrogen atoms connected to oxygen, nitrogen or fluorine. They also lack electronegative compound.Table 2: Reactions of Alkane, Alkene and Aromatic Hydrocarbons.COMPOUNDSOBSERVATIONS

CyclohexaneCyclohexeneBenzene

BrominationNo reactionLighterNo reaction

OxidationNo reactionWith brown precipitate decolourizationNo reaction

Reaction with conc. H2SO4No reactionWith reactionNo reaction

Bromination is done by alkenes when heated or in a presence of light via a mechanism know as free-radical substitution. Aromatic hydrocarbons which are unsaturated do not undergo addition reactions that will result it stability or no reaction will occur.

Table 3: Properties of AcetyleneREACTIONSOBSERVATIONS

Ammoniacal Silver NitrateFrom colourless it turns to dirty white.

BrominationThere was a smoke and its colour turned into dark orange.

OxidationAddition of KMnO4 turns it into colour brown.

The alkynes are the third homologous series of organic compounds of hydrogen and carbon, where there is at least one triple-bond between the atoms in the molecules. Acetylene is a linear molecule, all four atoms lying along a straight line. This linear structure can only be explained by the existence of sp hybridisation of the orbitals of the carbon atoms of ethyne. Acetylene is oxidised by a dilute aqueous solution of potassium permanganate to form oxalic acid. Thus, if acetylene is bubbled through a solution of potassium permanganate the solution is decolourised. This is Baeyer's test for unsaturated organic compounds.CONCLUSION

The objectives of this experiment are to differentiate alkanes, alkenes, alkynes and aromatic hydrocarbons through their properties, to visualize the characteristic reactions of alkanes, alkenes, alkynes and aromatic hydrocarbons, and to prepare acetylene gas. These objectives were achieved during the experiment since we are able to differentiate alkanes, alkenes and aromatic compounds using their physical properties. We also visualize the reactions of hydrocarbons. Lastly, we are able to prepare and test the properties of acetylene gas. I learned that unsaturated compounds are compounds that have carbon-carbon multiple bonds and produce soot when ignited. Also, hydrocarbons are insoluble in water since they are nonpolar compounds and they cannot form hydrogen bonds. Acetylene is a linear molecule, all four atoms lying along a straight line. This linear structure can only be explained by the existence of sp hybridisation of the orbitals of the carbon atoms of ethyne. Therefore, acetylene is an alkyne. I have learned many things about the properties, reactions and relationships about hydrocarbons. These concepts can be helpful in the future for us chemical engineering students.REFERENCES

Baluyot, J. Y., & De Castro, K. A. (n.d.). Organic Chemistry Laboratory Manual for Chemical Engineering Students.

Klein, D. (2012). Organic Chemsitry. Massachusetts: John Wiley & Sons, Inc.

Yaws, C. L. (2005). Yaws' Handbook of Physical Properties for Hydrocarbons and Chemicals. Knovel.

Experiment 06 Group No. 5 3/19/2015

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