Alkanes, Alkenes, Alkynes

Experiment #1

ALKANES, ALKENES AND ALKYNES

Ortiz, Darren, Samia, Geanne Samantha, Santos, Christian Mike

College of Science
University of the Philippines Baguio

Abstract

Alkanes, alkenes, and alkynes are organic compounds called hydrocarbons. This experiment was performed to determine the differences in the properties of alkanes, alkenes and alkynes through its representative compounds; butane, ethylene and acetylene. Butane gas was collected from a lighter while acetylene gas from the reaction of calcium carbide with water both through the process of water displacement. Ethylene on the other hand was collected from the heating of polyethylene in an aluminum foil. Butane and acetylene gases were subjected to combustibility test, and all three (butane, ethylene and acetylene) were reacted to bromine. The combustibility of butane yielded a blue flame and a transparent to whitish smoke (no soot); acetylene produced a reddish to orange flame and black smoke (with soot). Butane gas was reacted with bromine observed in two conditions; with the presence and absence of light. This generated a lighter color for the solution in the former and no change in color for the latter. The reactions of ethylene gas and acetylene gas with bromine turned the solution into a lighter color.

Introduction

Hydrocarbons, are compounds which contain the carbon and hydrogen atoms only. (Atkins et.al, 2013). It is divided into two main classes, namely the aliphatic hydrocarbons and aromatic hydrocarbons. Aliphatic hydrocarbons are further subdivided into three groups; the alkanes, alkenes, and alkynes. These three groups of aliphatic hydrocarbons are the focus of this experiment.

        Alkanes are hydrocarbons with single carbon bond. They are chemical compounds that play a major role in everyone’s life as they are found mostly in plastic products, natural gas, gasoline; and without alkanes, these important things can never be achieved by people (Garcia, 2016). One derivative of alkanes is butane. Butane has a chemical formula of C4H10. According to the Government of Western Australia Drug and Alcohol Office, butane is considered to be very flammable, colorless, and odorless. It can be found in products such as lighters and aerosol sprays and in liquefied petroleum gas (LPG).

        Alkenes (also known as olefins) on the other hand, are hydrocarbons which contain carbon-carbon double bond (Atkins et.al, 2013). The two simplest alkenes are ethene and propene - both also known as ethylene and propylene. Ethylene occurs naturally as a plant hormone but in very small amounts. It is also involved in the ripening of fruits and a major component of plastic polyethylene bags.

        The last classification of aliphatic hydrocarbons is the alkynes. Alkynes are the organic chemical compounds or hydrocarbons that have carbon-carbon triple bonds in their structure which is their distinguishing characteristic. Alkynes are generally in gaseous phase or form and they are easily dissolved in organic solvents such as benzene and acetone but are insoluble in water. One characteristic of an alkyne is that, when it is burned, the flame produces a sooty flame. Acetylene is one of the most common alkyne. It is considered to be useful and significant due to its capacity to undergo several chemical reactions needed manufacturing industrial products (Garcia, 2016).

        Chemical compounds with double and triple bonds in their chemical structure are considered to be unsaturated hydrocarbons. Meanwhile, chemical compounds with only single bond in their structure are said to be saturated hydrocarbons. Since alkanes have only single bond, they are referred to as saturated ones; and since alkenes and alkynes have double bonds and triple bonds respectively, they are called the unsaturated hydrocarbons (Garcia, 2016).

        This experiment covers the preparation and characterization of the three organic compounds. It aims to prepare the representative of each group especially butane, ethylene, and acetylene, to know the properties of the three representatives by performing different chemical tests and to distinguish saturated hydrocarbons from unsaturated hydrocarbons. Lastly, this experiment intends to write a chemical equation for the reaction of butane, ethylene, and acetylene. Along with these, it was conducted to determine the different properties of the three representatives of aliphatic hydrocarbons and to observe the reactions and changes when butane, ethylene, and acetylene are subjected to combustibility and test with bromine.

        The report can further be a reliable reference for students who are and about to conduct such experiment since this experiment was done in precise manner and with the proper guidance of a professor. This report can also be helpful for researchers who are doing studies regarding aliphatic hydrocarbons and their properties. Finally, this could be a great help for people who wanted to understand and know the applications of alkanes, alkenes, and alkynes hydrocarbons.

Results and Discussion

Table 1. Properties of Hydrocarbons

Table 1 presents the observations on the test compounds (butane, ethylene and acetylene) after testing its combustibility and reaction with bromine.

For the convenience and organization of discussing the results, it will be divided and will be discussed into two portions according to the tests administered; (a) Combustibility Test and (b) Reaction with Bromine