Abstract
Two experiments were conducted to explore the solubility and reactivity of hydrocarbons. In the first experiment, an alkane was added to multiple solvents to determine solubility before and after heat was added. In the second, bromine solution was added to several alkenes to determine responses. The first experiment confirmed that polar solvents (water, methanol) did not dissolve an alkane, even with heat applied. The second experiment did not confirm the expected change of color of the bromine solution in the presence of an alkene, possibly because too little or too weak bromine solution was used.
Introduction
The purpose of this laboratory experiment is to explore the solubility and reactivity of hydrocarbons. Hydrocarbons can exist in several forms, including saturated, in which only single C – C bonds exist, or unsaturated, in which there is at least one C = C double or C≡C triple bonds exist (Clark 2003). In addition, hydrocarbons can exist in acyclic forms, basically long strings of atoms with or without branches to the side, or in cyclic form in which the carbon atoms form one or more rings (Clark). These different molecular structures contribute to different solubility properties. It is these properties that will be explored in this experiment.
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The first experiment tests the ability of a variety of solvents to dissolve an alkane. According to Spurlock (2014), a nonpolar alkane should not easily dissolve in polar structures like water or methanol. The second experiment observes the response of an alkene to the presence of a halogen solution (bromine, in this case). Clark (2003) asserts that bromine solutions should change color in the presence of an alkene and that this is a test of the presence of an alkene. This laboratory will test both those assertions.
Results
The results of this experiment are noted in two tables, one recording the results from the addition of an alkene to each of six solvents (Table 1); and the second recording observations of adding bromine solution, drop by drop, to alkenes (Table 2).
Table 1. Results of Adding Alkanes to Solvents
| Solvent | Results Before Heat Applied | Results After Heat Applied |
| water | Did not dissolve; crystallized | Did not dissolve; same as before heat |
| Methanol | Did not dissolve; oversaturated | Did not dissolve; boiled without dissolving |
| n-butanol | Dissolved; oversaturated | Dissolved; completely |
| Ethylene glycol | Dissolved; mixed or partial results | Dissolved; slightly greater results |
| Toluene | Dissolved; almost completely | Dissolved; completely |
| Dichloromethane | Dissolved completely | Dissolved; no change from pre-heat |
Notes on results from Table 1: In the methanol case before heat was applied, the alkane changed from two scoops to about one scoop. This was interpreted as being oversaturated. In addition, a potential source of error arose from using the same stir-stick for all six vials after the heat was applied to the vials. This potentially introduced contamination across the vials.
In the second part of this experiment, adding the bromine solution to the three alkenes produced no response in any of them.
Discussion
In the first part of this experiment, an alkane was added to a variety of solvents to see if it would dissolve, and if solubility changed with the addition of mild heat. Alkanes are saturated acyclic hydrocarbons, consisting only of hydrogen and carbon atoms linked with single bonds. Spurlock (2014) notes that solubility of hydrocarbon is determined by “Like dissolve like.” Based on this, an alkane should readily dissolve another alkane-like structured product, but not dissolve a hydrocarbon that was not similar in structure. For example, because water has a polar structure (an H and an OH group) it is not “like” the nonpolar alkane added. Methanol (an alcohol) similarly has a polar structure. The alkane did not dissolve in water or methanol, even when heat was added. The other solvents do not have a polar structure and thus were able to dissolve the alkane added.
Table 2. Results of Adding Bromine Solution to Alkenes
| Alkene | Results Before Heat Applied |
| b-pinene | No response; nothing happened |
| toluene | No response; nothing happened |
| trans-stilbene | No response; nothing happened |
In the second experiment, bromine solution was added to three different alkenes. Alkenes are unsaturated hydrocarbons with at least one C=C double bond. Adding a halogen such as bromine to an alkene should result in a change of color of the bromine; this is a test for the presence of alkenes (Clark, 2003). In this experiment, however, either the amount or concentration of bromine used was too low to detect a color change.
Experimental Methods
The procedure used in this experiment comes from the course laboratory manual (Stranz, 2008, pp. 1-2). The experimental method consisted first of placing 1 mL of nine solvents in separate sample vials. The solvents used included: water, methanol, n-butanol, ethylene glycol, acetone, hexane, toluene, ethyl acetate, and dichloromethane. The instructions for the procedure were to include all nine solvents in vials; however, acetone, hexane, and ethyl acetate were omitted from this experiment per teacher instructions, leaving six remaining solvents as part of this laboratory. To each of the vials, approximately 0.5 mL of an alkane was added, swirled, and then observed to see if it dissolved in the solvent in that vial. Mild heat in the form of warm air from a hair dryer was used to assist after initial observations of solubility were made.
In a second step, 1 mL of dichloromethane was placed in each of five sample vials. To these was added 5 drops (or about a 5 mm. mound) of one of the following, each added in separate vials: cyclohexene, toluene, -pinene, camphene, and trans-stilbene. As with the first stage of this laboratory, two alkenes were omitted, cyclohexene and camphene, leaving only the remaining three on which the experiment was conducted. Again, the vials were swirled or stirred until fully dissolved. To each vial was then added drops of bromine solution, prepared with 1 mL of bromine combined with 99 mL of dichloromethane to form approximately a 2% solution of bromine. The bromine solution was added under a fume hood and using gloves. Responses of the solutions to the bromine addition were noted in the results section of this report.
- Clark, J. “The Halogenation of Alkenes.” Chemguide.co.uk. 2003. Web. Available from: http://www.chemguide.co.uk/organicprops/alkenes/halogenation.html
- Spurlock, D. “Solubility and Reactivity of Alkanes, Alkenes, and Aromatic Compounds Course Notes.” Indiana University Southeast. 2014. Web. Available from: http://homepages.ius.edu/DSPURLOC/c122/sol.htm
- Stranz, M. Organic Chemistry. Mason, OH: Cengage Learning, 2008. Print.
