Exploring Polar and Nonpolar Molecules Maddie Keisler Thursday Lab 12:30 pm November 13, 2013 Keisler 2 Introduction The objective of this lab experiment was to gain a better understanding of polar and non-­‐polar molecules with hands on experience. The polarity of the molecules is determined based on the shape of the molecule and also the bonding pattern in the molecule. Electronegativity is the measured attractiveness of an atom for electrons in a covalent bond. The more full a valence shell is the higher the electronegativity it has. The lower electronegativity the greater desire the atom has to lose or gain electrons. The electronegativity plays a huge role when determining the polarity of the entire molecule or compound. Different electronegativity’s normally lead to having different polarities in the molecule. When all of the bonds are balanced around the central atom, the molecule is polar, and when there are unbalanced bonds around the central atom the molecule is non-­‐polar. Molecules that are polar tend to attract with other polar molecules, and same with non-­‐polar molecules. Part 1 of this experiment was to test the solubility of metals in a nonpolar organic solvent. This experiment allowed us to extract metal ions within an aqueous solution. Part 2 of the experiment showed the different interaction and intermolecular forces between water, gasoline, ethanol, and 1-­‐butanol. This experiment showed us the different interactions that can occur when higher attractiveness of bonds is added to a solution. Part 3 of this experiment showed us that interaction of is emulsifier. The emulsifier created dispersion, which allows non-­‐polar and polar molecular to interact and dissolve with one another. Part 4 of Keisler 3 this experiment showed the difference of hydrophobic and hydrophilic surfaces. The water creates different forces for each of the surfaces, cohesive are stronger when on hydrophilic surfaces and adhesive are stronger when on hydrophobic surfaces. Experimental Procedure Dithizone Extraction of Metal 2 mL of Copper II Sulfate was obtained and placed into a test tube 2 mL of tolune was also added to the same test tube. The tube was corked and shook, 3 drops of dithizone was also added to the test tube, the cork was replaced and it was shook again. The observations were written down in a lab notebook. Phase Separations of Ethanol-­‐Gasoline Fuels 3 test tubes were obtained they were washed and dried before performing this part of the experiment. 1 mL of Ethanol and 5 mL of gasoline was added to the first test tube. 1 mL of 1-­‐butanol and 5 mL of gasoline was added to the second test tube. 5 mL of gasoline was added to the third test tube. All three test tubes were corked and shook. 3 drops of blue water was added to each test tube and the all the corks were replaced and the tubes were shook again. All of the observations in each tube were written down in a lab notebook. Emulsion Another test tube was obtained; 1 mL of vegetable oil and 1 mL of DI water was added into the test tube, it was corked and shook. Once it was shook, 2 drops of egg yoke was added to the test tube, and the cork was replaced and the tube was shook again. Keisler 4 Hydrophobic Surfaces and Surface Tension Pieces of prepared glass was obtain, one was coated with Rain-­‐X and the other one was just a bare piece of glass, a few drops was water was dropped on top of each piece and the observations were collected. Results Dithizone Extraction of Metal When the copper II sulfate was mixed with tolune and shook the first they did not mix. Two different layers were formed; the bottom layer was a blue color. After 3 drops of the dithizone and shaken again, the dithizone mixed with the copper, top layer, but did not mix with the copper II sulfate. The top layer changed to a plum/purple color and the bottom layer was still blue. Phase Separation of Ethanol-­‐ Gasoline Fuels When the Ethanol and gasoline were mixed together, before the water was added the two mixed together. After the water was added the ethanol dissolved better in the water and moved to the bottom of the test tube, and the gasoline was the top layer. When the 1-­‐butanol and the gasoline were mixed together they dissolved with one another. Once the water was added the water went to the bottom of the test tube and the other two stayed mixed together. The test tube with only gasoline with water added to it, the color changed slightly. Making the gas a partly cloudy and the gasoline did not dissolve with the water. They formed two separate layers, with water at the bottom. Keisler 5 Emulsion When the test tube only contained water and vegetable oil there were two different layers, water was on the bottom and oil was the top layer. Once the few drops of egg yoke was added and the test tube was shaken, everything mixed together. No layers in the test tube. The content in the test tube became a cloudy white color. Hydrophobic Surfaces and Surface tension When the water was placed on the bare glass, the drops spread out on the glass, flattening in a way. When the water was placed on the piece of glass that was covered with Rain –X the water got smaller and sat on top of the glass, forming water beads on the glass. ____________________________ ________________________________ Bare Glass Rain-­‐X coated glass Discussion The copper-­‐ dithizone complex was created because copper II is very soluble in organic substances. Copper II is polar molecule, water is a polar molecule, toluene is non-­‐polar molecule, dithizone is non-­‐polar as well, and the copper-­‐ dithizone complex is a non-­‐polar compound. When toluene was added to the dithizone it mixed together and the compound is a mostly nonpolar compound. Water does not dissolve in gasoline. Ethanol alone dissolves in gasoline, but ethanol prefers water over gasoline, so when water was also added to test tube, the ethanol separated from the gasoline and dissolved in the water. Ethanol and water Keisler 6 have greater intermolecular forces because formed hydrogen bonds, where as gasoline and ethanol formed a non-­‐polar non-­‐polar intermolecular forces. Forces can be easily broken when a molecule can form a stronger intermolecular force with another molecule. In this case the ethanol changed from bonding with gasoline to water. 1-­‐ butanol and gasoline dissolve together because that was the greater force in the test tube even when the water was added. Gasoline does not dissolve in water, so that did not play a factor when the water was added; 1-­‐butanol favors gasoline over water when they are all together. They can form a stronger intermolecular force then the 1-­‐butanol and water can. When water was added to the test tube that contained only gasoline, they formed to separate layers, they did not dissolve together, gasoline is a hydrophobic molecular. Meaning that it does not like water therefore it will not dissolve in water. Emulsifier is when it allows two molecules that do not normally dissolve in one another to dissolve with each other. This happens because the emulsifier creates dispersion between the two molecules, which will allow them to dissolve with one another. The oil and water did not dissolve in one another until the egg yoke was added. With the addition of the egg yoke the substances gladly mixed together, because of this result we can conclude that egg yoke is indeed an emulsifier. The egg yoke created dispersion between the two. Surface tension is the amount of measurable energy that is needed to increase the surface area of a liquid by a unit of area (Purdue). The surface tension of a liquid produces an imbalance of intermolecular attractive forces. Cohesive forces are stronger when water is on a hydrophilic surface, such as the bare piece of Keisler 7 glass. The adhesive forces are stronger then the cohesive forces, which allows the water to spread out over the glass. When water interacts the hydrophobic surfaces, in this case a piece of glass that was covered with Rain-­‐X, the cohesive forces are stronger than the adhesive forces. When the cohesive forces are stronger the water gets a small as possible, trying to get away because it’s interacting with a hydrophobic surface. Conclusion Copper II is very soluble in organic solvent, dithizone is an organic solvent, when it was added the copper II dissolved in it, and where as when it was mixed with the toluene they separated and formed two different layers. Water does induce the separation of ethanol and gasoline, because water and ethanol create stronger bonds. However water does not induce the separation of 1-­‐
butanol and gasoline. The bonds between 1-­‐butanol and gasoline are strong enough that water cannot break them, and bond with 1-­‐butanol. Egg yoke does have an emulsifier in it, when the egg yoke was add to oil and water in allowed them to dissolve in one another, because the egg yoke created a dispersion. A Rain-­‐X treated surface is hydrophobic; it makes the water or any other hydrophilic liquid to form small beads of liquid. Making the small as possible, because of the adhesive forces are stronger the cohesive forces when on a hydrophobic surface. Literature Cited Surface Tension. Chem. Purdue. 13, November 2013 http://www.chem.purdue.edu/gchelp/liquids/tension.html Keisler 8