Experiment 3 – Methods of Evaporation and Filtration Used to Separate Mixtures I. Purpose Separate homogeneous mixtures using physical means, such as gravity filtration, vacuum filtration, etc. Purification of a compound by recrystaliization. II. Introduction Is bottled water safer than tap water? Studies have revealed that phthalates, chemicals known to affect hormones, can come from the plastic material of the bottled water. In addition, at least 25% of bottled water contains tap water inside. These studies suggest that consumers should become more aware of what they are drinking. Besides chemical contaminant concerns, the shipment and production of plastic bottled water has environmental consequences. Simply moving large amounts of bottled water from one location to another creates global warming and other types of air pollution. The production of plastic bottled water requires millions of barrels of crude oil each year that affects the environment as well. The environment is also impacted by the disposal of plastic bottles. Most of the bottles are either sent to landfills or left as unclaimed trash instead of being recycled. If bottled water is environmentally unfriendly, then drinking tap water may be a better alternative. However, consumers may be reluctant to trust the water coming out of their faucets unless there is scientific evidence that tap water is safe to drink. Companies like Brita® have already come up with faucet filtration systems to make tap water safer to drink. The separation of unwanted particulates from a mixture plays a major role in filtration systems. III. Materials Saturated NaCl solution 1 M Na2CO3 1 M CaCl2 6 M HCl Filter paper Vanillin Büchner funnel IV. Safety Precuations Be cautious with the acids and bases used in this experiment. Dispose all chemicals as instructed. V. Experimental Procedures Part 1. Separation of Mixtures by Evaporation 1. Weigh and record the mass of a clean and dry evaporating dish using an analytical balance. 2. Pour onto the evaporating dish approximately 5 mL of a saturated NaCl solution. 3. Reweigh and record the evaporating dish with the NaCl solution on it. 29 4. Set up a heating apparatus similar to the illustration below (Figure 3A). 5. Choose an appropriate size beaker that will hold the evaporating dish directly on top. 6. Add several (about 3 – 5) boiling chips into the beaker to avoid bumping. 7. Fill the beaker half full with tap water. Wire Gauze Iron Ring Figure 3A: A heating apparatus. 8. Place the evaporating dish with the saturated NaCl solution directly on top of beaker. 9. Turn on the flames from the Bunsen burner and heat until there is no apparent liquid on the evaporating dish. Turn off the flames. 10. Carefully remove the evaporating dish and the beaker from the heating apparatus. 11. Place the evaporating dish back on the wire gauze. 12. Apply a very gentle flame (approximately 2 minutes) underneath the wire gauze to completely evaporate any residues of liquid that may remain on the evaporating dish. 13. Allow the evaporating dish to cool and weigh the dish. Repeat the heating, cooling, and reweighing process until constant mass is reached. 14. Calculate the mass percent of NaCl in the saturated NaCl solution. 30 Part 2. Separation of Mixtures by Gravity Filtration 1. Add 10 mL of 1.0 M sodium carbonate into a 150 mL beaker. 2. Into the same beaker, add 10 mL of 1.0 M calcium chloride and stir the mixture with a glass stirring rod. 3. Write a balanced chemical equation for this mixture. 4. Set up a gravity filtration setup similar to the illustration below (Figure 3B). Make sure to wet the filter paper with deionized water to ensure that it sticks well to the funnel. 5. Using the glass stirring rod as a guide, pour the sodium carbonate and calcium chloride mixture directly into the center of the funnel. Make sure to point the glass stirring rod directly into the middle of the funnel without touching the filter paper. 6. Any solids will be retained by the filter paper while liquids will flow through due to gravity. The liquids will be collected underneath into a beaker. 7. When the filter paper appears dry, remove it from the funnel. 8. Open up the filter paper completely and transfer some solids to a watch glass. 9. Add 3 drops of 6 M HCl to the solids on the watch glass. 10.Write a balanced chemical reaction for the observed reaction. Funnel Iron Ring Figure 3B: A gravity filtration setup. 31 Part 3. Separation of Mixtures by Vacuum Filtration 1. Place a 250 mL Erlenmeyer flask on an analytical balance and press “Tare.” 2. Weigh and record the mass of 0.8 g to 1 g of vanillin into the 250 mL Erlenmeyer flask on the analytical balance. 3. Remove the Erlenmeyer flask from the balance and add approximately 50 mL of deionized water and vigorously stir to dissolve as much vanillin as possible. 4. Using the flames from a Bunsen burner, gently heat the solution in the flask until all the solids dissolve. Do not allow the solution to boil. Turn off the flames and allow the solution to cool for several minutes. 5. Put the Erlenmeyer flask into an ice bath. As the solution cools down in the ice bath, crystallization should occur. If there are no signs of crystals forming when the flask feels cold, insert a glass stirring rod into the flask and gently scrap at the bottom. 6. Once crystallization is complete, assemble a vacuum filtration setup similar to the illustration below (Figure 3C). Buchner Funnel Rubber Hose Utility Clamp Suction Flask Figure 3C: A vacuum filtration setup. 7. Obtain an appropriate size filter paper that fits well at the bottom of the Büchner funnel. Weigh the filter paper using an analytical balance. Place the filter paper at the bottom of the Büchner funnel and wet it with deionized water. 8. Turn on the water line where the rubber hose is attached, as this will create a suction effect. 9. Rinse the crystals in the Erlenmeyer flask with approximately 5 mL of ice-cold water and carefully pour the crystals into the center of the Büchner funnel. 32 10. If there are crystals still remaining in the Erlenmeyer flask, rinse them with an additional 5 mL of ice-cold water and pour them into the Büchner funnel. 11. When the crystals appear to be dry, turn off the water line to stop the suction and carefully remove the filter paper from the Büchner funnel. 12. Place the filter paper containing the crystals on watch glass and allow it to dry in the lab drawer. 13. In the next lab class, weigh and record the mass of the filter paper containing the vanillin. 14. Calculate the percent recovery of vanillin. VI. Questions 1. An evaporating dish weighs 44.3170 grams. After 8.5 mL of salt water was added to the dish, the combination of the dish and salt water weighed 52.987 grams. The dish was then heated until a constant mass of 44.5990 grams was obtained. What was the mass percent of salt dissolved in the salt water? 2. What is meant by “constant mass”? How is this important? VII. Discussion Questions 1. In the previous experiment, distillation was performed to purify water from tap water. In this experiment evaporation, gravity filtration, and vacuum filtration were methods used to separate homogeneous mixtures. Would it be safe to drink purified sewage water if these methods were used to separate water from unwanted substances? VIII. References 1. Bottled Water. Website accessed on November 14, 2010: http://www.nrdc.org/water/drinking/qbw.asp. 2. Brita Faucet Filtration. Website accessed on November 14, 2010: http://www.brita.com/products/faucet-filtration/. 3. Drinking Water: Bottled or From the Tap? Website accessed on November 14, 2010: http://kids.nationalgeographic.com/kids/stories/spacescience/water-bottlepollution/. 4. Murov, S., Experiments in General Chemistry, Separation of Mixtures, (2006) 5th Ed., Thomson Brooks/Cole 33 Lab Reports : 11 cover sheet 21 Title 37 Abstract 41 Introduction 51 Datal observations 61 sample calcanlation 71 Discussion procedure (then third person 8 81 Conclusion. Disscussion 9 conclusion 101 Post - Lab Raw data.
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