There is one more part of this process that would make it a complete recrystallization. Instead of filtering, can the solution be allowed to evaporate to leave the sodium oleate behind? After filtration, list the contents of the solution.ĥ. This solid can be filtered away from the water.Ĥ. If the resulting solution is cooled to room temperature, the sodium oleate is no longer soluble. It’s possible that, in the right amount of hot water, all the sodium oleate and all the sodium chloride dissolves. For example, the solubility of sodium chloride is different in cold water (35.7 g per 100 mL at 0 C) than in hot water (39.12 g per 100 mL at 100 C). It is found on the front of your hot plate in the organic lab. When the switch is off, the sodium oleate comes out of solution again so that you can filter it out. When the switch is on, all the sodium oleate dissolves, and any sodium chloride trapped inside can get dissolved, too. ![]() It would be convenient if there were a switch that could be turned on and off to control dissolution. How can you get all of the sodium chloride out of this mixture? In other words, how can you make sure there is no sodium chloride covered by sodium oleate? Washing might remove most of the exposed sodium chloride, but it wouldn’t touch the hidden or “occluded” sodium chloride that was surrounded by sodium oleate molecules.ģ. ![]() This situation is very common, especially when the two compounds have formed together. There might be a small nugget of sodium chloride surrounded by a coating of sodium oleate. Instead of having individual grains of sodium chloride and individual grains of sodium oleate, the grains of powder contain both compounds. Suppose there is a pile of powder that contains sodium oleate and sodium chloride. Sometimes in a mixture the two compounds are mixed very tightly together. Sometimes it can increase the purity of a compound, but it is not always very effective. The sodium oleate was washed with water to remove sodium chloride. The technique described above is not recrystallization. It could be gathered or “isolated” by filtration. Sodium oleate is less soluble in water than is sodium chloride, so most of it would not dissolve. If the right amount of water were added and the resulting slurry were stirred together and filtered, much of the sodium chloride would be removed because it is more soluble in water than is sodium oleate. It’s possible that a mixture of sodium chloride and sodium oleate could be purified through the addition of water. Can you qualitatively explain the difference between their solubilities in water? Look at the structures of sodium chloride and sodium oleate. Describe how you could get pure sodium oleate.Ģ. ![]() Maybe you find you can easily produce a mixture of equal parts (weight:weight) of sodium chloride and sodium oleate. Suppose you were trying to go into the soap business. That difference can be exploited to separate these two compounds.ġ. Sodium chloride (table salt) has a particular solubility in cold water (35.7 g will dissolve in 100 mL) while sodium oleate (found in some soaps) has a different solubility in cold water (10 g per 100 mL). Solubility in a solvent is a physical property of a material, just like its boiling point or melting point. If one compound is an undissolved solid, it can be filtered out of the solution in order to separate it from all the other things that are in solution. The goal of this method is to have one compound dissolved in a solvent while the other compound is not dissolved. Recrystallization depends on different solubilities of the target compound and other compounds present in the impure mixture. The mixture is slowly cooled again until a pure solid is obtained. The mixture that results is heated until the solids dissolve. The method involves addition of a cold solvent to the material. Usually this method works best when there is only a small amount of impurity in the solid. Recrystallization is used to purify solids.
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