Learning Objective: Extraction is used to separate a desired chemical compound from a mixture of compounds. In this procedure you will learn how to use the equipment involved in extraction.

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Students may wish to wear gloves when working with chemicals.

Students make all their own solutions in this lab class. You may prepare solutions individually, in partners or as a group. For this experiment, each experimenter needs 0.5 grams of benzoic acid combined with 0.5 grams of 1,4-dimethoxybenzene, 20 mL of tert-butylmethyl ether, 10 mL of 2M sodium hydroxide solution, 20 mL of a saturated sodium chloride solution and 20 mL of distilled water. When your solutions are prepared, you are ready to begin the separation procedure.

The following equipment is needed for the extraction setup: a ring clamp, a ring stand, a gravity funnel, a 125 mL separatory funnel with a Teflon stopcock and glass stopper, a spatula, and four Erlenmeyer flasks with corks to hold the separated solutions.

   
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Transfer the benzoic acid and 1,4-dimethoxybenzene mixture to an Erlenmeyer flask that contains 20 mL of tert-butylmethyl ether. Swirl and stir until dissolved (no solid particles). To minimize the time required for dissolving a solid, crush the solid beforehand so that maximum surface area is exposed. You can use a mortar and pestle or the bottom of a small beaker as your tool for crushing and grinding. Once solvent is added, stir vigorously. If the solute (the solid material you are trying to dissolve in the solvent) stubbornly refuses to dissolve, you can heat it gently.

   
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To set up for extraction, begin by attaching the ring clamp securely to the ring stand. Tighten or loosen the nut on the stopcock of the separatory funnel as needed and then place the separatory funnel in the ring clamp. Adjust the height so that an Erlenmeyer flask will fit underneath and make sure the stopcock is in the closed (horizontal) position. Be sure to pour all liquids at eye level. Transfer the solution prepared in Step 1 to the separatory funnel using a gravity funnel.

   
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Add about 20 mL of distilled water and note the development of two layers, an aqueous layer (bottom) and an ether layer (top). The ether layer contains both the benzoic acid and 1,4-dimethoxybenzene. Benzoic acid has a carboxylic acid functional group, which makes it an acidic compound, while 1,4-dimethoxybenzene has two ether groups and is neutral. Benzoic acid will react with a base like sodium hydroxide to create sodium benzoate, which is soluble in water.

   
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Add 10 mL of the 2-M sodium hydroxide solution (base) to the separatory funnel and add the stopper. Remove the separatory funnel from the ring clamp and grip it firmly. Hold the stopper in place. Invert the funnel, gently swirl the mixture and then immediately vent by turning the stopcock to the open position to release built-up pressure. Notice that you need to hold the stopper in place with one hand while turning the stopcock with the other.

When you vent, the tip of the separatory funnel should not point at YOU, or ME, nor your nearest neighbor.

With the funnel inverted and the stopcock firmly in place, do this: shake, shake, shake, vent. Again: shake, shake, shake, vent. One more time! Mix the contents thoroughly and then return the separatory funnel to the ring clamp. Allow the layers to settle and separate. Open the stopcock and drain the lower layer (aqueous) into flask 1. Try to cleanly separate the upper and lower layers.

   
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Next add 20 mL of saturated sodium chloride solution to the separatory funnel to dry the ether layer and drive out any suspended water molecules. As in Step 4, shake, shake, shake, vent. One more time! Return the separatory funnel to the ring clamp and let the layers settle and separate. Remove the stopper and drain the lower aqueous layer containing the sodium chloride solution and water into flask 2. Set aside to be discarded. The organic layer is poured out through the top into flask 3.



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