Chemistry Materials Separation Processes

Transcription

1 Chemistry Materials Separation Processes You will be assigned to separate a mixture of several different materials. However, first you will need to learn about several techniques used for mixture separation. More specifically you will study and describe techniques involving magnetic attraction, settling and decanting, filtration, vacuum filtration, evaporation, and distillation. Read through the following paragraphs of procedures and then write a summary of each technique in your own words. Magnetic attraction: Magnetic separation is a relative easy process. It is used to separate particles out based on magnetic properties. You need a magnet and a plastic bag. Place the magnet in the plastic bag. Run the plastic covered magnet through your mixture collecting whatever will stick to it. Place the magnet/bag over an empty bag and remove any particles sticking to the magnet by simply pulling the bag off the magnet. Repeat this process until no more particles stick to the magnet. Settling and decanting: This process is used for a solid suspended in water, which is allowed to settle to the bottom of a container under the influence of gravity. Pouring it away into another container then separates the water. Allow the beaker to sit until the bottom is covered with solid particles and the liquid is clear. Grasp the beaker with one hand. With the other hand, pick up a stirring rod and hold it along the lip of the beaker. Tilt the beaker slightly so that liquid begins to pour out in a slow, steady stream. Keep pouring until all of the liquid is poured out of the initial beaker. It should be obvious that you need to be as careful as possible not to transfer any of the solid to the second beaker. 1

2 Sifting or sieving: Is a form of filtration used to remove larger particles from smaller ones. For this process you will need a screen with holes big enough to let smaller particles pass through yet small enough that larger particles remain trapped on the screen. This is most effective if the material to be sieved is dry. Gravity Filtration: Prepare a piece of filter paper by folding it in half and then in half again. Open the folded paper to form a cone. The cone is then placed into a funnel Next, put the funnel, stem first, into a beaker suspended from an iron ring attached to a ring stand. Wet the filter paper with a little water so the paper will stick to the sides of the funnel. Pour the mixture to be filtered down a stirring rod into the filter in the funnel. Do not let the level of the mixture in the funnel rise above the edge of the filter paper. You can use this as part of the decanting process described above to catch particles that may have escaped during decantation. You should measure the mass of the filter paper before you put it in the funnel and again after it has completely dried. This will give you the mass of any solid trapped by the filter paper. 2

3 Vacuum Filtration: This process is used when gravity filtration may take a very long time. The set up is more complicated than gravity filtration, but may save you some time if you have a lot of sediment or precipitate to filter. You need the following pieces of equipment: aspirator, rubber tubing, Buchner funnel, ring, ring stand, Erlenmeyer filter flask, filter paper, and wash bottle. Attach the aspirator to the faucet. Turn on the water. Water should run without overflowing the sink or spitting water while making a vacuum. To test for a vacuum, cover the opening of the horizontal arm of the aspirator with your finger or thumb. If you feel your thumb being pulled inward, there is a vacuum. Note the number of turns of the knob that are needed to produce the flow of water that create a vacuum. Turn the water off. Attach the rubber tubing to the horizontal arm of the aspirator. Water should not run down this tube. Attach the free end of the rubber tubing to the side arm of the filter flask and check for vacuum when the water is turned on. Place the palm of your hand over the mouth of the Erlenmeyer flask. You should feel the vacuum 3

4 pull on your hand. Increase the flow of water if needed. Insert the neck of the Buchner funnel into a one holed rubber stopper until the stopper is about two-thirds to three-fourths up the neck of the funnel. Place the funnel stem into the Erlenmeyer flask so that the stopper rests in the mouth of the flask. Obtain a piece of filter paper. Place it inside the Buchner funnel over the holes. Turn on the water as before. Hold the filter flask with one hand place the palm of your hand over the mouth the funnel to check for vacuum. Pour the mixture to be filtered into the funnel. Use a wash bottle to rinse all the mixture form the beaker into the funnel. Distillation: Used to separate materials with different boiling points. You will need the following equipment: Beaker (1 or more, depending on the number of components in the mixture), Liebig Condenser (1),Thermometer, (1)Distilling Flask, Utility Clamps (2, minimum), Ring stand (2), Rubber tubing (2, 16"-24" length each), Bunsen burner and tubing (1), Rubber stopper or cork, one-hole (2). Attach a utility clamp to each ring stand. Carefully insert the flask sidearm into a one-hole stopper or cork. Use a twisting motion with gentle pressure. Protect your hands with paper towels, and use water or glycerin to lubricate the sidearm. 1 cm or less of the sidearm should stick out of the stopper when finished. Attach the distilling flask to one of the mounted utility clamps. Place the jaws of the clamp below the sidearm of the flask. Adjust the height of the clamp and flask to 4

5 leave enough room for the Bunsen burner. Carefully insert a thermometer into a one-hole stopper or cork. Use a twisting motion with gentle pressure. Protect your hands with paper towels, and use water or glycerin to lubricate the thermometer. Place the stopper in the opening of the flask's neck. Adjust the level of the thermometer so that the bulb is the same height as the flask sidearm. Attach the Liebig condenser to the second mounted utility clamp. The angle of the clamp will need to be adjusted so that it matches the angle the flask sidearm makes with the flask neck. Adjust the height of the condenser utility clamp and move the condenser ring stand so that the opening of the condenser column is even with the sidearm stopper. Insert the sidearm stopper into the opening of the condenser column and ensure that there is a snug fit. Attach one length of rubber tubing to the lower condenser jacket sidearm. The other end of the rubber tubing should be placed over the nozzle of the lab sink. Attach the second length of rubber tubing to the upper condenser jacket sidearm. The other end of the rubber tubing should be placed into the sink to allow the condenser water to drain. Place a beaker underneath the spout of the condenser to collect the distillate. Attach a Bunsen burner to a gas jet, and adjust the tubing so that the burner sits safely beneath the distilling flask. Evaporation: This process is used to separate water from a solid either by slowly heating the material or letting an open container sit for several days. For more rapid separation you may wish to slowly heat the mixture to evaporate any water remaining in a solid after it has been filtered or decanted. You may use a hot plate or ring stand 5

6 with a burner to accomplish this. To use a hot plate you simply put the beaker or dish containing the wet solid on a hot plate and adjust the heat to allow the water to be evaporated. Leave the container on the hot plate until all the water is evaporated. The same results may be accomplished using a burner. Set up a ring, ring stand, and wire mesh. Place a burner beneath the wire mesh. Light and adjust the burner. Place the container to be heated on the wire mesh. The flame should be adjusted so spattering of the solid material does not occur. If spattering will most likely occur, a watch glass (concave side up) may be placed on the heated beaker. Again heat the glassware until all water has been removed. This may take some time depending on the amount of water remaining in the solid. An alternate method is to simple put the beaker or flask on a shelf and let it stand for several days until all the water has evaporated. This process may not work well on days of high humidity. Assignment: Your assignment is to write a brief summary of each procedure in your own words. Write your summary on your own paper. 6