Separation of a Mixture of Salt and Sand

Transcription

1 CH104 General Chemistry Lab Name: Separation of a Mixture of Salt and Sand Learning Purposes: Give names and uses of common lab glassware. State metric units used for measurements of length, mass, and volume. Explain how to adjust flame color and flame height on a bunsen burner. Propose macro illustration for the principle behind filtration. Calculate and report the % composition of salt and sand in the mixture. You may work with a partner on the following lab activity. Mark each step as you complete it. Write down all observations and measurements. 1. Identify and assemble the following equipment on your bench: Beaker Erlenmeyer Flask From your drawer: a. 3 beakers: L, M, and S d. wire gauze b. 125mL erlenmeyer flask e. porcelain evaporating dish c. funnel f. 25mL graduated cylinder From the Lab Carts: a. bunsen burner and matches b. ring clamp c. approximately 50 ml of distilled water in a medium beaker d. approximately 10 ml of salt and sand mixture in a small beaker. e. filter paper 2. Take your beaker containing the salt and sand mixture, along with the small flask, and weigh out about 5 grams of the mixture on the centigram balance as follows: a. Place a piece of weighing paper on the balance pan. Close the top of the balance, if necessary. Wait until the reading holds steady and push the tare button. The balance should now read 0.00 grams. b. Open the top of the balance. Hold the mouth of the beaker containing the mixture of salt and sand over the weighing paper, then tap on the side of the beaker so that small amounts of the mixture pour onto the paper. Keep adding the mixture until you have a mass between 4.5 and 5.5 grams. c. Record the mass of your sample in grams, including all digits. g d. Pour the sample from the paper into the flask. e. Use a brush to sweep any spilled sample onto the weighing paper. f. Dispose of the paper in the trash can. 3. At your bench, use the graduated cylinder to measure exactly 25.0 ml of water. Read the volume from the bottom of the meniscus. ( Meniscus: the curve of the liquid surface.) Pour the water into the flask containing the mixture. Describe the appearance before, during, and after swirling the mixture continuously for 1 minute. mensicus----> 4. Filter the mixture as follows: a. Place the funnel in a ring clamp and set the clamp so that the end of the funnel feeds into a small beaker. See diagram on next page. -1-

2 b. Fold a piece of filter paper into quarters and place into the funnel, forming a cone. Wet the paper with a squirt from a wash bottle to hold the paper in place. c. Leaving as much solid on the bottom of the flask as possible, transfer the liquid into the funnel by pouring the liquid down a stirring rod. (see instructor demo) d. The liquid (called the filtrate) should come through the filter with a clear appearance. If necessary repeat the filtration step with new filter paper. Record description of the process. e. Use the 50 ml graduated cylinder to measure the total volume of the filtrate. Record the volume (to 0.1 ml). Initial volume ml 5. Evaporate the filtrate as follows: a. Weigh a porcelain evaporating dish and record the mass. g b. Pour 8-10 ml of filtrate into the evaporating dish. Record the remaining volume of filtrate in the graduated cylinder (to 0.1 ml). Final volume ml c. Adjust the a ring clamp so it rests 3-5 inches above the bunsen burner. Place a wire screen on the clamp, and set the evaporating dish on the wire screen. d. Connect the burner to the gas outlet, and have the instructor inspect your set-up before you light the burner. Instructor initials: e. Wear safety glasses. Watch your hair and clothing, and have proper footwear. f. Clear the work area around the burner. g. Light a match and hold it over the end of the burner. Open the bench valve completely (the valve handle should point at the end of the valve nozzle.) h. Adjust the flame color to blue by turning the barrel, and adjust the heightof the flame using the knob at the base of the burner so that it just touches the bottom of the gauze on the ring clamp. j. Allow the liquid to come to a boil in the evaporating dish and keep heating until the water completely evaporates. k. Turn off the burner by closing the bench valve in either direction until it stops. Record descriptions of events. 6. Microscope observations. Can be done at any point in the lab. Partners should observe together. Samples of pure salt and various sand mixture should be set up with a dissecting microscope. Examine the samples under the microscope and describe the appearance of the particles you see. Identify specific differences in size, color, shape, and texture between the salt crystals and the grains of sand in drawings and your description. Distinguish between the various types of sand in your descriptions. -2-

3 7. Final measurements. a. Allow the evaporating dish to cool enough so you cannot feel heat rising from it (usually about ten minutes). 8. Clean-up b. Use crucible tongs to grab the evaporating dish and take it to the weighing room. Support the evaporating dish on a notebook or on a beaker during transport. c. Tare the balance to zero and weigh the dish with the salt. g a. Rinse out the salt in the sink. c. When the ring clamp and gauze have cooled sufficiently, disassemble and return all equipment to the appropriate areas. d. Leftover dry mixture may be returned to the community area. Wet sand may be discarded into the trash. Rinse the flask, funnel and other glassware with water before returning them to your drawer. e. Wipe your bench with a wet paper towel. f. Return your key to the key board. g. Obtain instructor initials and you have completed the lab activity. Data Table is used to organize the observations and measurements made during the lab. 1. Mass of Salt/Sand sample Be sure to include units 2. Initial Volume of Filtrate 3. Final Volume of Filtrate 4. Mass of empty evaporating dish 5. Mass of evaporating dish + residue Initials Analysis. Show all work; include units throughout the calculations. Do Scratch work on separate paper. 1. Calculate the volume of filtrate heated in the evaporating dish to obtain the salt residue. 2. Calculate the mass of the salt residue. 3. Calculate the total mass of salt as follows: (Initial volume of filtrate) X (Mass of salt residue) = (Total mass of salt) (Volume of evaporated filtrate) 4. Calculate the percentage composition iof salt in the original sample as follows: (Total Mass of Salt) X 100% = Percent of Salt in the Mixture (Mass of Salt/Sand Mixture) -3-

4 Results Table. Used to display the information from the analysis. 1. Mass of the Sample Mixture 2. Volume of Evaporated Filtrate 3. Total Mass of Salt in the Sample 4. Percentage of Salt in the Sample Questions. (Due at the beginning of the next lab.) Underlined terms can be found in the text index. Use complete sentences and include appropriate definitions. 1. In this activity you start with a mixture of salt and sand. After filtration and evaporation the mixture is separated into two components. What is the physical property of salt that allows this method to work? 2. a. Is sand a pure substance? Explain on the basis of your observations. Include the definition. b. Is salt (NaCl) a pure substance? Explain. 3. Summarize the physical change in the appearance of the salt before dissolving, and after evaporation of the water. 4. The salt could be seen in the microscope as distinct from the sand. After dissolving in water, the salt reappears after boiling off the water. On the basis of these observations classify the dissolving of salt as either a physical change or a chemical change and explain your reasons. -4 -

5 5. Dry salt cannot pass through filter paper. Formulate an hypothesis explaining why it is possible for the water and the dissolved salt to do so, while the sand stays behind. Use a macro example to illustrate the micro process of filtration in your discussion. 6. Describe an example from daily life in which filtration is used to separate two or more substances. Summary and Conclusion Write a succinct summary of your work by including a paragraph for each point in the Learning Purposes found at the beginning of this handout. Each paragraph should begin with a sentence that addresses the learning point. This statement should be supported by specific examples from your work in the lab. -5-