Separating the Components of a Mixture

Transcription

1 Separating the Components of a Mixture Introduction Many naturally occurring substances occur as mixtures rather than pure substances. There are two main types of mixtures, homogeneous and heterogeneous. Homogeneous mixtures appear uniform throughout, the individual particles cannot be visually identified. Heterogeneous mixtures are not uniform throughout; the individual particles of the components can be visually identified. In this laboratory, a ternary (3 components) heterogeneous mixture will be separated and the components recovered using physical and chemical methods. Physical methods for separating the components of the mixture take advantage of the different physical properties of the components such as solubility and boiling point. For example, NaCl is soluble in water while SiO2 is not. Chemical methods of separation involve the selective reaction of one of the components in the mixture to form a new substance. Generally, after the components are separated a second chemical reaction is used to convert the new substance to its original form. Decantation: A process for separating the liquid component of a liquid/solid mixture. The solid is allowed to settle to the bottom of the container and the liquid carefully poured from the container (ideally without disturbing the solid component). The liquid portion is called the supernatant. Filtration: A process for separating a solid from a liquid. The liquid passes through a porous material such as filter paper but the pores are too small for the solid to pass through, and thus the solid remains on the filter paper. The solid is called the residue and the liquid is called the filtrate. Evaporation: A process in which heat is used to remove a solvent. The substance, called the residue, that remains after the solvent has been evaporated is the substance that was originally dissolved in the solvent. For more information: Chemistry: Atom s First by OpenStax sections Phases and Classification of Matter and 1.3 Physical and Chemical Properties Equations to use for the calculations: mass of NaCl recovered = mass of NaCl in 250 ml beaker - mass of empty 250 ml beaker mass of SiO2 recovered = mass of SiO2 on filter paper #1 mass of filter paper #1 mass of CaCO3 recovered = mass of CaCO3 on filter paper #2 mass of filter paper #2 percent of a component in the mixture = mass of component recovered mass of original sample x 100% percent recovery = total mass of recovered components mass of original sample x 100% percent error = mass of ( orginal sample ) ( total mass of recovered components ) x 100% mass of original sample GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 1 of 10

2 Materials: mixture containing NaCl, SiO2, and CaCO3 3M HCl 1M Na2CO3 250 ml beaker 125 ml Erlenmeyer flask ml beakers stir rod spatula funnel wire gauze beaker tongs 2 watch glasses 2 pieces of filter paper 10 ml graduated cylinder 50 ml graduated cylinder DI water bottle hotplates calculator Oven Procedure Note: This is an individual lab. You will be working on your own. 1. Obtain an unknown mixture and record the unknown number on the lab report sheet. Then weigh the unknown mixture in a tared 150 ml beaker and record the exact mass on your report sheet. 2. Add 30 ml of deionized water to the mixture in the 150 ml beaker, while stirring continuously. Continue to stir for an additional 2 minutes. Record your observations on the data sheet. 3. Determine the mass of a clean dry 250 ml beaker. Record the mass on the data sheet. Also determine the mass of a piece of filter paper and record its mass on the data sheet as filter paper #1. 4. Prepare the gravity filtration apparatus by placing a funnel in the massed 250 ml beaker. Fold the piece of massed filter paper and place in the funnel. Moisten the filter paper with deionized water from the wash bottle. See Separating a liquid from a solid techniques on the GCC lab website. 5. Slowly pour the unknown mixture into the funnel. Make sure the mixture does not get underneath the filter paper. It is best to pour a small amount of the mixture into the funnel at a time, waiting for it to filter some before adding more. A small amount of water should be used to rinse any remaining mixture from the beaker into the funnel. Record your observations on the report sheet. 6. Place the funnel containing the residue in a clean dry 150 ml beaker and place the 250 ml beaker containing the filtrate on a hot plate with a heat setting of 6 (230ºC). Cover the 250 ml beaker with wire gauze and record start time in the observations section and carefully evaporate the water from the filtrate. Be sure not to splash out any of the liquid. Go on to step #8 while waiting for the liquid to evaporate, but remember to check on the evaporation often. 7. After the water has been completely evaporated, turn off the hotplate, report the end time in the observation section, and let the flask cool for minutes. Determine the mass of the cooled flask containing the residue (evaporated filtrate). Record the exact mass and observations on the report sheet. (What is the identity of the residue left in the flask?) GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 2 of 10

3 8. Carefully pour 8 ml of 3M HCl in small increments onto the residue on the filter paper (from step #6). Rinse the remaining residue with a small amount of deionized water. Record your observations on the report sheet. 9. Carefully unfold the filter paper containing the remaining solid and place on a watch glass. Dry the solid and filter paper by placing the watch glass in the oven. Make sure you label a paper towel with your name and place it under your watch glass in the oven. Record the start time in the observations section of your report sheet. Go on to step #11 while waiting for the solid and filter paper to dry, but remember to check it often. 10. Once the solid and paper is dry, record the stop time and allow it to cool and determine its mass. Record its mass on the report sheet. (What is the identity of this solid?). 11. Add 15 ml of 1M Na2CO3 to the filtrate from step #8. Stir the mixture for a few minutes. Record your observations on the data sheet. 12. Determine the mass of a new piece of filter paper and record its mass on the data sheet as filter paper #2. Prepare the gravity filtration apparatus by placing a clean funnel in a 125 ml Erlenmeyer flask. 13. Slowly pour the mixture into the funnel. Make sure the mixture does not get underneath the filter paper. It is best to pour a small amount of the mixture into the funnel at a time, waiting for it to filter some before adding more. A small amount of water should be used to rinse any remaining mixture from the beaker into the funnel. 14. Carefully unfold the filter paper containing the solid and place on a watch glass. Dry the solid and filter paper by placing the watch glass in the oven. Make sure you label a paper towel with your name and place it under your watch glass in the oven (caution: oven will be very hot! Use beaker tongs if necessary). Record the start time in the observations section of this lab report. The filtrate can be discarded down the drain. Once the solid and paper is dry, record the stop time and allow it to cool and determine its mass. Record its mass on the data sheet. (What is the identity of this solid?). Please refer to the Laboratory Techniques Document on the CHM151LL Course Website for more detailed techniques and images of lab equipment. Clean-Up: Place filter paper in designated bins in the hood. Rinse everything well with soapy tap water followed by a quick DI water rinse. Clean your benchtop. Put all equipment back exactly where you found it. GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 3 of 10

4 Name: Separating the Components of a Mixture Pre-lab assignment Date: Purpose: Summary of procedure: Drawing of apparatus used: Instructor signature: Pre-lab points: GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 4 of 10

5 Page Intentionally Left Blank for Double-Sided Printing GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 5 of 10

6 Name: Data: Data Table: Unknown Number mass of unknown mixture mass of dry 250 ml beaker Separating the Components of a Mixture Lab Report mass of 250 ml beaker with NaCl mass of filter paper #1 mass of filter paper #1 with SiO2 mass of filter paper #2 mass of filter paper #2 with CaCO3 Observations: Step 2: Step 10: Step 4: Step 11: Step 6: Step 13: Step 8: Step 14: Step 9: Additional Observations: GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 6 of 10

7 Calculations: (mass of each recovered component, percent of each component in mixture, percent recovery, percent error) Results: Results Table: mass of NaCl recovered mass of SiO2 recovered mass of CaCO3 recovered total mass of recovered NaCl, SiO2, and CaCO3 percent NaCl in mixture percent SiO2 in mixture percent CaCO3 in mixture percent recovery percent error GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 7 of 10

8 Discussion Questions: 1. Describe possible places of error that may cause the following: a. (2 pts) obtaining a significantly larger amount of NaCl than was present in the original sample b. (2 pts) obtaining a significantly smaller amount of SiO2 than was present in the original sample 2. Use the information in the table below to answer the following questions soluble in: cold water hot water 3 M HCl 3 M NaOH benzoic acid no yes no yes Mg(OH)2 no no yes no Na2SO4 yes yes yes yes Zn(OH)2 no no yes yes a. (2 pts) Could you separate the components of a mixture of Mg(OH)2 and Zn(OH)2 by using only 3 M HCl? Yes or NO? Why or why not? Explain your answer. b. (3 pts) Briefly describe the procedural steps (step1, step 2, etc.) you would take to separate the components of a mixture of benzoic acid and Na2SO4 and recover the two separated substances. GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 8 of 10

9 3. Explain whether the following parts of the mixture separation involved a physical or a chemical change. a. (4 pts) Specifically in step 2, adding deionized water to the mixture and stirring to dissolve the NaCl, is this a physical change or a chemical change and how do you know this? b. (4 pts) Specifically adding HCl to the residue in step number 8, is this a physical change or a chemical change and how do you know this? What were your observations before and after adding the HCl to help you confirm your choice? c. (4 pts) Specifically adding Na2CO3 to the filtrate in step number 11, is this a physical change or a chemical change and how do you know this? What were your observations before and after adding the Na2CO3 to the filtrate to help you confirm your choice? 4. (2 pts) Discuss two sources of error and how they can be corrected in the future (2 pts) Now that you have completed the experiment please write a revised Purpose statement that more accurately reflects the function of this lab. GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 9 of 10

10 Conclusion: (5 pts) Summarize the results of the mixture separation. Use your data values to support. GCC CHM 151LL: Separation of a Mixture GCC, 2018 page 10 of 10