CHEM 211-2007 2 Experiment 4 How and Why Do Substances Dissolve? Solutes Solvents G. General Overview of the Experiment: You will work in groups of three or four with a manager, a recorder, a presenter and when possible a technician. Each group member will be assigned a different set of 4 alcohol solutes contained in dropping bottles and the group will be assigned 1 organic solvent. (See the lab section page on the course website for individual alcohol solute assignments and group organic solvent assignment.) Models of water and the organic solvent molecules will be available in the laboratory. Groups choose a name Individuals build models of their alcohols Group members collaborate on developing one or more specific predictions as to trends in solubility behavior of their alcohols in water and their assigned organic solvent. Bondline structural formulas of all organic solvents and alcohol solutes are provided in Tables 1 & 2 at the end of this handout. Groups then obtain their alcohols and test predictions by doing solubility tests. After collecting data, students analyze their own data Group members then compare results within the group, reconsider their original predictions and develop a hypothesis, based on intermolecular interactions, to explain the observed trends in solubility behavior of alcohols in water and organic solvents. Finally, groups test their understanding of solubility by comparing results with another group that used a different organic solvent and explaining those additional results. H. Procedure: 1. During the first 5 minutes of the lab period, choose a group name. 2. Read the entire procedure. Manager: Assure that all group members understand the goal of the experiment and what is to be done. 3. Build models of your assigned alcohol solute molecules. 4. Record the specific waste disposal instructions for the compounds you will use for the experiment. (See the waste disposal instructions for all compounds in Tables 1 & 2) Note also that all aqueous (water) solutions of category 4 compounds are disposed in the special Aqueous-Organic waste container for Experiment 4. 5. While waiting for your other group members to complete their models, write the procedure and prepare solubility results tables to record your 2 sets of solubility results and observations (Aqueous & Organic solvents, see procedure steps 11-17) in your results section. (See the models in Tables 3 & 4) Be sure to include specific names of all compounds you are using in your procedure and to allow sufficient space between your procedure steps to accommodate each table. Solubility 3 CHEM 211 Experiment 4 6. Collaborate with your group mates to compare the models of the various solute molecules with those of your group organic solvent and water. 7. Develop specific predictions on the trend in relative solubilities of your alcohol solvents in water and in your organic solvent. 8. Present your predictions to your instructor and obtain your assigned alcohol solutes. 9. Use a set of 9 small test tubes (smallest ones in your lab tray); label them #1-#9. 10. Add 1 mL DI water to tube #1. Using a Sharpie Marker draw a horizontal line on the tube at the meniscus of the liquid. Use this tube as a template to mark the 1 mL level on the remaining tubes. Aqueous Solubility of Alcohols 11. Fill tubes #2 - #5 to the mark with distilled water. 12. Begin with test tube #1 Add one drop of the first alcohol. Agitate the tube and contents using the technique explained in the lab. Observe what happens. Continue to add the alcohol, 1 drop at a time, followed by agitation, noting what happens, until you have added a total of 10 drops. Record, in your results table, the number of drops added when you first observed cloudiness in the mixture after agitation and observe what happens when subsequent drops are added. If cloudiness is not observed record 10 drops for the mixture. 13. Repeat the process with the remaining alcohols in your set in test tubes #2, #3 & #4. Solubility of Organic Solvent in Water 14. Use test tube #5, which contains 1 mL water to repeat the process to test the solubility of your group’s assigned organic solvent in water. Record your solubility results and your observations in your aqueous solubility table. Solubility of Alcohols in Organic Solvent 15. Fill test tubes #6 - #9 to the 1 mL mark with your group’s assigned organic solvent and cork them. 16. Identify your organic solvent in your procedure. 17. Test the solubilities of each of your assigned alcohols using the organic solvent in tubes #6, #7, #8, #9 following the procedure used for testing solubility in water. (Step 12.) 18. Keep the corks on these tubes when they are not being used. 19. Keep all 9 mixtures for possible reference until all analyses and discussions are complete. 20. Create a Table of Compounds for your assigned alcohol solutes, your group organic solvent and water; include the bondline structure, molecular weight, densities and boiling point of each compound. Your table belongs on the second left-hand page of your notebook for this experiment opposite your waste disposal instructions. Individual Data Analysis 21. Analyze your solubility data and record all observations, conclusions and explanations in your results section. a. Do you recognize any trends in your data? Include your specific description of any observed trends or explanation of why you believe that there were no observable trends. b. Do your data support your group’s initial predictions? Explain why or why not? If they don’t, what new insights did you gain from your analysis of the results? Group Data Analysis 22. Group recorder: Enter all group member solubility data into a group spread sheet file on the group laptop, change the file name to the group name, save the file to the server and Solubility 4 CHEM 211 Experiment 4 print 8 copies of the data for each group member and the inter-group collaborators. (See step 25) Place your group data sheets in your data binder. All Group data will be posted on the course website at the end of the week. 23. Compare your data with that of group mates and record all observations, conclusions and explanations in your Results section. a. Are the trends or lack of trends in all individual data sets consistent with each other? Explain using specific examples to illustrate your reasoning. b. Does the entire group data set support your group’s initial predictions? Explain why or why not? If it doesn’t, what new insights did you gain from your analysis of the results? c. Use the entire group data set to develop a hypothesis to explain solubility behavior of the alcohols in water and organic solvents. Explain how your data supports your hypothesis. Use specific examples from your data to illustrate your reasoning. Inter-group Data Analysis 25. The group presenter obtains data sheets from another group, which used a different organic solvent. 26. Place the inter-group collaborator data in your data binder. 27. Compare your data with that of the inter-group collaborators’ and record all observations, conclusions and explanations in your results section. a. Rationalize the inter-group collaborators’ data on alcohol solubility in water vs. their organic solvent using your group’s hypothesis on alcohol solubility. b. What additional insights does this new data set provide? Explain. c. Reconsider your solubility hypothesis and make a clear statement of your final proposal. Explain how it can rationalize the data from both groups. Post Lab Data Analysis 28. Your group will be assigned one of the following sets (1-butanol and 2-butanol; 1-pentanol and 2-pentanol; 2-methyl-1-propanol and 2-methyl-2-propanol; 2-methyl-2butanol and 3-methyl-1-butanol). In collaboration with your group, compare the solubilities of your assigned pair of compounds (from pooled data available on the course website) in water and in all organic solvents. Use your final solubility hypothesis to explain any differences observed. Be ready to present your explanations in the Tuesday AM Lab discussion period. Table 1: Solvents Name Molecular Formula Bondline Structure Waste Disposal Category Water H2O 6 Hexane C6H14 4 Octane C8H18 4 Decane C10H22 4 Dodecane C12H26 4 Solubility 5 Table 2: Alcohol Solutes Bondline Structure CHEM 211 Experiment 4 Name Molecular formula Waste Disposal Category Methanol CH4O 6 Ethanol C2H6O 6 1-Propanol C3H8O 6 2-Propanol C3H8O 6 1-Butanol C4H10O 6 2-Butanol C4H10O 6 1-Pentanol C5H12O 4 2-pentanol C5H12O 4 1-hexanol C6H14O 4 2-hexanol C6H14O 4 2-Methyl-1-propanol C6H14O 4 2-methyl-2-propanol C4H10O 4 2-methyl-2-butanol C5H12O 4 3-Methyl-1-butanol C5H12O 4 1,2-ethanediol C2H6O2 4 1,2,3-propanetriol C3H8O3 4 Solubility 6 Table 3: Aqueous Solubility Solute Solubility* in H2O Alcohol 1 Alcohol 2 Alcohol 3 Alcohol 4 Organic Solvent * Observations the number of drops of solute required to produce a cloudy mixture in 1 mL of solvent. Table 4: Solubility in Organic Solvent Solute Solubility* in Solvent Alcohol 1 Alcohol 2 Alcohol 3 Alcohol 4 * CHEM 211 Experiment 4 Observations The number of drops of solute required to produce a cloudy mixture in 1 mL of solvent. Identify your organic solvent in the table header.