Chemistry XXI Lab Session 13 How do we synthesize new substances? (Two-Week Experiment)

Chemistry XXI Instructor & Course Evaluation: In the past we have found our students’ remarks and suggestions to be very helpful. This input has led to a number of changes in our experiments and our programs. For the benefit of future students we ask for your thoughtful comments. Before We Start What do you think?

Chemistry XXI Please be as specific as possible and keep the following in mind: A.This information will be used not only to evaluate your instructor but also to evaluate the course. B.Your instructor will not be allowed to see your comments until AFTER grades have been submitted to the Registrar. C. ALL evaluations are read by at least three members of the department. D. We need to know what we are doing right as well as how we can improve. Instructor & Course Evaluation

Chemistry XXI The End is Near(ing) VTs Day No classes 1213 VTs Day Make up 16 CHEM 151 Exam Final day to do lab No Labs 24 No Labs 25 No Labs 26 Thanksgiving No classes 27 No classes 30 Lab Finals Week 1 December Lab Finals Week 2 Lab Finals Week 3 Lab Finals Week 4 7 CHEM 151 Exam 4 89 Last Day 10 DEAD DAY No Classes 11 Finals Begin

Chemistry XXI What are we doing? Last week we started exploring some techniques used to “synthesize” new substances. Transformation How do I change it? Analysis What is this? Modeling How do I explain it? Synthesis How do I make it?

Chemistry XXI Your Challenge Imagine that you work for a drug company interested in testing a new procedure to synthesize aspirin. You have been asked to evaluate whether the procedure is feasible and marketable.

Chemistry XXI Initial Ideas In your groups, summarize what you did last week and the results that you got. Acid Catalyst What was your percent yield? What problems did you encounter? What do you still need to do?

Chemistry XXI Your central problem this week is to assess the purity of your aspirin with the intent of making the argument that it is pure enough to market. Purity How do you plan to assess the purity of your product. What techniques would be useful? Melting point, TLC, and Titration

Chemistry XXI Different Tests Why do we need to perform three different tests to analyze the purity of our product? The test allow us to answer different questions: Melting Point  Are there impurities? TLC  How many? Titration  How Much?

Chemistry XXI In your groups:  Define melting point  Define melting point range.  Explain why melting point can be used to identify a substance.  Explain how it can be used to determine the purity of a substance.  Create an outline of the steps required to obtain a melting point range using the Mel-temp7. Melting Point

Chemistry XXI Safety Precautions  The melting point device can get very hot. Be careful to not burn yourself.  The thermometer must not be left in the melting point device once measurements have been made.

Chemistry XXI Two different ones:  Closed-ended tubes are for melting point.  Open ended tubes are for TLC.  Do not mix them up!  Don’t forget – they’re GLASS WASTE! Capillary Tubes

Chemistry XXI TLC In your groups:  Define TLC.  Explain how TLC can help confirm that you really made aspirin.  Explain how TLC can be used to determine the purity of your aspirin.  Create an outline of the steps required to successfully chromatograph the three samples.

Chemistry XXI Seeing Spots Unlike the TLC of spinach leaf extract, the aspirin is colorless. Two methods will be used to make the spots visible. What are the the two methods?

Chemistry XXI Seeing Spots Safely Iodine – Stains the skin. Fumes are acrid UV Light – Can damage the retina. Avoid looking at the lamp.

Chemistry XXI First Challenge Analyze the purity of your product using Melting Point determination and TLC analysis. Available resources:  Melting point apparatus TLC plates.  TLC plates.  Solvent  Your aspirin  reagent grade aspirin and an aspirin tablet. You have 60 minutes

Chemistry XXI Claims and Evidence Based on the results, present your major claims about the purity of your product.  Are their claims clear?  Is the evidence reliable?  Is the evidence appropriate to support the claims?  How do you explain the results?

Chemistry XXI How much is there? C 9 H 8 O 4 + NaOH  C 9 H 7 O 4 Na + H 2 O Sodium Acetyl Salicylate Sodium Hydroxide Acetyl salicylic acid (Aspirin) Water We can quantify how much Aspirin is there by making it react with a known amount of another substance (NaOH): If we determine the moles of NaOH that react, we can determine the mass of Aspirin present in the sample. The process is called Titration.

Chemistry XXI Titration Unknown Amount n u Known concentration C At the endpoint of a titration, the moles of known added equals the moles of unknown in the sample (if 1:1 ratio). n u = V f C Measured V f End point Indicator (signals endpoint)

Chemistry XXI The Buret Time for a demonstration

Chemistry XXI Final Challenge Titrate a small sample of your aspirin to analyze its purity. You have 60 minutes Available resources:  Standardized solution of NaOH;  Glassware;  Buret;  Phenolphthalein indicator. Titrate a part of your aspirin tablet.

Chemistry XXI How much is there? C 9 H 8 O 4 + NaOH  C 9 H 7 O 4 Na + H 2 O Sodium Acetyl Salicylate Sodium Hydroxide Acetyl salicylic acid (Aspirin) Water Based on your results, and on this titration equation, calculate the actual percent of aspirin in your sample.

Chemistry XXI Claims and Evidence Based on the results of ALL of your tests, present your major claims about the purity of your product.  Are their claims clear?  Is the evidence reliable?  Is the evidence appropriate to support the claims?  How do you explain the results?

Chemistry XXI  What did you learn from doing your experiment?  How would you improve what you did?  How have your ideas changed as a result of this lab?  What do you not completely understand?  What new questions do you have? Final Reflections

Chemistry XXI  Beginning questions (2 p);  Safety Considerations (2 p);  Procedures and Tests (2 p);  Data, calculations, and representations (6 p);  Claims (2 p);  Evidence and Analysis (6 p);  Reflections and additional questions (10 p). Your Report

Chemistry XXI Is this process feasible and marketable? What is your evidence? How much would it cost to produce a 500 mg aspirin tablet using this method? How could improve the process (Feasibility and Marketability)? In Your Report Your report should provide answers to these questions: