1. Chemistry XXI Unit 1 How do we analyze a system? Modeling and Measurement

2. Chemistry XXI Lab Session 4 How do we use models to differentiate substances?

3. Chemistry XXI The Challenge Three volatile solvents have been found in different containers in an illegal drugs lab. Based on prior experiences, you infer the potential identity of these substances: Butanone C4H8OC4H8O Ethanol C2H6OC2H6O Hexane C 6 H 14 How can you determine the identity of the solvent in each container?

4. Chemistry XXI So, what do we need to measure to determine m NA for a gas sample? How can these properties be measured? Your Ideas According to the ideal gas model: Discuss in your groups the actual procedure you propose to follow. Available resources:  Sample of known substance (acetone, K 2 );  Balance, thermometer, barometer;  Hot and cold baths;  Glassware;

5. Chemistry XXI Your Plan How are you planning to generate the sample of gas? How are you planning to measure its temperature? How are you planning to measure its pressure? How are you planning to measure its mass? How are you planning to measure its volume? WHY? Where are the most likely sources of error? How can you plan to avoid or minimize them?

6. Chemistry XXI Apply your ideas and experimental skills to determine the molar mass of the known substance provided. Available resources:  Sample of known substance (acetone, K 2 );  Balance, thermometer, barometer;  Hot and cold baths;  Glassware; Make sure to repeat your measurements at least two times! You have 45 minutes Skill Building Tests

7. Chemistry XXI Present your measurements and calculations to the class. Decide as a group which data should be shared to facilitate the analysis. Share Results Acetone (T b = 56.5 o C) m NA = 58.08 g/mol C3H6OC3H6O

8. Chemistry XXI Some Reflections As a group  Discuss the difference, if any, between the average experimental result and the actual molar mass of the gas. How do you explain these differences?  Discuss what the standard deviation tells you about the precision of the average value.  How could you modify your experimental procedure to improve the accuracy and/or the precision of your results?  How could you modify your model to improve its usefulness in identifying unknown substances?

9. Chemistry XXI Your Challenge Three volatile solvents have been found in different containers in an illegal drugs lab. Based on prior experiences, you infer the potential identity of these substances: Butanone (T b = 80.0 o C) C4H8OC4H8O Ethanol (T b = 78.4 o C) C2H6OC2H6O Hexane (T b = 69.0 o C) C 6 H 14 m NA = 72.11 g/mol m NA = 46.07 g/mol m NA = 86.17 g/mol How can you determine the identity of the solvent in each container?

10. Chemistry XXI Beginning Questions What questions would your group need to answer to face the challenge? Discuss with the whole group the best strategy to find the identity of the three unknowns. GroupQuestion 1 2 3 4 5 6

11. Chemistry XXI Your Real Challenge Design and implement an experimental procedure that will allow you determine the identity of the three unknowns. You have 60 minutes Available resources:  Samples of unknown substances (K 1, A 1, C 1 );  Balance, thermometer, barometer;  Hot and cold baths;  Glassware;

12. Chemistry XXI Claims and Evidence Based on the results of your experiments, present your major claims and the evidence that you have to support the answer to your question.  Is the group answering their beginning question?  Are their claims clear?  Is the evidence reliable?  Is the evidence appropriate to support the claims?  How do you explain your results? Butanone Ethanol Hexane m NA = 72.11 g/mol m NA = 46.07 g/mol m NA = 86.17 g/mol

13. Chemistry XXI The Identity How do you explain the differences? Butanone (T b = 80.0 o C) C4H8OC4H8O m NA = 72.11 g/molEthanol (T b = 78.4 o C) C2H6OC2H6O m NA = 46.07 g/mol Hexane (T b = 69.0 o C) C 6 H 14 m NA = 86.17 g/mol K1K1 A1A1 C1C1

14. 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

15. Chemistry XXI  Beginning questions (2 p): What questions guided your explorations?  Safety Considerations (2 p): What did you do to stay safe in the lab?  Procedures and Tests (2 p): What experiments did you do to answer your questions?  Data, calculations, and representations (6 p): What observations did you make? What data did you collect? What calculations and representations helped you make sense of the data? Your Report

16. Chemistry XXI  Claims (2 p): What can you claim to answer your questions?  Evidence and Analysis (6 p): How did you interpret your results to support your claims?  Reflections and additional questions (10 p): What did you learn? What do you not completely understand? How have your ideas changed as a result of this lab? What new questions do you have? How would you improve what you did? Your Report

17. Chemistry XXI  Post-Laboratory Questions: Your Report 1. Discuss what your results indicate about the use of the ideal gas law to determine the molar mass of any gas. Your discussion should include your judgment of the practicality of the technique and the validity of the basic assumptions (ideal gas behavior). 2. Suggest at least one change that you think would produce better results.

18. Chemistry XXI Lab Session 5 What is the relationship between a substance’s color and the light it absorbs?

19. Chemistry XXI The Challenge A local business produces colored salt solutions for use in baths and spas. Your team of chemists has been hired to conduct research and provide suggestions for new product colors. How can you determine how the color depends on the type of light that is absorbed or transmitted? At this time, the business wants to better understand the relationship between salt solution color and the absorption or transmission of visible light.