Gas Behavior

1. 4th Class Gas Behavior • Today’s Agenda: • Review use of the lab notebook. • Review understanding of molar mass & gas properties. • Develop the day’s problem. • Perform the challenge: experimentally determine the gas constant for a real gas. • Analyze results: determine the validity of using the ideal gas constant with real gases. • Discuss writing the report. Learn how to write an introduction.

2. Let’s apply Introduction • Discussed in Chapter 3 of the technique book. • You will write one before leaving today.

3. The Lab Notebook Who Cares? “Under U.S. law a patent is granted to the first to conceive the idea for the invention, not the first to apply for the patent. So a laboratory notebook is essential evidence to the date of conception.” Scientific Notebook Company “Laboratory notebooks are where inventions start, and they are the key to successful patent enforcement.” Steven Carlson, U.S Patent Attorney “…if it is not reproducible, it is not science.” YehoudaHarpaz, Chemist and Author

4. Lab horror stories sometimes involve notebooks.

5. The Lab Notebook Overall plan What and how much used • Hard to read • Don’t know what was done • Not reproducible • Not detailed Equipment set-up Procedure, cautions, color changes, and final amounts Good Bad

6. Revisiting the central goals of Chemical Analysis. Central Goals and Questions Separation: How can the substances present in the sample be separated? Quantitation: How much of substance X is in the sample? Detection: Does the sample contain substance X? Identification: What is the identity of the substance in this sample? What have we done so far?

7. Let′s think! Quantitation. How do we quantify solids & liquids? Can we use the same techniques with gases?

8. Let′s think! How can we quantify a sample of gas? By using the gas law

9. Lets consider molar mass. What do you know about the gas law? Why might we need to know the molar mass of a gas to use the gas law? Molar Mass is how we use mass to determine moles.

10. Let′s think! Gas Law Calculation Practice In your groups review your responses to the following pre-lab question and come up with a consensus answer. Part 1.   Consider a gas that has a molar mass of 100.21 g/mol.  What mass of this gas would occupy a 150 mL container under a pressure of 1.00 atmosphere and a temperature of 25 degrees centigrade? Part 2. Assume this gas is condensed to the liquid phase and the liquid has a density of 0.684 g/mL. What will the volume of the liquid be?

11. Back to the gas law. Why is it called the “Ideal” gas law?

12. Consider that you work for a company that produces pure gases for sale. You have been assigned the task to determine if it is practical to use the ideal gas constant to measure amounts of gas and what error would be introduced by doing so. In your groups: • Develop a plan for doing so.

13. Let′s practice! Complete the following table. Group A Group B You’ll need these values later in the lab.

14. Let′s think! What are the properties of those gases that we expect to exhibit the most ideal behavior? Small volume No interactions Far from boiling point For the compounds listed here predict which should show the most ideal behavior and which the least

15. Let’s apply The following compounds are available. Group A Group B Each student is responsible for one gas

16. Gas Behavior D2L-graded pre-lab assignment

17. Let′s think! Measuring a Gas Constant In your groups review your responses to the following pre-lab question and come up with a consensus answer. Using the "Procedure Outline" found in the guide and taking into consideration the "Issues for you to address" rewrite the 5-step procedure to include specifics about what you expect to be doing in the lab.    

18. Let′s think! Procedure Outline • Put an appropriate amount of liquid in the flask. • Heat the flask to vaporize all the liquid. • Measure the temperature and pressure. • Cool the flask to condense all the gas. • Determine the mass of the condensed liquid. Issues for you to address in your procedure • What is the appropriate amount of liquid? • How are you going to heat the liquid? • How are you going to quickly condense the gas? • How are you going to mass the liquid after it is condensed? • How are you going to measure the temperature of the gas? • How are you going to measure the volume of the flask? • How many times should you repeat the determination? .

19. Let′s think! • More Pointers • Remember that wet glassware will weigh more than dry glassware. • The serum cap will absorb the gases and get heavier with each trial. It is best to avoid massing the serum cap. Remove the serum cap before massing the flask and liquid. HOWEVER. Do so quickly as the liquid will begin to evaporate immediately. • A hot water bath is best prepared in a large beaker. • An ice bath is best prepared in the metal trays provided. • Those working with heptane will have to add some salt to their hot water baths to get the temperature above 100 oC.

20. Let′s explore! You have 90 minutes Your Challenge Determine the gas constant for your assigned gas. Implement the designed experimental procedure! Available resources: • Unknown gas; • Balance, thermometer, barometer; • Glassware;

21. Let′s think! Use your results to calculate a gas constant for your assigned gas and add it to the chart. As a group, • review the reported results and decide which ones you trust. Average these values and determine the standard deviation. • decide on real gas constant values for each of the gases. Compute differences between the real gas constant values and the ideal gas constant. • consider the properties of the gases evaluated and determine if there is any correlation between the differences and the properties of the gases.

22. Let’s apply Class Data

23. Looking Ahead to Next Week We will begin our study of light and how chemists use light to learn about atoms and molecules. Make sure you remember to do the pre-lab assignments in D2L.

24. The Report To be submitted BEFORE leaving class: • Raw data. A copy of all measurements and observations you collected in lab. • Calculations. Examples of the R calculation. You will now write your report for this experiment. To be submitted next week: • Introduction. Background information necessary to understand the experiment. • Results. An organized presentation of the results obtained. • Discussion. A discussion of the results obtained, their credibility and their meaning.

25. Introduction • From p. 65 of your Technique Book: • Introduction. A description of what is already known, the plan of action and expected outcomes. • From p. 71 of your Technique Book: • Introduction. A description of: • the experimental objective(s) • pertinent background information • expected outcomes, if any

26. Introduction: Outline Let′s think! In your groups: What were the major goals of today’s lab? • Extract pigments from spinach leaves. • Determine solvent mixture that, using TLC, best separates pigments in spinach extract. • Characterize the pigments on each TLC strip. (Rf values and colors).

27. Introduction: Outline Let′s think! In your groups: For each goal, list the major techniques, formulas, and chemicals used: • Extract pigments from spinach leaves. • Mortar and pestle • Acetone and hexane • Decant • Determine solvent mixture that, using TLC, best separates pigments in spinach extract. • TLC • Spinach extract • Acetone and hexane • Characterize the pigments on each TLC strip. (Rf values and colors). • Rf=Distance traveled by spot/Distance traveled by solvent

28. Let’s apply Introduction: Goal 1 In a paragraph, introduce Goal 1. Include all items on your list. • Introduce Goal 1 giving relevant background information. • Plan of action. How was Goal 1 achieved? Introduce techniques/formulas/chemicals in context. • Relevance of results.

29. Introduction: Goal 1 Spinach is known to contain a number of chlorophyll and carotenoid pigments. In order to extract the pigments from spinach leaves, they are released from plant cell walls using a mortar and pestle with sand and a mixture of acetone and hexane. Water and other unwanted aqueous substances, also released from the spinach leaves, form the bottom layer of the crude extract whereas the pigments are found in the top organic layer. The pigment-containing layer is isolated by removal with a transfer pipet.

30. Let’s apply Introduction: Goal 2 In a paragraph, introduce Goal 2. Include all items on your list. • Introduce Goal 2 giving relevant background information. • Plan of action. How was Goal 2 achieved? Introduce techniques/formulas/chemicals in context. • Relevance of results.

31. Introduction: Goal 2 TLC is a technique that separates components of a mixture based on unequal attractions between the components and the stationary and mobile phases. By using various mixtures of acetone and hexane as the mobile phase, the solvent mixture that gives the best TLC separation of pigments in spinach extract is determined.

32. Let’s apply Introduction: Goal 3 In a paragraph, introduce Goal 3. Include all items on your list. • Introduce Goal 3 giving relevant background information. • Plan of action. How was Goal 3 achieved? Introduce techniques/formulas/chemicals in context. • Relevance of results.

33. Introduction: Goal 3 In order to characterize each of the pigments, the color is observed and Rf value calculated (Rf=Distance traveled by spot/Distance traveled by solvent). The Rf value will remain constant for a substance when using a particular solvent, and can therefore be used to detect the substance in unknown mixtures.

34. Introduction: Helpful hints • Only include information that is knownbefore lab. No results, observations, etc. • 200 word maximum for one week lab. • Paragraph format. Subheadings okay. • Give items in context. No lists. • See Technique Book pp. 65, 67 and 71 for more help with writing an Introduction • See Technique Book pp. 52-55 for more help with scientific writing.

35. Let’s apply Data Presentation - Results • Organize all your measurements into tables. Include all calculated results along with measured quantities. • Include all qualitative observations that you intend to use in your discussion. Such things as problems that occurred during the data collection or odd appearances. • Organize your table to “flow”. Your presentation should lead the reader to your conclusion. • You will be graded on credibility. Your presentation must be credible. Proper use of significant figures and labeling (units) strongly impacts credibility. Data Manipulation - Calculations Decide which calculations to present and generate examples as described in technique chapter 2.

36. Let’s apply Discussion • Present the outcome to the problem posed by the experiment. Report your conclusion as to if and when it is appropriate to use the ideal gas constant when working with real gases. • Discuss your confidence in your answer Here is where you will address any problems you encountered during the experiment. Are their other possible answers? • Discuss what additional experiments might be performed to refine your answer or improve your confidence in your conclusions.