Oleic Acid Teachers Guide

Oleic Acid Teacher’s Guide (Large Tray Option) 1

STEM ED/CHM Nanotechnology at UMass Amherst

A Teacher’s Guide for the Oleic Acid Thin Film Activity

The Nanoscale Context: Students apply an understanding of relationships among surface, area, depth, and volume in order to calculate the nanoscale thickness of a thin film of oleic acid (or olive oil) that forms on the surface of tray of water.

The STEM Context: This activity can be integrated into a study of measurement systems, miscibility of liquids, and intermolecular forces

National Science Education Learning Standards Examples  Science as Inquiry Standard; Grade 5-8 (Page 145): “Use appropriate tools and techniques to gather, analyze, and interpret data.”  Physical Science Content Standard B; Grades 9-12 (Page 179): All students should develop an understanding that “The physical properties of compounds reflect the nature of the interactions among its molecules……” Massachusetts Science and Technology/Engineering Learning Standards Examples  Physical Science; Grades 6-8 (Page 67): “Recognize that the measurement of volume and mass requires understanding of the sensitivity of measurement tools …..and knowledge and use of significant digits.”  Chemistry, High School (page 70): “Identify how hydrogen bonding in water affects a variety of physical, chemical, and biological phenomena…….” Massachusetts Mathematics Learning Standard Example  Measurement; Grades 7-8 (Page 65); “Demonstrate an understanding of the concepts and apply formulas and procedures for determining measures……”  Measurement; Grades 9-10 (Page 75); “Describe the effects of approximate error in measurement and rounding on measurements and on computed values from measurements.”

Materials for the Activity  Oleic acid may be purchased from suppliers (e.g. Sargent-Welch: #WLC94631-06) Olive oil or other household oils can also be used.  Isopropyl alcohol.  Baby power or fine chalk dust can be used to confine the thin layer.  Dinner size or large tray  10 cm3 and 25 cm3 or 50 cm3 graduated cylinders.  Medicine droppers.  Rulers, calculators, paper towels.  Jugs of water to fill trays with water and large plastic bowls to empty trays.  Activity document, calculation worksheet (with or without calculation hints). Oleic Acid Teacher’s Guide (Large Tray Option) 2

Possible Teaching Strategies

Show segments of a PowerPoint at various times in the activity  Show Slides 1 through 12 of the PowerPoint presentation prior to the activity.  You may want to discuss relationships among the volume, thickness and area of the top surface of a disc shown in slide 5.  Show Slide 13 and 14 during a discussion of the calculation of the dimensions of the thin film.  Slides 15 through 21 outlines the process of the formation of a thin film. This can be discussed after students have formed the thin film and completed their calculation of the thickness of the film.  Slide 22 poses questions for students.  Slide 23 and 24 present the Big Ideas of Self Assembly.  Slides 25, 26 and 27 provide information for teachers. . Discuss Experimental Procedures:  Students will need to use a consistent strategy for reading the meniscus of the liquid in graduated cylinders. Students will be using a 10 mL and 25 mL graduated cylinder if they are working with trays. They will use a 10 mL and 50 mL graduated cylinders if they are working with smaller trays.  A solution must be thoroughly mixed before removing one cm3 needed to make a more dilute solution.

If appropriate, discuss the chemical structures and properties of water, oleic acid, and alcohol.  Oleic acid dissolves in alcohol. The alcohol dissolves in water but the oil does not dissolve in water leaving a thin film on the surface of the water.  The hydrophobic end of an oleic acid molecule has the structure of a hydrocarbon. The hydrophilic end has the structure of a carboxylic acid.  The hydrophilic end of oleic acid includes an oxygen atom. The result in a very unequal sharing of electrons with an adjacent atoms and the formation of partial positive and negative charges.  The hydrophilic end of an oleic acid molecule includes highly electronegative oxygen atoms and is asymmetrical. The hydrophobic end of the oleic acid molecule does not include highly electronegative elements and is symmetrical.  Intermolecular forces referred to as hydrogen bonding describe the attractions between the carboxylic end of the oleic acid molecules and the water in the tray.  Intermolecular forces referred to as van der Wall forces describe the interactions between the hydrophobic ends of the oleic acid molecules as the oleic acid molecules align themselves vertically on the surface of water.  Oleic acid is a pure substance and the thickness of a monolayer will also be the length of an oleic acid molecule. Household oils are a mixture and the thickness of the monolayer will then be the average length of molecules in the mixture. Oleic Acid Teacher’s Guide (Large Tray Option) 3

Demonstrate the process of making a very dilute solution when using a large tray.  Pour 1 mL of grape juice concentrate into a 10 mL graduated cylinder. Use Caution: Grape juice concentrate can permanently stain surfaces and clothing.  Pour the 1 mL of concentrate into a 25 mL graduated cylinder. Move the solution back and forth between the graduated cylinder and another container. Important Note: If you are using a dinner size tray you need to use a 50 mL graduated cylinder to make 40 mL solutions.  Show the students the very pale purple color of the first solution.  Ask students to calculate the volume of grape juice concentrate in just 1 mL of the first solution. (1/25th of a mL or 0.04 mL)  Pour 1 mL of the first solution into a 25 mL graduated. Add water to make 25 mL of a second solution. Thoroughly mix the solution.  Show students the second solution and ask if the think that there is any concentrate in the second solution even though it will appear to be clear.  Put 1 mL of the second solution into a 10 mL graduated cylinder.  Ask students to calculate the volume of concentrate in just 1 mL of the second solution. (1/25th of 0.04 mL or 0.0016 mL)  Pour the 1 mL of the second solution into a small cup.  Use a dropper to count the number of drops it takes to make 1 mL of the second solution in a 10 mL graduated cylinder. (For Example: 42 drops).  Ask students to calculate the volume of concentrate in just one drop of the second solution. (In this example it is 1/42 of 0,0016 mL or 0.000038 mL)  Students will then be more aware that they will be dropping a very, very small volume of oleic acid (or oil) onto the surface of water in a tray.

Prepare Solutions for Students to Use  Multiply the volumes used in the preceding direction by the number of student groups. This will requires using larger graduated cylinders or graduated beakers.  Store small amounts of solution for each group in containers that can be cloased.

Demonstrate how to calculate the thickness of a somewhat circular thin film.  Use silly putty to form a cylinder. Ask student how they would you calculate the volume of the cylinder of silly putty. The formula is V = ∏R2h.  Then ask students how they could calculate the thickness of the cylinder if they knew what the volume was. Using algebra they would solve for h and the new formula would be h = V / ∏R2.  Flatten the cylinder into a flat, circular disc.  Ask students if you had changed the volume of the silly putty when you flattened it. They will probably recognize that the volume did not change.  Discuss how they will be using this version of the formula to calculate the thickness of a thin film of oleic acid (or an oil).  Ask them what they thick the value for h will be if they use a small volume of a liquid that spreads over a large area. Oleic Acid Teacher’s Guide (Large Tray Option) 4

Examples of Student Responses to Questions Question 1: How does your value for the thickness of the thin film compare with generally accepted the length of 1.97 nanometers for oleic acid molecule? Student answers will vary. Many values will be larger or smaller than the generally accepted values. Question 2: Why might there be a difference between the thickness of the thin film that you made and the generally accepted length of an oleic acid molecule? When student values are larger, that can mean that the thin film consisted of multiple layers of oleic acid. When values are smaller, that can mean that gaps in the thin film developed as the oleic acid spread to form a thin film. Question 3: What are some sources of experimental error in the procedure you followed? Answers will vary and include inconsistencies in reading the meniscus of the liquid in graduated cylinders, errors in counting the number of drops in a cubic centimeter of a solution, difficulty in determining the average diameters of a somewhat circular thin film, errors in multiplication or division, etc. Question 4: How can experimental error for this activity be reduced? Answers will vary depending on what they have cited as sources of error. Question 5: What area of the lake’s surface would be covered by a thin film if 1.0 liter of pure oleic acid were accidentally spilled onto the surface of a lake? Set up a proportion to calculate the number of drops of oleic acid in a liter of pure oleic acid: 1.0 drop / 0.00004 ml = x drops / 1000 mL. For this example, there would be 25,000,000 (2.5 x 107) drops per liter. As a result, the area of the thin film would be 2.5 x 107 times larger that the area from the activity.  For this example, 362.87 cm2 x (2.5 x 107) = 9.07 x 109 cm2. There are 10,000 cm2 (1.0 x 104) in a square meter. The area would equal 9.07 x 105 m2. There are 1 x 106 m2 in a square kilometer. Therefore, based on this group’s results, the area of a thin film of 1.0 liter of oleic acid would equal 0.907 square kilometers.

Oleic Acid Thin Film Resources: Web sites that provide information about oleic acid thin films include:  www.chymist.com/size%20fatty%20 acid .pdf  http://chem.lapeer.org/Chem1Docs/OleicAcidLab.html

A book, entitled Ben Franklin Stilled The Waves, written by Charles Tanford and published by Oxford Press included a full description of Franklin’s observations and experimentation with thin films of oil.  http://www.barnesandnoble.com/w/ben-franklin-stilled-the-waves-charles- tanford/1005918000?ean=9780192804945  http://www.amazon.com/Ben-Franklin-Stilled-Waves- Reflections/dp/1422351297