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**Grades:** 6-8

**Author:** Connie Hubbard, Sandra Van Natta, AGPA staff

**Source:** Original

A nanometer is one billionth (1 x 10-9) of a meter which can be about 3 to 5 atoms in width. Electrospun nanofibers produced from polymer solutions are being used in unique ways by scientists. Nanotechnology allows the manipulation of matter, atom by atom at the "nanoscale." Properties of these materials are amplified due to the fact that many fibers can fit into a very small space. Scientists have found many unique ways to use such fibers from producing new materials capable of blocking moisture, removing of toxins from both water and air, delivering medicines to a specific region in or on the body, and tissue scaffolding. The possibilities are endless as scientists and inventors produce new products formed from these extremely small fibers.

In this investigation students will determine the advantages of going "small" by comparing the amount of chocolate syrup coating on a large diameter pretzel to that of an equal volume of smaller pretzels coated with chocolate. Students will learn what happens to the surface area as the diameter gets smaller and smaller. Students will determine what advantages exist in making the size (diameter) of a pretzel smaller. Students will make the comparison by massing a cup of chocolate syrup before and after dipping the pretzel(s). Students will use their data to support their conclusions. The lesson contains a PowerPoint review of the metric system with pictures to help students visualize large and small number lengths. Using a second PowerPoint set of slides in the elaboration, the teacher can relate the activity to the new field of nanotechnology and discuss with students why it is advantageous for newly developed materials to be so small. This often has to do with the large surface area available on nanosized particles and fibers.

**What should students know as a result of this lesson?**

- Students will explain that smaller objects that collectively have the same volume as a larger object will have a larger collective surface provided the length is constant. The smaller the object (pretzel, fiber, etc.), the greater the surface area (i.e. The more surface you can coat with whatever!)
- Students should conclude that more chocolate can coat an equal volume of smaller pretzels.
- Students should be able to extend this concept to other situations such as coating fibers with medicines (stents in heart arteries, new bandages, and coatings on slow-release patches.)
- Students should discuss why it can be advantageous to have smaller objects such as nanofibers as opposed to our traditional microfibers. A fiber is essentially a cylinder so the volume can be found by taking the cross-sectional area and multiplying by the length (height of the pretzels). The surface area can be approximated by multiplying the circumference of the pretzel by its length. Then the surface area is divided by the volume. (Since the volumes of the large pretzel and the group of smaller pretzels are estimated to be the same, you can calculate just surface areas by multiplying the circumference of the pretzel by the chosen constant length. Remember to add the surface areas of the smaller pretzels together.) This would represent a close approximation of the surface area-to-volume ratio.
- Students will be able to explain that a smaller diameter on an object results in a larger surface area when compared to its volume.

**What should the students be able to do as a result of this lesson?**

- Some students may be able to calculate mathematical equations, which prove this concept.
- Students should be able to mass a cup containing chocolate several times and accurately record appropriate data.
- Students should be able to subtract successive weightings to obtain the amount of chocolate deposited on individual pretzels.
- Students will be able to extend this concept to real world situations such as the need for nano-sized objects.
- Students will be able to extend this concept to other situations such as coating fibers with medicines (stents in heart arteries, new bandages, and coatings on slow-release patches.)

Per group of students:

- 1 eight-ounce paper cup containing chocolate syrup (about half full)
- 1 large pretzel
- About 3 small pretzels
- Paper towels
- Paper plates
- A balance measuring to one-tenth gram (0.1 gram)

**Engagement**

Begin the lesson by showing students pictures (or actual objects) of first-generation technologies and more recent examples. Pictures of a video-tape along side a DVD and a television that used cathode ray tubes along side a flat screen television are available by clicking here. Discuss with the students these examples of developments in electronics products (technologies) that have become possible due to our new ability to "do more" in ever smaller spaces. Explain to students that in this lesson they will be exploring the advantages of going small and learning about application in the new field of nanotechnology.

__The teacher should begin with a demonstration:__

*Teacher Demo:* Dip 1 small diameter pretzel in chocolate syrup and then do the same for one large one large pretzel. Dip to the same depth. Ask students which would have the greater amount of chocolate on the surface of the pretzels. Most will say that the larger pretzel will have the most chocolate. Then say "What if I use 3 small pretzels which combined are about the same diameter as the large pretzel? Which will have more chocolate on the surface?" __Have students write down their prediction__. Then introduce students to the laboratory activity where they will gather mass measurements to determine which group has the greater amount of chocolate.

*Assessment* A quick assessment of understanding can be done by taking a hand count of ideas. Ask how many students believe that there will be no difference; how many think the larger pretzel will contain more chocolate; and, how many think the smaller pretzels will contain more chocolate.

**Exploration**

In the following activity students will determine what advantages exists in making the size (diameter) of pretzel smaller. Students will compare the amount of chocolate covering a large diameter pretzel with that of smaller pretzels that take up about the same diameter. Students will make the comparison by massing their cup of chocolate before and after they dip the pretzel(s) in chocolate.

__Procedure: Give the following directions to the students__

- Weigh chocolate syrup and paper cup together. Write down your value here _____ grams.
- Obtain one large pretzel and 3-4 small pretzels. Check with your teacher to obtain the correct number of smaller pretzels to be equal in diameter to the larger pretzel.
- Measure from one end of each pretzel to a distance of 5 centimeters and mark the location with a marker.
- Dip the large pretzel in the syrup up to the 5 centimeter mark. Lift the pretzel up and over the cup. Allow it to stop dripping. Lay the pretzel on the paper towel.
- Weigh your cup again. The mass is now _____ grams. The difference between the first weighing and the second is equal to the amount of chocolate on the pretzel. The difference is equal to _____ grams.
- Dip each small pretzel to the 5 centimeter mark as you did before. Wait for it to stop dripping. Repeat for the other small pretzels you have. Lay them on the paper towel.
- Weigh the cup of chocolate again. Its mass is _____ grams. Take the mass of the cup before you dipped the three smaller pretzels (in number 5) and subtract the final weighing from it. What will this equal in grams _____? What does this value stand for?
- Compare your values with 2 other lab groups. How does your data compare?

*Assessment* Monitor the students as they work to be sure that they are following procedures and working safely.

**Explanation**

Let students suggest what should be in the table. Remind them to use labels. Have students post their data on the board or overhead projector. They can easily find their mistakes that way. Doing this in a constructive manner builds trust within the classroom. Allow students to have their work checked before posting, if desired by the student.

A sample data table could be:

As students look at their class data, they can average the chocolate coatings for each group. Point out that scientists draw conclusions based on as much data as possible. If a students' individual data does not match the class average (which will be typical), this will give the teacher an opportunity to discuss trends and probability, experimental design and sources of error.

Review the metric system of measurement and the prefixes that when affixed to "meter" describe very large to very small units of length. Show the PowerPoint presentation entitled, What is the Meaning of "Nano" in Nanotechnology?

*Assessment* Student should answer the following questions as written responses to the lab data:

- What is the average chocolate coating for the large pretzel?
- What is the average chocolate coating for the group of small pretzels?
- Do the averages support your original prediction? Support your answer.
- Write a few sentences describing what you discovered about the amount of chocolate on the large pretzel compared to the three smaller pretzels.

**Elaboration**

**A.** Use one large paper straw and a number of smaller straws equivalent in volume to help students understand surface area compared to volume. Since the volume is constant, you can focus just on the surface area of the straws. The lengths of the straws are also constant. Cut the straws open with an exacto knife, flatten them and tape them to an overhead transparency. Have student volunteers measure the length and width dimensions. The class can calculate the areas by multiplying the length times the width. Data will show an increase in surface area when the areas of the smaller straws are added together and compared with the larger straw's surface area.

**B.** Conduct a discussion of the applications of nanotechnology after showing the PowerPoint presentation, Nanotechnology and Nanofibers.

*Assessment*

- Ask students which will contain more spaghetti sauce, angel hair pasta or linguini per cupful. (Some students may not know what these noodles look like so you should bring in samples.)
- Asked students which bandage will contain more medicine, one made of microfibers coated with medicine or one made of nanofibers coated with medicine.

Students should have some knowledge of metric units and prefixes.

Students should know how to correctly mass objects and record these values in a data table.

Students should be able to locate and describe the diameter, length, surface area and volume of an object.

- Using analogies
- Scientific literacy
- Conceptual understanding of problem solving
- Real world applications
- Use of models

**NGSS Standards:**

- MS-PS1-1 Develop models to describe the atomic composition of simple molecules and extended structures.
- MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
- MS-PS1-3 Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.

**Common Core Standards:**

- RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
- RST.6-8.3 Follow preciesly a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
- WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.

**National Standards:**

- Physical Science Content Standard (6-8)
- Mathematics (6-8)

**Ohio Standards:**

- Physics Content: Benchmark A (6-8)
- Science and Technology: Benchmark A (6-8)

Metric prefixes (students will need to have nano and micro defined)

Define nanofiber

Metric measurement - using an electronic balance

Recording data correctly with the appropriate unit

Geometric concepts: volume, surface area, diameter

Remind students not to eat pretzels or the chocolate used in the experiment.

Nanotechnology allows the manipulation of matter, atom by atom at the "nanoscale." Properties of these materials are amplified due to the fact that many fibers can fit into a very small space. Scientists have found many unique ways to use such fibers from producing new materials capable of blocking moisture, removing of toxins from both water and air, delivering medicines to a specific region in or on the body, and tissue scaffolding. The possibilities are endless as scientists and inventors produce new products formed from these extremely small fibers.

Additional information about nanotechnology and nanofibers is found in the PowerPoint presentation, Nanotechnology and Nanofibers.

Both performance and written assessments within this lesson will allow the teacher to determine student learning. Students should be able to measure correctly using metric instruments. They must graph variables and answer questions which demonstrate understanding of the concepts.

**Grouping Suggestions:** Recommended for groups of 2 or 3 students.

**Pacing/Suggested Time:** 2-lab periods of 43 minutes; Reflection and Discussion (10-15 minutes)