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Forgotten Genius

Classroom Activity

Learning Objective | Materials | Background | Procedure | Activity Answer | Links & Books | Standards  Print this Teacher's Guide (PDF, 10 pages)

Activity Summary
Students visit stations in the classroom to investigate physical and chemical changes and then apply what they have learned to a story about physical and chemical changes that occur in everyday life.

Learning Objectives
Students will be able to:

• differentiate between physical and chemical change.

• identify physical and chemical changes that occur in everyday life.

• whole peppercorns
• mortar and pestle
• glass of room-temperature water
• ice cubes
• paper
• matches

• copy of the "What It Takes to Change" student handout (PDF or HTML)
• copy of the "Station Instructions" student handout (PDF or HTML)
• copy of the "Data Chart" student handout (PDF or HTML)

• copy of the "Changes in Everyday Life" student handout (PDF or HTML)
• goggles
• 1 red pen
• 1 blue pen

Station Materials

Station 1
For each team

• 1 dirty penny
• 1 clean steel screw
• 60 mL white vinegar
• 8 oz clear plastic cup

For station

• 100 g salt
• plastic teaspoon
• magnifying glass

Station 2
For each team

• 1 g baking soda
• 1 film canister with lid

For station

• 10 mL vinegar
• 5 mL graduated cylinder

Station 3
For each team

• 1 g sodium polyacrylate
• 8 oz plastic cup

For station

• 500 mL water
• 50 mL graduated cylinder
• garbage bag

Station 4
For each team

• 1 antacid tablet (should contain citric acid and sodium bicarbonate)
• 1 sealable sandwich bag

For station

• 500 mL water
• 50 mL graduated cylinder
• garbage bag

Station 5
For each team

• 2 sealable sandwich bags

For station

• 300 mL purple cabbage juice
• 100 mL vinegar
• 100 g baking soda
• 20 mL graduated cylinder
• garbage bag

Station 6
For each team

• 55 g cornstarch
• paper bowl

For station

• 500 mL water
• 20 mL graduated cylinder

Background
When Percy Julian entered DePauw University he barely had a 10^th-grade education because public schools for black children stopped at eighth grade across most of the South (Julian completed an additional two years at a local teacher training school for Negroes). In addition to his university coursework, Julian took remedial classes at a local high school for two years to catch up with his white classmates. With the help and encouragement of his chemistry professor, Julian succeeded in not only catching up, but in surpassing his peers. He would go on to graduate from DePauw first in his class. In this activity, students do their own investigations into some basic principles of chemistry—they explore physical and chemical change and learn to differentiate between the two.

1. Review safety protocols. Have students wear goggles for all stations. All powders should be handled with care and neither smelled nor tasted. Students should wash their hands after they have finished with the stations. Discard dry and gelled polymers in the trash, not in the sink.

2. Set up the stations in advance of the activity. The amounts listed for the materials needed for each station are enough for 10 teams. Place station labels, paper towels, and trash bags (for disposal) at each location.

   Station 1 (chemical): Place 60 milliliters of white vinegar in each cup. Supply pennies, steel screws, salt, plastic teaspoon, and magnifying glass.

   Station 2 (chemical): Put 1 gram of baking soda in each film canister. Place vinegar, graduated cylinder, and film canister lids nearby.

   Station 3 (physical): Place 1 gram of sodium polyacrylate in each cup. Place the water and graduated cylinder nearby. (Because the polyacrylate is highly sensitive to moisture, it is best to prepare the cups just prior to the activity.)

   Station 4 (chemical): Place the antacid tablets, sealable bags, water, and graduated cylinder at the station.

   Station 5 (chemical): To make the cabbage juice, cut up a purple cabbage into small chunks, add enough water to cover, and boil until the liquid turns purple. Supply the cabbage juice, vinegar, baking soda, graduated cylinder, and sealable bags.

   Station 6 (physical): Place 55 grams of cornstarch in each bowl. Place the water and graduated cylinder nearby.

3. Organize students into teams and distribute the "What It Takes to Change," "Station Instructions," and "Data Chart" student handouts.

4. Tell students that substances can change in two ways: physically or chemically. Inform students that you are going to demonstrate three changes and have students make observations about how each substance changed following each demonstration.

5. First put ice in a glass of room-temperature water and set it down. Have students describe the glass of ice water. Next, show students the whole peppercorns and ask them to describe their physical properties. Then crush the peppercorns and have students describe the new form of the pepper. Ask students to describe how the peppercorns changed. Go through the same steps with a piece of paper and then burn it. After all the demonstrations are done, have students look at the ice water again and record their observations. Discuss with students how the changes were similar and different among the three demonstrations. Explain to students that two demonstrations showed physical change (peppercorns crushed and ice melting in water) while the other showed a chemical change (paper burned). In the cases of the ice melting in water and the paper burning, energy changes also occurred (the ice absorbed heat in order to melt and the burning paper radiated heat). Energy changes can accompany both chemical and physical changes.

6. Have students brainstorm a list of observations they could make that would indicate a physical or chemical change. (In physical changes, changes may occur in the material's properties but the chemical composition of the material is the same before and after the change. In a chemical change, one or more new substances are formed.) Stress to students that in a physical change, properties may change but molecular identities do not. Therefore, in a physical change, students should look for changes in properties, but not a change in the chemical nature of the original material. To identify a chemical change, students should look for signs like color change, production of gases or solids, and/or production of an odor.

7. Have student teams rotate through all the stations. After completing all the stations, have students work in teams to decide whether each station showed physical or chemical changes. Point out to students that more than one change may have occurred at each station.

8. Once all teams are done, as a class discuss what kind of changes each station represented and what evidence supported each type of change. (See Activity Answer for more information.) Reconcile any differences in student answers.

9. When students have completed the first part of the activity, distribute the "Changes in Everyday Life" handout to each student to help assess student understanding. Have students read the story and identify the physical and chemical changes within it. You may want to tell them that there are at least 12 changes listed. When everyone is done, review the passage as a class and discuss the changes that are listed and why they are physical or chemical.

10. As an extension, have students write their own stories that incorporate physical and chemical changes. Each story should include at least three examples of each type of change. Have classmates swap stories to try to find the changes in each other's work.

The following is a description of what is occurring at each station.

Station 1 (chemical): The mixing of the vinegar (acetic acid) and salt (sodium chloride) is a physical change. The cleaning of the penny is a chemical change. (When the pennies are put into the vinegar-salt mixture, the substance that makes the pennies appear dirty—copper oxide that formed when the copper atoms in the penny combined with the oxygen in the air—is dissolved by the weak acid.) The reactions that occur when the screw is dropped in the solution represent a chemical change (the surface of the steel screw dissolves). Evidence for change: the salt mixed into the vinegar, the penny changed color, gas bubbles formed on the screw.

Station 2 (chemical): When mixed, baking soda and vinegar form carbon dioxide gas inside the film canister. Production of this gas creates the pressure that causes the lid to pop off. Evidence for change: gas bubbles are released.

Station 3 (physical): The sodium polyacrylate absorbs the water. ( Sodium polyacrylate, which can usually be found in disposable diapers, can absorb about 800 times its weight in distilled water.) Evidence for change: gel forms.

Station 4 (chemical): As the antacid tablet—which typically includes sodium bicarbonate (baking soda) and citric acid—dissolves in water it produces a carbon dioxide gas that forms when the sodium bicarbonate encounters the acid in an aqueous solution. Evidence for change: bubbles form and bag inflates.

Station 5 (chemical): Purple cabbage juice changes color in response to changes in the overall hydrogen ion concentration (pH) of the solution. Acids such as acetic acid (vinegar) donate hydrogen ions to the purple solution, which turns the purple cabbage pigment red or pink. Bases such as sodium bicarbonate (baking soda) accept hydrogen ions when added to purple cabbage juice, causing the pigment to become blue or blue-green. Evidence for change: the purple cabbage juice changes color.

Station 6 (physical): The cornstarch mixes with water and becomes more solid. The mixture is a colloidal suspension—the cornstarch is not dissolved but mixed into a suspension that doesn't settle out. Evidence for change: when mixed with water, cornstarch has properties not present when it is in powder form.

Just One of Those Days
Students may note additional changes that are not mentioned here, such as the biting of the apple, the cracking of the eggs, or the jelly and butter mixing as being physical changes. Accept all reasonable answers.

sour milk: chemical
rusty tack: chemical
decaying plants: chemical
saltwater evaporation: physical
ice melting: physical
glass breaking: physical
apple browning: chemical
whipping eggs: physical
cooking eggs: chemical
browning bread: chemical
melting butter: physical
dyeing hair: chemical

Web Sites

NOVA—Forgotten Genius
www.pbs.org/nova/julian/
Offers features about Julian's role as a civil rights trailblazer, a speech Julian made, a time line of his chemical achievements, stories from those who knew him, information about plants that have been synthesized into chemicals, a way to make steroids online, and more.

General Chemistry Online!
antoine.frostburg.edu/chem/senese/101/index.shtml
Provides an overview of chemistry basics.

Science Alive! The Life and Science of Percy Julian
www.chemheritage.org/scialive/julian
Provides information about Julian's life and career, with material on his childhood, college years, scientific discoveries, and civil rights work.

Books

A to Z of Chemists
by Elizabeth H. Oakes. Facts on File, 2002.
Tells the stories of 150 historical and contemporary chemists.

Chemical Achievers: The Human Face of the Chemical Sciences
by Mary Ellen Bowden. Chemical Heritage Foundation, 1997.
Provides teachers with photos and biographies of 80 chemists, many of whom are people of color.

The Joy of Chemistry: The Amazing Science of Familiar Things
by Cathy Cobb. Prometheus Books, 2005.
Includes science and history, and connects chemistry to the real world.

The "What It Takes to Change" activity aligns with the following National Science Education Standards (see books.nap.edu/html/nses).

Grades 5-8
Physical Science
Properties and changes of properties in matter

Classroom Activity Author
Developed by WGBH Educational Outreach staff.