Dye Chemistry Subject Area: Chemistry Grade Level: Middle School Chemistry Lesson Title: Dye Chemistry National Science Education Standards: Science as Inquiry: 5–8 Properties and Changes of Matter: 5–8 History and Nature of Science: 5–8 Science in Personal and Social Perspectives: 5–8 Suggested Prior Knowledge: concepts of molecules, acids and bases, pH, chemical reactions, and solutions Purpose: To understand how dyes color things such as eggs or fabrics, to observe a chemical reaction in which a dye bonds to a surface or fabric Key Vocabulary: dye—soluble colored compounds that react with, for example, egg shells or fabric, to impart color extract—a substance made by a part of a raw material, often by using a solvent such as ethanol or water; a solution or infusion made by drawing out from any substance that which gives it its essential and characteristic virtue extraction—the process of obtaining something from a mixture or compound by chemical or mechanical means Objectives: 1. Students will investigate natural dyes and what colors they give to eggs or fabric. 2. Students will design and carry out an investigation to determine which natural products will produce the desired color on eggs or fabric. 3. Students will draw conclusions concerning which sources produce which dyes. Materials: - Safety goggles - Natural dye sources (attached list) - Hard-boiled eggs (or cotton fabric) Dye Chemistry (Middle School Level) 1 - Wax pencils or crayons - Vinegar - Sodium carbonate - Coffee filters - Hot plate - Spoons Procedure: 1. Begin with a discussion of the history of dyes. Dyes have been used to color fabric and other things for thousands of years. Early Romans dyed wool fabric, and indigo (think blue jeans) has been used as a dye since early Roman times. Natural and synthetic dyes are still widely used to color fabrics, paper, and even skin (henna). Some dyes (like many sold in stores) just color the fabric and wash out a little each time the fabric is washed. Other dyes chemically attach to the molecules of the fabric, and can never wash out. 2. Discuss with students the concepts of chemical reactions, specifically reactions in which color changes. Dyes are commonly used in the U.S. in many different ways. Synthetic dyes are used in everyday foods for their bright colors and low cost; yet they are also currently being studied by the FDA and other groups because of concerns that these synthetic dyes contribute or even cause behavioral changes such as hyperactivity and inattention in children. These synthetic food dyes are not just used in snack foods, they are in a surprising array of everyday “healthy” food choices such as yogurt, macaroni and cheese, and pickles. 3. Explain that students will work in cooperative groups to design and carry out an investigation into natural dyes that could be used (as they are in the U.K.) to replace these synthetic dyes in our foods. Students will use these natural dyes to dye a hard-boiled egg. This is a good way to tie into the spring season but this lesson can also be used with cotton fabric (handkerchief). Some of these dyes will react better in acidic solutions and others in basic solutions. Begin with a leading question, and follow up: How does a solute dissolve? How can we design an investigation to determine which of these natural products will impart the brightest and most varied colors to our eggs/fabric? Could we also color paper or other kinds of fabric with these dyes? What effect does changing the acidity of the dye solution (adding vinegar or sodium carbonate) have? What happens if we decorate the egg or fabric with crayon first? 4. Guide students to develop a hypothesis and identify the variables they will test. Work with students to determine what will be their control and what will be the independent and dependent variables in their experiments. Students should be limited to a specific number of dyes with which to work. Students should determine a list of materials they will need to carry out their investigation and they should develop an appropriate data table. 5. Ensure that students outline the steps of their procedure carefully. Work with students to design a valid investigation into these natural dyes, a procedure similar to the one outlined in this lesson plan or something of their own design. Some leading questions include the following: Dye Chemistry (Middle School Level) 2 How will you extract the dye from the source? How will you color the eggs? Can we mix sources to get different colors? Can we double dye (dye first with one color then again with a different color) to get mixed colors? Are there other ways to make designs on the egg/fabric? 6. Lab safety equipment and protocols should be followed. Caution students that these dyes may also dye their skin and clothing. They should avoid getting the dye solutions on their skin or clothing. Goggles are mandatory; gloves and aprons may be a good idea. Tie back hair and avoid loose clothing near hot plates. T-shirts can often be used to pull over students’ clothing for protection. 7. Some general procedures that could be used include the following: a. Obtain several hard-boiled eggs to color. b. Place four 400 mL beakers 2/3 full of water on hot plates and heat these to boiling. Add a small amount (5 mL) of vinegar to each beaker to acidify the water. c. Place a different natural dye source in each beaker to color the water. d. Add one egg to each beaker of boiling dye. e. Reduce heat to simmer for about 15 minutes. Longer boiling time will impart a deeper color in most cases. Using more dye material may also give more color. f. Some variations to try include the following: Leaving eggs in cold dye in a refrigerator overnight may give darker colors. This can be done by the removing eggs from the dye solution, straining the dye solutions (a coffee filter works well) and then putting the eggs back in the solution overnight. Coloring designs on the eggs with wax pencils or crayons before dyeing will leave parts uncolored, for a batik effect. Altering the acidity of the dye solution may change the results. Students may even want to see if they get the same or different results in a basic solution (add sodium carbonate). g. Some follow-up investigations: Students can try using the dyes to color different materials such as various types of fabrics (cotton, nylon) or even paper. Students may want to attempt to color-match an artificially dyed food, such as macaroni and cheese or yogurt. Students can research products that are available here and in the U.K. to investigate what dyes are used in similar products. The U.K. has stopped using a number of these synthetic dyes in foods. 8. After students have finished their investigations, they may present their findings to their classmates and compare their results with those of their classmates. Additional Resources: http://www.flinnsci.com/Sections/Safety/safety.asp http://www.straw.com/sig/dyehist.html http://chemistry.about.com/od/holidayhowtos/a/eastereggdyes.htm http://www.chm.bris.ac.uk/webprojects2002/price/contents.htm Dye Chemistry (Middle School Level) 3 http://en.wikibooks.org/wiki/A-level_Applied_Science/Colour_Chemistry/Dyes http://www.pburch.net/dyeing/chemistry_reactivedyes_lesson.shtml http://www.newsday.com/opinion/oped/opinion-danger-of-artificial-food-dyes1.2787500 Dye Chemistry (Middle School Level) 4 Natural Dye Sources Color Ingredients Lavender Small quantity of purple grape juice Violet blossoms plus 2 tsp lemon juice Red Zinger tea Violet Blue Violet blossoms Hibiscus tea Red wine Blue Canned blueberries Red cabbage leaves (boiled) Purple grape juice Green Spinach leaves (boiled) Yellow Orange or lemon peels (boiled) Carrot tops (boiled) Celery seed (boiled) Ground cumin (boiled) Ground turmeric (boiled) Chamomile tea Green tea Brown Strong coffee Instant coffee Black walnut shells (boiled) Black tea Orange Yellow onion skins (boiled) Cooked carrots Chili powder Paprika Pink Beets Cranberries or juice Raspberries Red grape juice Juice from pickled beets Red Canned cherries with juice Pomegranate juice Raspberries Dye Chemistry (Middle School Level) 5 Student Worksheet Dye Chemistry Experiment Title: _____________________________Date: __________Name: _____________ Student Hypothesis or Question: ______________________________________________________________________________ Materials: Safety goggles Water __________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ Safety Precautions: ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ Procedure: Wear Safety Goggles for all lab work. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ Dye Chemistry (Middle School Level) 6 _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ Data and Observations: Dye Chemistry (Middle School Level) 7 Analysis of Data: _______________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ Conclusion: ___________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ Dye Chemistry (Middle School Level) 8