Instructor Information
JCE Classroom Activity: #48
Through the Looking Glass In this Activity, students compare several different window cleaner recipes to determine the purpose each ingredient in a window cleaner serves. They then develop their own “New and Improved” recipe and test its performance against commercial window cleaner.
Typically three or four items are listed as ingredients on a container of window cleaner: water, isopropyl alcohol, ammonia, and coloring agent. Water serves as a solvent and is used to dissolve some of the dirt. Isopropyl alcohol serves as a wetting agent; it prevents water from beading up and aids in evaporation of the cleaner. Ammonia is a good grease cutter (1) because of a hydrolysis reaction between ammonia and fats. Triglyceride (a component of grease), water, and ammonia react to produce glycerol and ammonium salts of fatty acids, which are water soluble (2). Vinegar also functions well as a grease cutter, causing a similar hydrolysis. However, more cleaners use ammonia because it costs less than vinegar.
Integrating the Activity into Your Curriculum This Activity complements the National Chemistry Week 2002 theme “Chemistry Keeps Us Clean”. It could be used as a follow-up Activity for NCW. It ties in with consumer chemistry. Instructors could also discuss the hydrolysis reaction between ammonia and a fat that allows ammonia to work well as a grease cutter. Interdisciplinary extensions for art, business, and language arts classes could be to develop a marketing campaign for a window cleaner, including written advertisements, videotaped commercials, and container designs. photos by J. J. Jacobsen and N. S. Gettys
About the Activity
perforated
This Activity is based on an article published previously in the Journal, “Creating a Window Cleaner Company” (1). The original article’s authors also included a similar experiment in the book Dirt Alert—The Chemistry of Cleaning (2). Goggles must be worn during this Activity because ammonia is used. Students are told in the Student Activity not to make any cleaning solution that contains more than 20% ammonia by volume and not to include any additional ingredients other than water and isopropyl alcohol. This should be emphasized, especially since students will be developing their own window cleaner recipe toward the end of the Activity. Students will make 50 mL of each window cleaner recipe. Small spray bottles (six ounces or smaller) should be used because the liquid level in larger bottles will usually not be high enough to allow the liquid to be effectively brought up the inside tube. Use spray bottles that produce a mist, rather than a stream. Either pump- or trigger-style spray bottles work well. Discount stores commonly carry these bottles in the health and beauty section, along with mirrors, which can be used to test the window cleaner solutions.
Answers to Questions 1. 2.
3. 4.
Top: Commercial window cleaners usually contain water, isopropyl alcohol, and ammonia. Bottom: A fingerprint is made on a mirror that has been divided into sections with pieces of masking tape.
See background section above. Each recipe left out one of the ingredients. Recipe B did not contain ammonia, recipe C did not contain isopropyl alcohol, recipe D did not contain added water (note that the rubbing alcohol and ammonia solutions both contain water, so it is not possible to make a cleaner without water using these ingredients). Comparing cleaners allows one to see the result of not having a key ingredient. Water is the least expensive ingredient and works well as a solvent. The cost of commercial window cleaner will usually be much more than the cost of equivalent amounts of water, isopropyl alcohol, and ammonia solution. Prices will vary depending on the brand of each item and where it was purchased. Commercial cleaners often also contain coloring agents and fragrances, which add to the cost of the product. Companies that sell window cleaner must pay production, packaging, and advertising costs. In order to make a profit, they must sell their product for more than their total expenses.
References 1. 2.
Sarquis, A. M.; Peters, Bruce L. Jr.; Coffey, Linda W.; Hershberger, James; Bucheit, Rex. Creating a Window Cleaner Company. J. Chem. Educ. 1995, 72, 344. Sarquis, Mickey, Ed. Dirt Alert—The Chemistry of Cleaning; Terrific Science Press: Middletown, OH, 1999. JCE Classroom Activities are edited by Nancy S. Gettys and Erica K. Jacobsen
JChemEd.chem.wisc.edu • Vol. 79 No. 11 November 2002 • Journal of Chemical Education
1360A
This Classroom Activity may be reproduced for use in the subscriber’s classroom.
fold here and tear out
Background
JCE Classroom Activity: #48
Student Activity
Through the Looking Glass “Extra cleaning power!” “Get your windows sparkling clean!” “Now contains ammonia!” “Now with vinegar!” “Now with…” What? Most of us are familiar with commercial window cleaners and advertisements that persuade us to buy them. A look at the ingredients on the product label usually yields two items: water and isopropyl alcohol. Many window cleaners also contain ammonia. What do these ingredients do? Is it possible to make a window cleaning solution on your own that will get your windows just as clean? In this Activity, you will prepare window cleaner using several recipes and investigate what each of the ingredients does. Then you can design and mix up your own batch of “New and Improved Window Cleaner” and test it to see how it compares to a commercial product.
Try This
Be Safe! Goggles must be worn dur-
ing this Activity. Do not inhale ammoYou will need: a mirror (15 × 15 cm or larger), masking tape and a permanent marker, materials to make the mirror dirty (soil, dust, oil, etc.), five small (six ounce or nia vapors. Do not mix any cleaning smaller) spray bottles, water, 70% isopropyl alcohol (rubbing alcohol), household solution that contains more than 20% ammonia solution (not sudsy ammonia), measuring spoons or a graduated cylinder, ammonia solution by volume. Do not plastic cup or beaker, spoon, funnel, paper towels, and commercial window cleaner. spray the cleaning solutions at your__1. Mark a clean mirror into four equal sections using pieces of masking tape. Label self or anyone else. the sections A–D, writing the labels on the tape with a marker. __2. Get each of the sections equally dirty by wiping your forehead or the side of your nose with a finger and placing two fingerprints in each section (if you cannot see the fingerprints rub a tiny drop of vegetable oil between your fingers and then make fingerprints); then wipe a very small quantity of soil or dust mixed with a drop of water in each section, but not on top of the fingerprints. Set the mirror aside. __3. Label four small spray bottles A–D. Each section of this mirror contains two __4. Prepare four different window cleaners using the recipes in the table. Measure all fingerprints and a smear of dirt mixed ingredients for a recipe into a plastic cup or beaker and mix thoroughly with a with water. spoon. Then transfer the liquid into its labeled spray Recipe A Recipe B Recipe C Recipe D bottle through a funnel. Rinse the cup and funnel thoroughly with water and proceed with the next recipe. water 25 mL 25 mL 40 mL (15 mL = 1 tablespoon; 5 mL = 1 teaspoon) 70% isopropyl alcohol 20 mL 25 mL 40 mL __5. Pump the sprayer for bottle A into a paper towel a few times until the cleaner flows out easily; then place the ammonia solution 5 mL 10 mL 10 mL paper towel into a trash container. Place the mirror from step 2 on a flat, horizontal surface. Spray section A of the mirror with one spray from bottle A, being careful not to let the spray get into the other sections. With a clean paper towel, wipe section A with four downward strokes covering the entire section and using moderate pressure. Record your observations. __6. Repeat step 5 for each of the three remaining bottles of cleaner and mirror sections. Be sure to use a fresh paper towel for each window cleaner. __7. After approximately five minutes, examine and compare the mirror sections. Record your observations. __8. Using only the three ingredients listed in the table, create your own recipe for a “New and Improved Window Cleaner”. It should not contain more than 20% ammonia solution by volume (10 mL in a total volume of 50 mL). Mix up your recipe and transfer it into a clean, labeled spray bottle. Compare the cleaning ability of your solution with that of commercial window cleaner, using the same testing procedure described in steps 2 and 5.
Questions __1. __2. __3. __4.
What purpose does each of the three ingredients serve in the window cleaner? How did recipes B, C, and D allow you to determine the purpose each ingredient serves in the window cleaner? Why is water the main ingredient in most window cleaners? Estimate the cost of your homemade window cleaner and compare it with the price of commercial window cleaners. Why does commercial window cleaner cost more than the total cost of its ingredients?
Information from the World Wide Web (accessed September 2002) 1. 2. 3.
Window Cleaning Solution–Ask a Scientist. http://newton.dep.anl.gov/askasci/chem99/chem99271.htm Clorox Labs: Packaging and Shipping. http://www.clorox.com/science/labs/packaging_lab.html Chemical of the Week: Ammonia. http://scifun.chem.wisc.edu/chemweek/ammonia/ammonia.html This Classroom Activity may be reproduced for use in the subscriber’s classroom.
1360B
Journal of Chemical Education • Vol. 79 No. 11 November 2002 • JChemEd.chem.wisc.edu
