Instructor Side
JCE Classroom Activity: #20
Cleaning Up with Chemistry: Investigating the Action of Zeolite in Laundry Detergent by the Journal’s Editorial Staff
fold here and tear out
Background Until recently, sodium tripolyphosphate was used in powdered laundry detergent to serve as a builder and soften the laundry water. However, phosphates in wastewater run-off stimulate algal growth. Zeolites soften water without this environmentally damaging effect and have replaced phosphates in most powdered laundry detergents. Several types of zeolites exist, with characteristic pore sizes. Sodium zeolite A is the one most commonly used in powdered detergents. The framework of a zeolite structure is formed by linking tetrahedral SiO4 and AlO4 units at their corners (1). The arrangement of the framework results in the formation of channels or pores within the zeolite. This porous nature allows zeolites to adsorb molecules and ions that are equal in size to or smaller than the pore openings, while excluding those that are larger (1). Sodium zeolite A softens water by exchanging the Na+ ions originally contained in its pores for the Ca2+ and Mg2+ ions contained in hard water. A structural representation of zeolite A is on the student side of this activity and elsewhere in JCE (1–3).
Integrating the Activity into Your Curriculum The investigation of zeolites in powdered laundry detergent brings a real-world, practical aspect to the classroom. It helps students to apply their chemical knowledge to the realm of consumer products. Students have undoubtedly seen chemical names that they know nothing about on product labels. This activity demystifies a chemical in one product. The activity can also be used as a lead-in for a discussion of environmental issues and water chemistry. Detergents are an example of a chemical solution to an environmental problem: phosphates have been replaced by zeolites. In their role as water softeners, zeolites also serve as an example of a cation exchange material. Zeolites are used in many other areas and can be incorporated into a discussion of industrial chemistry. Uses include catalysts for petroleum cracking, desiccants, and ion exchange materials.
perforated
About the Activity This activity is adapted from a series of experiments with zeolites previously published in JCE (2). In this activity, students extract sodium zeolite A from powdered laundry detergent and examine its properties. For the detergent samples, students must use a powdered laundry detergent that contains aluminosilicate. You may wish to have students bring detergents from home. Small amounts of powdered detergents can be purchased at laundromats. Grocery stores also often sell powdered water softeners in the laundry aisle. A possible extension activity could be the comparison of the amount of zeolite in powdered water softener to the amount of zeolite in detergent. A more advanced zeolite experiment can be found in this issue of JCE (1), along with a related experiment on water softening (4). A zeolite model-building activity is also available (5).
Answers to Questions 1. Water essentially free of Ca2+ and Mg2+ is called soft; if appreciable concentrations of either or both are present, it is called hard. Ca2+ and Mg2+ form precipitates with soap, hindering suds formation. Na+ doesn’t form precipitates with soap. 2. The test tube that contains sodium zeolite A should have a higher level of suds. The zeolite softens the water by exchanging its Na+ ions for the Mg2+ and Ca2+ ions contained in hard water. This results in better sudsing action. 3. Hygroscopic materials absorb water from their environment. In a humid environment, the detergent would absorb water, affecting its mass. 4. Incomplete soil removal is common in hard water. The water-softening action of sodium zeolite A aids in soil removal. If washed in hard water, white fabrics may become grayed and dingy. As unremoved soil deposits accumulate, fabrics feel harsh and stiff. 5. Some hypotheses are (i) the zeolite remains on the clothing, (ii) the zeolite is deposited in the washing machine, (iii) the zeolite is washed away with the laundry water. Experiment descriptions will vary depending on the chosen hypothesis. 6. Zeolites are also used as catalysts for petroleum cracking, as desiccants, and as ion exchange materials.
Additional Activities and Demonstrations 1. 2. 3. 4. 5.
Coker, E. N.; Davis, P. J.; Kerkstra, A.; van Bekkum, H. J. Chem. Educ. 1999, 76, 1417–1419. Smoot, A. L.; Lindquist, D. A. J. Chem. Educ. 1997, 74, 569–570. J. Chem. Educ. 1997, 74 (5), cover. Ceretti, H.; Hughes, E. A.; Zalts, A. J. Chem. Educ. 1999, 76, 1420–1421. Huang, Y. J. Chem. Educ. 1980, 57, 112–113.
This Activity Sheet may be reproduced for use in the subscriber’s classroom. JChemEd.chem.wisc.edu • Vol. 76 No. 10 October 1999 • Journal of Chemical Education
1416A
JCE Classroom Activity: #20
Student Side
Cleaning Up with Chemistry: Investigating the Action of Zeolite in Laundry Detergent by the Journal’s Editorial Staff Did you ever read the list of ingredients on a box of powdered laundry detergent? Probably not. Do you know what all the chemicals in the detergent do? Do you know how they help to get your clothes fresh and clean? In this activity, you will investigate the properties of one ingredient, aluminosilicate. The particular aluminosilicate used in powdered laundry detergent is sodium zeolite A. The structure below shows its framework. The holes or pores you see in the structure initially contain sodium ions. These sodium ions can be exchanged for other ions. In this activity, you will extract sodium zeolite A from powdered laundry detergent and examine its properties. The structure of sodium zeolite A, an aluminosilicate, is shown on the right. Note the holes in the cagelike structure. These holes can contain ions, such as Na+. Most powdered laundry detergents like the product shown on the left list aluminosilicate as an ingredient.
Try This You will need powdered laundry detergent that contains aluminosilicate, a scale or measuring spoons, two 100-mL beakers, stirring rod, funnel, medium filter paper, two test tubes with stoppers, tap and distilled water, liquid dishwashing soap, and eyedropper. __1. Weigh 5–6 grams (about 1 tablespoon) of powdered laundry detergent. __2. Place 50 mL of distilled water in a 100-mL beaker. Add the detergent to the water and stir with a stirring rod for several minutes. (Some solid will remain. Sodium zeolite A is the only insoluble component of detergent.) __3. Fold a piece of filter paper as your instructor specifies and place it into a funnel. Filter the mixture from step 2 into a second 100-mL beaker. Describe what you see on the filter paper. The substance on the filter is sodium zeolite A. __4. After the solution has gone through the filter, take the filter paper out of the funnel and unfold it. __5. Fill two test tubes half-full of tap water. Place a very small drop of liquid dishwashing soap in each test tube using an eyedropper. Label the tubes 1 and 2. To tube 1, add half of the zeolite you extracted from the detergent. The zeolite does not need to be dried. __6. Stopper both test tubes. With one in each hand, simultaneously shake both test tubes 5 or 6 times. How do the heights of the two suds layers compare? __7. Optional: Repeat steps 5 and 6 with water from another source and the rest of the zeolite. Are the results the same?
Questions __1. The amount of suds formed by soap in water is related to the hardness of the water. Define the terms “hard water” and “soft water”. Give a chemical explanation of how hardness affects the formation of soap suds. __2. Was the hardness of the water changed by the addition of sodium zeolite A? What happens chemically to ions in water when zeolite is added? __3. Sodium zeolite A is hygroscopic. What does this term mean? Would this property affect your mass of detergent if you performed this activity in a humid environment? __4. How does the addition of sodium zeolite A improve powdered laundry detergent? What would your laundered clothes be like if the zeolite were not in powdered laundry detergent? __5. Form a hypothesis about what happens to sodium zeolite A at the end of the wash cycle. Describe an experiment you could do to test your hypothesis. __6. What are some other uses for zeolites?
Information from the World Wide Web
(all sites accessed August 1999)
Zeolite Questions and Answer Page. http://www.zeolyst.com/faq.html The Chemistry of Cleaning, Part I. http://www.optc.com/~btoback/detergent.html Water Quality and Laundry Problems. http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/tc1.html Laundry Balls and Laundry Discs. http://www.optc.com/~btoback/laundrystuff.html
This Activity Sheet may be reproduced for use in the subscriber’s classroom. 1416B
Journal of Chemical Education • Vol. 76 No. 10 October 1999 • JChemEd.chem.wisc.edu
