JCE Classroom Activity: #20

Cleaning Up with Chemistry: Investigatingthe Action of Zeolite in Laundry Detergentby the Journal’s Editorial Staff

BackgroundUntil 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 thisenvironmentally damaging effect and have replaced phosphates in most powdered laundry detergents. Several types ofzeolites 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). Thearrangement of the framework results in the formation of channels or pores within the zeolite. This porous nature allowszeolites to adsorb molecules and ions that are equal in size to or smaller than the pore openings, while excluding thosethat are larger (1). Sodium zeolite A softens water by exchanging the Na+ ions originally contained in its pores for theCa2+ and Mg2+ ions contained in hard water. A structural representation of zeolite A is on the student side of this activityand elsewhere in JCE (1–3).

Integrating the Activity into Your CurriculumThe 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 seenchemical 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 Detergents arean example of a chemical solution to an environmental problem: phosphates have been replaced by zeolites. In their roleas 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 includecatalysts for petroleum cracking, desiccants, and ion exchange materials.

About the ActivityThis 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 thecomparison 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 watersoftening (4). A zeolite model-building activity is also available (5).

Answers to Questions1. 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 precipitateswith soap.

2. The test tube that contains sodium zeolite A should have a higher level of suds. The zeolite softens the water byexchanging 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 absorbwater, affecting its mass.

4. Incomplete soil removal is common in hard water. The water-softening action of sodium zeolite A aids in soilremoval. If washed in hard water, white fabrics may become grayed and dingy. As unremoved soil deposits accumu-late, 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) thezeolite 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 Demonstrations1. Coker, E. N.; Davis, P. J.; Kerkstra, A.; van Bekkum, H. J. Chem. Educ. 1999, 76, 1417–1419.2. Smoot, A. L.; Lindquist, D. A. J. Chem. Educ. 1997, 74, 569–570.3. J. Chem. Educ. 1997, 74 (5), cover.4. Ceretti, H.; Hughes, E. A.; Zalts, A. J. Chem. Educ. 1999, 76, 1420–1421.5. Huang, Y. J. Chem. Educ. 1980, 57, 112–113.

perf

orat

edfo

ld h

ere

and

tear

out

Instructor Side

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: Investigatingthe Action of Zeolite in Laundry Detergentby the Journal’s Editorial Staff

This Activity Sheet may be reproduced for use in the subscriber’s classroom.

Did you ever read the list of ingredients on a box of powdered laundry detergent? Probably not. Do you know whatall the chemicals in the detergent do? Do you know how they help to get your clothes fresh and clean? In this activity, youwill investigate the properties of one ingredient, aluminosilicate. The particular aluminosilicate used in powdered laundrydetergent is sodium zeolite A. The structure below shows its framework. The holes or pores you see in the structure initiallycontain 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.

Try ThisYou 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 dishwashingsoap, 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 zeolitedoes 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 theheights 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.htmlWater 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

Most powdered laundry detergentslike the product shown on the leftlist aluminosilicate as an ingredient.

The structure of sodium zeolite A,an aluminosilicate, is shown on theright. Note the holes in the cage-like structure. These holes cancontain ions, such as Na+.

1416B Journal of Chemical Education • Vol. 76 No. 10 October 1999 • JChemEd.chem.wisc.edu