The Chemistry of Cat Litter: Activities for High School Students ToEvaluate a Commercial Product’s Properties and Claims Using theTools of ChemistryTeresa Celestino*,†,‡ and Fabio Marchetti*,†

†Chemistry Section, School of Science and Technology, University of Camerino, Via S. Agostino 1, 62032 Camerino, Macerata, Italy‡Technical High School “Galilei-Sani”, Via Ponchielli snc, 04100 Latina, Italy

*S Supporting Information

ABSTRACT: Educating future scientists and citizens is more effective if studentsare guided to correctly apply what they learned in school to their daily lives. Thisexperience-based work is focused on the study of a well-known commercialproduct: cat litter. This material offers different starting points for a criticalexamination. Questions related to physical properties at the origin of the litter’sefficacy, to information on chemical composition provided in the packaging, andto environmental features and possible noxiousness of cat litter were asked to beinvestigated by secondary school 14−15 year old students, through laboratoryexperiments based on problem solving approach, analysis of tag claims ofdifferent cat litter brands and cooperative learning activities. This multi-disciplinary approach gives the chance to learn effectively chemistry coreconcepts and to avoid the typical students’ lack of attention.

KEYWORDS: High School/Introductory Chemistry, Laboratory Instruction, Inquiry-Based/Discovery Learning,Problem Solving/Decision Making, Consumer Chemistry

■ INTRODUCTION

Chemistry teaching does not usually focus on the interplay ofscience, technology, and society, despite that this kind ofapproach has been very effective in education research carriedout in Italy1 and abroad.2 The Italian school curriculumincludes these topics,3 but teaching practice in them is notmuch developed.The perception of chemistry relevance in everyday

applications enables students to go beyond the surface featuresof phenomena, and learning of chemistry key concepts can bemore effective.4 An approach centered on real world problemscan help to counteract the typical lack of attention character-izing 14−15 year old students.5 The present study focuses on ateaching sequence of didactic activities centered on questionsrelated to cat litter, and learning outcomes of chemistry coreconcepts are compared with those of students not involved inthe project. The teaching sequence was carried out during the2012−2013 and 2013−2014 school years, with four classes of14−15 year old students of a technical high school in Italy, for atotal of 74 students.

■ CHEMISTRY BACKGROUND: CAT LITTERFORMULATIONS

Cat litter is a well-known product. It is a cheap material,existing in a wide variety of types, largely available and safe inorder to perform simple experimental tests. Cat litter’s mostcommon material is clay, although silica-based “crystal” variants

and recycled paper “pellets” are also used. The biochemistThomas Nelson observed that a certain type of clay clumped upin the presence of moisture, so he developed the clumping litterin 1984.6 Clumping/not clumping clay cat litters are naturalproducts. Nevertheless, silica particles found in clay cat littersare known to be carcinogenic.7

Moreover, environmental impact in using commercial catlitter has become a matter of concern: clay litter is commonlyproduced in an environmentally degrading process using stripmining. Some pet owners prefer the environmentally friendlybiodegradable litters, made from various plant resources. Thistype of litter does not contain carcinogenic silica dust. Silica gellitter, often referred to as “crystal litter”, is a porous granularform of silicon dioxide dotted with tiny pores, allowing crystalsto absorb cat urine and allowing the water to evaporate off.Many types of cat litters are for sale, so quite often people are

undecided about the right choice. Most people usually decideon price criteria; others take into consideration the need ofreducing smell or are concerned about disposal of clay withadsorbed urine. Rarely, people buy cat litters exclusively on thebasis of environmental criteria.

■ LESSON PLAN

The teaching sequence starts with four questions asked to thestudents:

Published: May 5, 2015

Activity

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© 2015 American Chemical Society andDivision of Chemical Education, Inc. 1359 DOI: 10.1021/ed500505j

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1. How can the physical properties at the origin of thelitter’s efficacy be evaluated? How much does the methodof extracting or synthesizing cat litter influence cost?

2. What information does the packaging provide about

composition? Can we carry out chemical tests?3. How can the product’s sustainability be proved? Can we

plan experiments to evaluate the product’s rate ofdecomposition?

4. Why do some scientific articles deal with possible cat

litter noxiousness?

At the beginning, the teacher leads students in analyzing sixproduct samples (Figure 1). Then, the teacher plans researchand laboratory activities in order to answer previous questions.The didactic sequence is structured in four sections (sections

1−4), each corresponding to one of the questions above; eachsection is organized into three phases:

• Phase I: Critical approach to the proposed issue. Theteacher introduces the issue and assigns related home-work.

• Phase II: Laboratory experiments/analysis of documentsin order to answer the question. This is the central part

Figure 1. Product samples examined: (a) clumping/nonclumping clay litters; (b) biodegradable litters (with and without yeasts); (c) silica gel litters.

Table 1. Chemistry Content Involved in Sections 1−4 of This Activity

Student Activities First-Year High School Chemistry Syllabus Contents

Section 1Organoleptic characteristics (dry and wetsample) analysis

Differences between homogeneous and heterogeneous materials; insoluble aggregates and heterogeneous mixtures

Liquid or gas absorption capacity evaluation Liquid/solid, gas/solid, liquid/gas mixtures; solutions, colloids, coarse dispersions; intensive and extensiveproperties

Density measurement Basic and derived units; errors and uncertainty in experimental data; absolute and relative errors; systematic andrandom errors; precision and accuracy; rounding off/up experimental data; significant digits in addition,subtraction, multiplication, and division operations

Section 2Critical analysis of tags’ claims of commercial catlitters

Percentage concentrations in solid mixtures; solid particle dimensions

Solubility evaluation; solid−liquid extraction;Paper/thin layer chromatography

Separation techniques

Flame test; Borax bead test Macroscopic metal properties referring to the periodic table; chemical transformationsSection 3

Critical analysis of tags’ claims of commercial catlitters; research about some compounds(origin, costs, safety)

Information about safety of chemicals; differences between natural and synthetic compounds

Theory on composting process (under differenttemperature, humidity, or sunlight conditions)

Differences between physical and chemical transformations; chemical transformations

Section 4Research about particulate matter dangers Suspended solid particles in the atmosphere; chemicals’ safety and health protection issuesReading of simplified research papers;discussion/expression of critical points of view

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of the work, carried out by cooperative learning instudents’ groups.

• Phase III: Global examination of the accomplished workto develop metacognitive skills. Students try to answerquestions related to phase I. This phase is also centeredon cooperative learning strategies.

Table 1 describes a synthetic overview of issues involved ineach section, with the corresponding chemistry contents andteaching strategies. The learning activities are listed in Table 2.Section 1, Question 1: Chemical Properties

For this section 6 h of class time is required. The students’worksheets 1−4 in the Supporting Information describe indetail the activities carried out. They are aimed at developingthe students’ skills in analyzing different systems of matter andevaluating some physical features, such as the density and theadsorption ability of cat litters.Phase I. Students are asked to observe and describe six

samples of cat litters. Each tag is analyzed by the students andcompared with the others.Phase II. Different samples of cat litters are assigned to

students’ groups, and they communicate to each other theirremarks and final results. After the organoleptic featureevaluation of dry and wet samples, students measure thedensity through the water displacement method,8 evaluating/calculating experimental errors, as described in the textbook.9

Additionally, they evaluate some litters’ properties such asliquid or gas absorption ability.Phase III. Students reflect upon the examined properties of

products, relating them with the quality/price ratio.Section 2, Question 2: Chemical Composition

For this section 12 h of class time is required. The students’worksheets 5−18 in the Supporting Information describe indetail the activities carried out. This section deals with theorigin of dye of some colored (blue and pink) grains in twodifferent brands of silica gel litters10 (see Figure 1c). In bothcases, the nature of the dye is not specified on the packages.However, the one containing blue granules is tagged 100%natural product and it can be used in composting. Furthermore,the package claims that the blue crystals possess antibacterialproperties.Phase Ia. Students are guided in formulating some

hypotheses, helped by some very simple experimental tests(as flame test11 and Borax bead test12). The teacher suggeststhat a skilled chemist should associate the blue color to a cobaltcompound, usually employed as humidity indicator. Never-theless, the insolubility of colored grains in both water andconcentrated acidic solutions under heating prevents the

execution of chemical tests to confirm the presence of somecobalt compound. This evidence suggests that the dye isprobably embedded in a glass structure. The teacher thensuggests that students should send an e-mail to manufacturersof silica gel litters containing blue or pink grains, in order to getmore details about the nature of the dye and the origin ofclaimed bacteriostatic activity.

Phase IIa. The flame and Borax bead tests give negativeresults.

Phase IIIa. Students’ groups are asked to elaborate someconclusions about the presence of metals in the analyzedsamples.

Phase Ib. Only two companies replied by e-mail to students’inquiries. The company producing silica gel cat litter with pinkgrains answered: “the dye is allowed by the European Union”,without specifying its chemical nature. According to claims ofthe company producing silica gel cat litter with blue grains, thecoloring agent is based on anthocyanins and its function is justaesthetics, denying the bacteriostatic function reported on thetag. A document about anthocyanins is given to students, andthey are asked to propose a suitable separation method foranthocyanins’ detection, among techniques already studied inprevious lessons.

Phase IIb. Once solubility test13 results are obtained, thinlayer chromatography and paper chromatography14 are carriedout by using the alcoholic extract from the blue/pink samples.Figure 2 shows the experimental steps aimed at verifying theanthocyanin content in the colored silica gel grains. Only therate of migration of blue extract was different from that of theother samples; therefore, anthocyanins are not present in theblue extract (Figure 3). Also the laboratory test carried out on

Table 2. Phases and Activities Involved in Each Section of the Teaching Sequence

Activities

Question Phase I Phase II Phase IIIHours

Required

1 Sample observation and analysis of tags’ claims Laboratory measurementsand experimental data in-terpretation

Laboratory reports and questionnaire (in order tocompare different products’ properties)

6

2 Sample observation and analysis of tags’ claims; inquiry aboutchemical composition (by information request writing, readingdocuments, Web research)

Chemical analysis and ex-perimental data interpre-tation

Laboratory reports and questionnaire and struc-tured exercises (to develop a critical overview ontags’ claims provided)

12

3 Tag claim analysis and reading documents Experimental path planningon cat litter digestion bycomposting

Product’s schedule planning to be realized (sixmonths required to collect data to put in theschedule)

4

4 Reading documents and discussion Text comprehension exer-cises

Composition and structured exercises (to develop aglobal understanding of the subject)

4

Figure 2. Experimental sequence to verify the anthocyanin presence inthe silica gel litters with blue and pink grains.

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pink extract (possible color change depending on pHvariation15) was negative.Phase IIIb. Assuming a correct execution of chemical tests,

false information has been provided by cat litter producingcompany.

Section 3, Question 3: Product Decomposition

For this section 4 h of class time is required. The students’worksheets 19−21 in the Supporting Information describe indetail the activities carried out. For each analyzed cat litter,students are asked to organize a schedule containinginformation on the chemical composition and its compostingprocedure.Phase I. Some silica gel litters are described as environ-

mentally friendly products, since they will “turn out into sand”because of their “digestive process in 4−6 months by light andwater action”. In order to verify the exactness of thisinformation, the teacher assigns homework based on readinga document about the composting process.16

Phase II. During this phase each students’ group is asked toplan laboratory experiences under the teacher’s supervision, onthe basis of contents learned in the previous phase. At the end,all planned experiences are merged into a single collectiveexperimental proposal.Phase III. Students plan the structure of a hypothetical

schedule, exactly specifying the chemical composition of anylitter and describing the way of composting in a concise,complete, rigorous, and understandable form.

Section 4, Question 4: Particulate Matter Research

For this section 6 h of class time is required. The students’worksheets 22−24 in the Supporting Information describe indetail the activities carried out. The section is devoted todevelop students’ abilities in searching information on ascientific issue and comparing research reports.Phase I. Two simplified research reports17,18 about cat

litter’s noxiousness, caused by particulate matter emission,19 aregiven to students to provide them with some examples ofexperimental methods used in research laboratories.Phase II. After analyzing each case study, students achieve

some learning outcomes such as texts’ comprehension andsubject knowledge. In detail, they acquire knowledge aboutparticulate matter characteristics, origin, and possible health

dangerous effects. Sentence completion exercises and multiplechoice tests are assigned to the students.

Phase III. Students list the main differences between the tworesearch reports and choose which appears more reliable. Ofcourse, this part needs a specific support by the teacher.

■ FINAL RESULTS

The outcomes of this teaching sequence are essentiallyqualitative data because of the limited number of studentsinvolved. Nevertheless, they suggest a certain efficacy. Studentsappreciated the activities proposed, in particular the laboratorywork. A student stated, “Chemistry is not so boring as I’ve beenthinking for a long time: we can use many daily life products tounderstand it. Our teacher raised enthusiasm in us, especiallywhen we discovered that the company very probably lies ondye’s chemical composition.” Another student seemed fullysatisfied: “Finally I can manage with relative and absoluteerrors, or with the procedure to calculate the error related to aquantity (such as density) obtained by the division of two otherquantities. It was funny to understand all that stuff byexperiments on a cat litter!” Concerning the experimentalactivities, a student affirmed: “I liked very much thechromatography experiment: although we have not discoveredthe nature of the dye, we were able to exclude a hypothesis.” Astudent admitted: “When the teacher asked us to study samplesof different cat litters, I started to laugh. I thought it was a notsuitable material for school work. But now I know that I canlearn a lot from everything: each object hides secrets.” Studentswere mainly surprised by the falsity and/or incompleteness ofpublicity information by companies of cat litters: “They statedby e-mail that colored granules have an aesthetic function only.So, why did they write on the package their function isantibacterial? Aren’t they afraid of the consequences?” and“Why did they answer the dye is authorized by the EuropeanUnion without specifying its chemical composition? Why aresilica gel litters produced in China? Answering all thesequestions need a lot of time in gathering information. I realizedthat any product we use brings with it very complex issues.”The final test on some chemistry contents showed that the

outcomes of classes working on the project were considerablyhigher than those of the control group. Language, criticalthinking, problem solving, and analysis skill development of the

Figure 3. TLC samples, from left to right: (a) alcohol extracts of red chicory, red turnip, bilberry, blue silica gel crystals; (b) alcohol extracts of redchicory, red turnip, bilberry, pink silica gel crystals.

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students involved in the project were also assessed by theevaluation of worksheets filled during the school year.To answer in a definite and complete way the complex

questions posed is of course not possible, especially in a schoollaboratory. Anyway, the main expected outcome was related tothe inquiry students’ skill development in order to formulate amore mature vision of chemistry and its relationships witheveryday life, global problems, and ethical issues.

■ CONCLUSIONSWe have designed a novel didactic activity centered on thestudy of cat litter, a largely available and safe commercialproduct existing in a variety of types. Then we have run thedidactic sequence with Italian secondary school students of 14−15 years old. They were asked to investigate some questions onthis product (physical properties at the origin of the litter’sefficacy, information on chemical composition provided in thepackaging, product’s sustainability and possible noxiousness) byproblem solving based laboratory experiments, analysis ofvarious documents, and cooperative learning activities. Withinthis multidisciplinary approach, in a stimulating educationalcontext, students were strongly encouraged to think and learnactively several core concepts of chemistry.

■ ASSOCIATED CONTENT*S Supporting Information

Students’ worksheets including hazards. This material isavailable via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Authors

*E-mail: teresa.celestino1@istruzione.it.*E-mail: fabio.marchetti@unicam.it.Notes

The authors declare no competing financial interest.

■ ACKNOWLEDGMENTSUniversity of Camerino and Technical High School “Galilei-Sani” are gratefully acknowledged.

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