The Use of Real Life Samples for Unknowns in Analytical Chemistry

Anne T. Shemen North Central College, Naperville. IL 60566

Analvtical chemistry courses often include synthetic, commewial namples orunknowns for student analysis. Such synthetic samples are used for qualitative and/or quantita- tive analysis "nknowns. In quantitative analysis courses the student is expected to determine one or more of the compo- nents within a few parts per thousand accuracy and preci- sion. These samples are valid for developing a student's laboratorv techniaue. but the exclusive use of synthetic sam- ples a sterile view of chemical analysis. In addition to the comoonents to be deterted and/or determined, these unknowns'often contain only inert materials. The use of such samples often neglects the problems of proper sampling procedures and techniques as well as sample pretreatment (including removal of interfering elements) and matrix ef- fects. An alternative to the use of the synthetic unknowns is the use of real-life suhstances, which may increase interest and variety (13). When an unknown is required for an experiment and a real life unknown is suitable, I will then search in the Journal of Chemical Education, laboratory texts, textbooks, and analytical hooks that are for special substances, i.e., for the analysis of water, or other materials.

How I Use Real Llfe Samples in the Currlculum

The Regular Experiment with Complete Directions In this type of experiment there are regular directions for

the analysis, and the student performs the experiment as written. The only difference is that the sample is obtained from the reallife sources. The use of a sample that is familiar to the student does spark interest and gives variety. The students tend to expect only sterile synthetic samples. The students enjoy comparing their results with the published or printed results.

The Independent Project with Specific Guidelines The independent project has additional benefits and add-

edrisks. The initial directions must state the guidelines. The instructor must also be prepared to supply guidance and firmness. The advanages of independent projects have been cited by a number of authors including Roscher (41, Hicks (5), and Bramstedt (6).

Examples of Where I Use Real Llfe Samples In the Currlculum

General Chemistry In our introductory titration laboratory we use vinegar as

a class unknown. The students will standardize their base, and then samples of the commercial vinegar are titrated. Students like the idea of being able to compare their answer with the answer that is on the label.

Qoantltative Analysls In the quantitative analysis course I use two real life sam-

ples. The first real life experiment is a regular experiment where the students determine the neutralizing power of ant- acid tablets. The experiment has several variables in that I have about six different hrands of antacid tablets. These

tablets vary in their soluhility in 0.1 M HC1. The big problem is with the filler. Some of the filler is insoluble hut adsorbs the indicator on the surface. This must be removed by filtra- tion before a satisfactory end point can be determined. Tums is verv had in this resoect. - -

The second real life experiment is an independent project. This project is the determination of one component of a real life substance. The student must choose the analyte, supply the analvtical method and provide the sample to be ana- lyzed. he types of samples that my students have deter- mined include water, foods, vitamin supplements, soaps, bones, tobacco, ~ ~ l e k o l , tea, coffee, sod< gasoline, coins, and body fluids. The students have frequently determined the amountsof iron, vitamin C, fat content, phosphate, calci- um, caffeine, chlorine, and copper in real life samples. The determination of iron, calcium, and chloride are always pop- ular. I learn as I have my students do their real life projects. The following are actual quotes from students after they finished the real life project in quantitative analysis: "The analysis relates to every day areas." "Chemistry is not just in the textbook, it is everyday life." "The real life helped to develop my self-confidence. I had to figure it out by myself." "It was not a regular procedure, I was able to participate in nlannine the exoeriment." "I learned that what was printed hoes n ~ ~ a l w a ~ s ~ w o r k . ' ~ "I had to try several things a i d when it worked I felt a sense of accomplishment."

Instrumental Analvsls In the instrumental analysis lahoratory we routinely add a

real life unknown as the final experiment for each instru- ment. The real life determinations are used as unknowns after the student has mastered the operation of the given instrument. There will often he a synthetic unknown before the student is given the real life sample for analysis. The real life sample may require the use of the analytical spike or the method of standard addition. For the atomic absorption the students will take a few Cherrios to determine the iron or copper content. We are considering the inclusion of methods to determine some of the metals in brass fittings by two . instrumental methods.

Independent Study Projects Some students eniov the analvsis of the real life samples . .

and request to do additional fndependent work on sub- stances. This is esoeciallv true if there is a special interest in a given type of compound. When this is undertaken, method develooment and comparison is encouraged. Also more ex- tensive literature workis required. 1nteriting projects have heen done on isolation and determination of iron in hreak- fast foods.

Advantages of Uslng Real Llfe Substances lor Analysis The use of the real life substance for analytical samples

increases the level of student interest and adds varietv to the ~~~~

course. The use of the real life sample helps the student to relate chemistry to everyday life. Many real life samples facilitate the consideration of sampling techniques. The use

598 Journal of Chemical Education

of the real life substance can serve as an introduction to the area of choice of analvtical method and analytical method development. If the real life sample is presented in a project- type experiment, then there are additional advantages. The total analytical process (from problem definition to commu- nication of results) can be experienced by the student. The student must make choices a t many stages in the project. Each of these choices increases the students level of respon- sibility for the project.

Problems of Using Real Llfe Samples for Analysis In the use of the real life sample the instructor must be

prepared to deal with certain problems. The problem of matrix effects is often encountered and must he solved. Interferences are often present and not anticipated by the student or the instruct^^. Dissolving thesample is often a big vroblem. If the instructor makes the real life sample a pro- ject for the student and the student also chooses and devel- ops the analytical method, a variety of chemicals must be nvailahle. When real life samvles are used as unknowns in .. - ~ ~ - ~ ~ ~ ~ ~

regular determinations, the instructor is faced with the nroblem of knowine the "actual content" of the analvte in ;he real life suhsta&e. Jones (7) suggests the methods of standard addition and doing "check samples" to insure the analytical accuracy. The check sample illustrates the prac- tice which should be standard procedure in any "real" ana- lytical chemistry laboratory.

Level of Creatlvlty Expected of the Students In the regular experiments with real life unknowns the

student is not expected to exercise more creativity than one would exercise with a synthetic unknown. Often there are problems of inert materials that are insoluble or other fac- tors that one must address. In the real life projects the

students can be expected to do any or all of the following: take an idea, locate a method, adapt the method to our situation, and perform the experiment. Students can also be expected to devise creative ways to show that they do indeed understand the meaning of a good analytical sample and how good analytical samples are obtained. Students can also be expected to show creativity in dealing with the problems encountered in the various steps of the analysis.

Conclusion I have found that the use of the real life sample has in-

creased student interest, student curiosity, and the meaning of analytical chemistry. We are limited in the use only by our own creativity and imagination. I feel that the advantages are far greater than the prohlems. I would encourage any instructor to try to add a certain percentage of real life samnles to his or her analvtical chemistrv courses. The extra effoit is rewarded with much satisfaction and student inter- est. The reallife project permits me to introduce the element of analytical research in my quantitative analysis course. I have found that the students do see a vurpose to analvtical chemistry. Some of my students have cbnsidered i t as a career and are practicing analytical chemists today.

Literature Clted I. CummilteeReport. J. Chem.Educ. 1974,51,472-473. 2. Cnrwin. J. F. J. Chom.Educ. 1971,48,522-523. 3. Buono.J. A.; Faschin~, J. L. J. Chem.Educ. 1973.50,616617. 4. Ro8cher.N. M. J. CdSci. Teach. 1973.213).33-34. 5 . Hick8.D. G. J.Col. Sri. Teach. 1973.2 14). 27-29. 6. Bramafcdt, W.; Korfmseher, A,: Laylaff, T. J. Cham. Edue. 1973.50.252-25s 7. Jones. B.E. J.Chem.Educ. 1973.60.822.

Resent64 at the 200th American Chemical Society National Meet- ing in Washington, DC. August 30, 1990.

Volume 68 Number 7 July 1991 599