Larry D. Francis Universitv of Illinois Urbono, ~~ilnois 61801
II
Computer-Simulated Qualitative Inorganic Chemistry
A student performing an inorganic qualitative analysis lab has many demands placed on him. He must follow exactly a long, carefully-prescribed series of manipulations of &assware and chemicals, make many observations, and when done, interpret his results in terms of reactions he may not have performed hefore. If, after many hours in the lab, the expected results are not achieved, the instructor has little hope of ever finding out if the student made an error in technique, observation, or reasoning. Any success achieved is diminished by the recognition that the cookbook treatment of the subject eliminates the need for thinking. In an effort to circumvent these problems, a lesson simulating a part of qualitative inorganic chemistry has been written in the TUTOR language for the PLATO computer system.' This lesson sets a different goal for the student. His task is to separate a mixture of four ions whose identity he knows. He must shift equilibria, fonn compounds, and selectively precipitate or dissolve the metal comoounds. A computer simulation is especially effective for teachine oualitative chemistni because manv of the time-consuming procedures necessary for obtaining good results such as centrifueine and washine orecioitates can be simulated. student: can more easiGAkeepsight of the longrange problems and goals. The guiding philosophy of this lesson is to stress chemical reasoning rather than lahoratory practice.
Figure 1 . An example of the main display after the student has added Several reagents. Top: The four ions orginally in test tube number 1 are shown. Middle: The student has Indicated that he wants to add HzS test tube 4. Bottom: A record of what is in each test tube is shown: color. pH, and last reagent added. Left: The reagents avaiiable far this separation are displayed
A
Lesson Description A student types in his name and is then given information about the reagents he may use as he solves the simulated problems that follow. The amount of information given ranges from a few words that define the addition of chloride ion to a 125-word explanation of the reactions of sulfides. Next the student is told the identity of the four randomly-selected metal ions that have been dissolved and placed in test tube number one (see Figure 1). The student's task is to separate the four metals into different test tubes. He is shown a list of five reagents which he may add to his ion solution. By adding these reagents one a t a time in any order, the student may form or dissolve precipitates. After each reagent has been added, the student is informed if a precipitate is present, and if so, its color (see Figure 2). A computer routine analyzes the colors of the precipitates present in each test tube to predict the color of mixtures. When a precipitate is present, the student is told that centrifuging, decanting, and washing have taken place and that the decantate has been poured into an empty test tuhe for further use. When the student has completed the separation, he tells the computer which test tuhe each metal is in. Grading of his performance is based on completing the separation and correctly locating the metals. Totaled and averaged scores and subscores are recorded for the instructor's use. When finished with one set of ions, a student is given a new problem with different ions and reagents. 'Alp&, D., and Bitzer, D. L., Science, 167,1582 (1970). 2Grandey,R.C.,J. CHEM. EDUC., 48,791 (1971). 556
1 Journal of Chemical Education
Figure 2. An example of a display which mtarma the student about the results of the reaction he attempted. LAB, DATA, and NEXT are keys on the student's keyset.
Using this lesson a student has more freedom to experiment with alternate methods than he has in a lab or in other comouter-assisted instruction oroerams based on the traditional approach. In order to ailow the student the freedom to add reagents in whatever order he chooses, the PLATO computer had to be taught some inorganic chemi s t ~ The . formulas. solubilities and . oreci~itate colors of . 75 compounds containing one of 19 different metals were described to the computer. The reactions of each of these compounds with several (typically five) reagents were stored in the computer. Around this chemical data-base the rest of the lesson was written. Whenever students request help, the computer finds i n the data-base the appropriate information and displays it. Two kinds of options are available. One type offers the student additional help relating to the reactions he's running and the problem he's solving. This kind of option causes little or no interruption in the progress of the student towards separating his metals. For example, he may find the location of a metal, its current chemical form (e.g., [Ag(NH&]+), or ask what reagents it reacts with. After adding a reagent to a test tuhe, he may request to see the unbalanced equations for all the compounds in that test tuhe (see Figure 3). Sometimes an unusual reaction takes place; for example, the addition of basic sulfide precipitates a hydroxide. After being alerted to unusual
Figure 3. The student viewing the dlsplay shown in Ftgure 2 could press the LAB key and have the above information added to the screen.
reactions, the student may ask for additional information. He may also examine his totaled and averaged scores in several areas. A second kind of option allows student-control of the problem sequencing and interrupts the student's progress towards separation. A student may indicate that be feels he has completed the problem, ask for a fresh sample of the metal ions, or request a different set of ions. He may choose a single ion and test a solution containing only that ion. When he is satisfied that he understands that ion's chemistry well enough, he returns to his original problem. Patterned after one inorganic qua1 teaching techniaue. . , one exercise uresents each ion. one a t a time. so that a student can "run a blank" to acquaint himself with unfamiliar reactions. A review oution offers information about the role of K,,, ampboterism, etc., in inorganic qual. Another option suggests problems for better students to examine. By working randomly-selected problems.. thev . mav . have avoided certain interestina- ion combinations. From the list of options discussed, the instructor selects those which he wishes to be available to the students. Which of the options are selected depends on the backgrounds of the students and the use of the lesson. For example, when this lesson was used as a criterion test, no help options and only minimum problem control options were permitted. From the permitted group of options, the student chooses those which he needs to fulfill his individual learning needs. The lesson includes nineteen ions and nine reagents (see Tables 1 and 2). In order to make each prohlem solvable, some comhinations of ions and/or reagents are eliminated. Approximately 275 different sets of four ions can be generated. 'The instructor can delete unwanted ions from the master list. The reagents were chosen to exemplify most of the common separation methods. Acids, bases, and sulfide may be added at integral pH's of the student's choice. Ammonia is buffered to p H 10, and other reagents cause no pH change. The choice of p H versus "drops of reagent" was made to reinforce the equilibrium concepts and to eliminate the magic of 3 (not 4!) drops of concentrated (not dilute) acid. Thus laboratory practice is de-emphasized in order to focus on chemical principles. Program Operation
The program figures out what reactions would take place, records them, and displays to the student the simulated observation. When grading, PLATO checks its results against what the student reports. No sets of ions or answers are pre-stored. Any method of solving the prohlem is counted correct if it results in all four ions in different test tubes after 12 or fewer reagent additions. Many correct solutions exist for each set of four ions: the 19 ions form about 75 species which undergo about 200 reactions, many of which are pH-dependent. The author will supply flowcharts and general directions on request. The students' progress can he observed during the class and afterwards. As members of the class make errors locating their metals and when they investigate ions one a t
a time, counters for each ion record the difficulties of the whole class. One student terminal may be used to continuously monitor student comments to PLATO as well as the above information about troublesome metals. At the end of the class, hard-copy information is available about each student. T o evaluate a student after a 3-4 hour class session, the instmctor first looks a t each student's totaled and averaged results. There are 15 measures of such things as kinds and amounts of help, total errors, etc. However, averages and totals do not show ability that increases with time. Also, trouble with certain ions or reagents may drastically lower an average score. This kind of information is sorted by the computer but the analysis is left to the instructor. Results
This lesson cannot he quantitatively compared to traditional instruction because the goals and auuroaches to the topic are different. ~urthermore,this les& differs from most other CAI lessons in that it has no end. Knowledge is acquired by gaining experience from the simulation. As a teaching tool the uroaram has met its obiectives: i t provides a m& for students to deal with many example; of qualitative chemistry in an efficient and interesting manner. This program has been used by approximately 200 university and community college students; chemistry majors and non-majors. Students have used the PLATO lesson before, during, and after regular classroom treatment of this subject. The lesson has typically been available for as short a period as two consecutive hours and for as long as three 4-hr periods. Despite the long class sessions, few students left early or took suggested breaks. After a short familiarization with PLATO, the reagents, options, and operations, students spend 10-15 min on each simulated problem-a considerably shorter period than the time required to solve an unknown in lab. Bright students average 5 min/problem and correct solutions in less than one minute have been achieved. Many comhinations of the available options have been used. Even a student who takes the lesson poorly-prepared is able to find enough help as to feel successful rather than frustrated. There are no penalties for requesting help; furthermore, student evaluations indicate great appreciation for being able to find aid quickly, easily, and discreetly. There are so many kinds of help available that few students use them all regularly; instead, students develop their own styles of attacking problems. Although the approach of this lesson was originally designed for use in the medium of computer-assisted instruction, Dr. Robert C. Grandey of Parkland College, Champaign, Ill., has developed and used lab exercises that parallel the student's computer experience in this lesson.2 Table 1. Available Reaaents and Their Effects
Reagents
Special characteristics
OH-, SZHzOz, B a ( N 0 h NHJ Hot water CIHNOs. HC1
Amphaterism,pH dependence Redox and precipitation of Cr Ammine fokmation PbClz dissolution Oxvchlaride oreci~itation oxidizing ve;sus ion-oxidizingacid
Table 2. Master List of Available Ions
Volume 50, Number 8, August 1973 / 557
Acknowledgment
The author is grateful to Dr. Robert C. Grandey and Dr. Alan M. Muirhead for help in programming. Valuable suggestions came from Dr. Gilbert P. Haight, Jr. The co-
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/ Journal of Chemical ducat ion
operation of Dr. Donald L. Bitzer, head of the Computerbased Education Research Lab, and Paul Tenczar and Richard Blomme, developers of the TUTOR language, was appreciated. The study was supported by the National Science Foundation grant GJ 29981.
