derstanding the thermodynamics of solar space heating. These include the role of thermodynamic efficiency in solar space heating as applied to types of collector (e.g., active versus nassive): . , the relationshin between heating demand, solar inBolation availability, and the calendar year; and the significance of the rate of inflation in the price of the nonsolar fuel and the rate of interest in financing the collector in determining the economic feasibility of each model collector. The program uses interactive Applesoft 11, is 501 statements long, with 116 lines of instructions and examples for new users. The program is run on APPLE I1 PLUS (48K). Documentation including listing, sample run, and instructions provided free upon request. Copy of program on APPLE I1 floppy disk: $8.00 (we will provide disk). Send correspondence to Dr. Bruce Mattson. Checks should he made payable to the chemistry department.
Graphical Simulation of Radioactive Decay E. D. Cavln and C. S. Cavln
6008 Mountainclimb Drive Austin. TX 78731
In this simulation we wished to illustrate two features of radioactive decay: (1) its random nature and (2) the fact that half of a quantity of an element decaying should do so in the half-life period of the species. Additionally, it was our purpose to provide a simple, nonthreatening, interactive introduction to using computers. The program was designed for students in nonscience majors' chemistry classes. The users of this simulation are to determine, knowing a given starting numher of atoms, the numher of atoms decayed during, and left after, a given half-life period. After an introduction on the screen, the program displays 256 small blocks, representing a sample of "atoms" of a radioactive substance, in a box on the video screen. During the period of each halflife, blocks are randomly turned off to indicate radioactive decay of some of the atoms. The half-life durations are not constrained to he exactly equal, hut each half-life period usually is of similar duration because, although fewer "atoms" decay in later half-life periods, it is more time-consuming for the program t o find randomly an atom that has not decayed in these periods. After each half-life period, time is "stopped" so that students may answer questions as to the numher of atoms that have decaved and the numher which remain undecayed up to that point: correct answers are displayed in column6n either side of the box of atoms, and questions are asked in a location below the box. The box of atoms remains on view during the entire program, but, of course, contains fewer and fewer atoms as time progresses. The simulation introduces students to the concept of half-life, specifically, that half of an existing quantity (rather than half of an original quantity) of a radioactive substance decays in a given half-life period. Although designed for nonscience majors, it may not he inapplicable for science majors, some of whom, in our experience, have been confused by this point. We reviewed 133 questionnaires from student users who were doing the program for extra credit. Student comments were unusually favorable; most enjoyed the program and only afew did not like it. Surprisingly, many said that the program was easy-even, in some cases, too easy. The concepts and arithmetic are not completely trivial, but the students indicated, in general, that they felt that they had little trouble with the nromam. Students freouentlv noted that thev had been uneisy;bout using the computer, hut afterward-thought i t was fun andlor interesting. Manv thought - that the computer was a good way to learn. The program is written in BASIC for the TRS-80 microcomputer, Model 1.I t has, and should need, little documentation. I t consists of about 160 lines and takes up about 5K
598
Journal of Chemical Education
bytes of memory. It is available from the authors as a listing on receipt of a self-addressed, stamped envelope.
Computer-Assisted Evaluation of Commercial Antacids Rafael Infante-M8nder Catholic University of Puerto Rico Ponce. PR 00732 Applications of classical methods of quantitative analysis to commercial products are becoming popular in undergraduate general and analytical chemistry laboratories. The acid neutralizing power of commercial antacid preparations determined hy a titrimetric procedure is a commonly used application for neutralization methods. In this experiment, a commercial antacid tablet is dissolved in a measured excess of hydrochloric acid, the solution boiled briefly, and the excess hydrochloric acid hack-titrated using a standard solution of sodium hydroxide. A variety of commercial brands of antacids can he evaluated on the basis of this procedure. We have written a program which allows the student to enter the exoerimental results into the computer for data evaluation. The program first calculates the concentration of the hydrochloric acid and the sodium hydroxide solutions used in the experiment. The student is required to supply the weights of the primary standard and the volume of titrant used. Then the computer asks for the volume and concentration of the hvdrochloric acid and the volume and concentration of the sodium hydroxide solutions used and calculates the numher of moles of acid neutralized by the tablet. The weight effectiveness of the antacid is calculated by using the weight of the tahlet and the neutralizing ability of the tahlet. The cost effectiveness is determined by using the cost of the tahlet and the neutralizing ability. The program is written in BASIC for a TRS-80 Microcomputer. All instructions to a student user are in Spanish. Listing of the program and typical student data can he ohtained upon request from Rafael Infante-Mhdez, Department of Chemistry, Catholic University of Puerto Rim, Ponce, Puerto Rico 00732.
Stoichiometry Drill and Tutorial in Spanish Guldo A. Concha. Raul L. Contreras, J o e R. Corbalan, and Franklln 0. Bacados Oficina de Education Quimica Catholic University P.O.Box 114-D Santiago. Chile This program presents a series of related questions about stoichiometrv t o the student user. Questions are chosen in sequence from each of the following categories: 1) What is the molecular weight of a compound? 2) How many moles are there in a grams of a compound? 3) How manv erams of an unhvdrated compound are there in o grams of &; hydrated one?. 4) How many water molecules are there in a grams of a hydrated rornnn,,nd? 5 ) H w manly H atoms are there in a grams of n eompaund'! 6) How many grams ofa cumpuund are rhrre i n n numlwr uf i t s
molecules?
I ) What is the percent of an element in a given compound? 8) How many gram-atoms of H are there in o grams of a com.-
pound?
9) How many grams of a hydrated compound would contain a
known amount of water? 10) What is the percent of water in a hydrated compound? All numerical data and the identity of the compound are selected randomlv bv the comDuter so that each student will The student uses a periodic receive a unique set of
