execute. The BASIC programs were written utilizing simple variable names, and therefore they can be easily adapted to most microcomputer systems with only minor modifications. Although designed for hardcopy terminals, the programs will function on any CRT terminal that displays a minimum of 80 characters per line. A set of listings is available from the author. Please send a self-addressed stamped 9 X 12 envelope with sufficient postage to cover cast of mailing the 6-02 package.
Calculator Program for Analysis of a Complex by Job's Method J. E. House, Jr.
Illinois State University Normal, llllinois 61761 The usual technique for determining the composition of a complex that is used in instrumental analysis (61, inorganic chemistry (7), or in research ( 8 ) is Job's method. In this method. the mole ratio of the components of the complex is varied while keeping the sum of thk two concentratiois constant. Then, some property that is linearly related to the concentration of the complex is measured. The maximum amount of complex is formed in the solution where the molar ratio of the components is the same as it is in the complex (9). Therefore, a plot of the measured property vs. the molar ratio of constitute& will produce a mix&um a t the same value as that ratio in the complex. If a single, very stable complex is formed, the result will be two line segments that intersect a t the maximum. Frequently in practice the result is a curve which has a much less distinct maximum, the position of which must be determined graphically (see Figure 2). A nroeram bas been written for use with the Texas Instruu ments TI-59 programmable calculator that locates the maximum bv determinine linear relationshins for two vortions of the curie and c o m p u h g the point of tKeir intersection. This technique saves time and can simplify the procedure when the property/composition curve is flattened andlor skewed in such a way that the desired maximum is not simply the "highest point." The program begins by entering the data for the total concentration, the concentrations of one of the components, and the corresponding values of the measured property. First, the computation fits a linear relationship through points P1 and P 2 (see Figure 2). For this fit, the correlation coefficient (r) is exactly 1.Then, P 3 is included and a linear relationship
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I4l + [el Figure 2. A Jab's plot for the formation of a complex, A + n B S A B , , where A = metal ion and B = ligand. The maximum in the measured propem. P, occurs when the concentration of ligand is equal to that of the metal ion so n = 1 in this case.
132
Journal of Chemical Education
is again fit to the data. For example data, it will be observed now that lr l < 1.This will be due to the fact that the curve is be cohcluded that the ;elationship is still linear, but the discrepancy is caused by experimental errors, not curvature. The computation involves setting a value for the correlation coefficient (p) that will allow for a linear fit within the experimental error of the data but will exclude curvature of the graph. Processing begins with two points and successive points are included as long as lr 1 > p. When including one additional point causes 1 r 1 < p , processing branches to the data for the right-hand side of the graph and a similar linear relationship is established for that portion of the graph. When both linear portions have been established, the point of intersection is computed and then the ratios of the two components are computed to determine the composition of the complex. The program described permits students and teachers of inoreanic chemistrv or instrumental analvsis to measure the " appropriate property of a complex as a function of composition of the solutions and determine the composition of the complex according to Job's method. I t is particularly useful for allowing the rapid analysis of many sets of data without graphing. It also allows individual problems to be assigned with real or hvuothetical data. Further, i t allows the student to see the effects of experimental errors by changing the value of p and seeing any difference in the computed composition of the complex. Using the program, an instructor finds it easy to check student responses to either problems or laboratory d.n:i wirhotl~h,tving I,, prrpare nullterms : r ~ p h > . A
