Activity Corrections in Acid/Base and Precipitation Titration Curve Calculations G. M. Muha Rutgers University New Brunswick. NJ 08903
The use of the concept of the titration curve in developing the topics of acidbase and precipitation equilibria is well known. Although computer programs for calculation of pH tit,rntion curves are readilv available (17). remarkahlv the inclusion of actkity corrections in the computations is omitted. To correct this deficiencv we have written r)nxrams for hoth pH and precipitation titiation curve calculati&s. These programs are used by students to check their work on acid1 base and precipitation equilibria in two standard physicalanalytical laboratory exercises (18). As a part of these exercises the student is required to determine the concentrations of a set of samples supplied for chemical analysis along with the equilibrium constants for the reactions involved. Thus from the results of some ten hours ~~~
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Journal of Chemical Education
of laboratory work, the programs enable the reconstruction of the "raw" experimental data for confirmation of the student's solution to the problems posed. By including activity corrections in the programs, the theoretical results ohtained are assured of being correct within the limits of current knowledge of the theory of solutions. The nroeram for the acidbase case admits the calculation of the &&on curve for the strong base titration of a strong acid. a weak acid (mono-, di-, or triprotic), or a mixture of the t w o . ~ h eprecipitation calculation~appliesto the titration of a single anion species or to a mixture of two anion species (e.g., the chloride and iodide ions). In hoth the acidhase and precipitation cases, the appropriate equilibrium constant(s), concentrations of the reagents, aliquot size, dilutions, etc., are specified in the interactive mode to simplify the input format for the student. The activitv corrections are introduced in terms of the extended form bf the Dehye-Huckel theory although other more sophisticated formulations may he readily incorporated in the program if desired. The proarams are written in VS-APL hut will run under APL-sv o r - ~ P ~ - P l uwith s only minor changes on any system that supports these languages. The program outputs, a plotted titration curve and a table of the data as plotted, are formatted so as to print a t video terminals or line printers that have the APL character set, or on a Tektronix 4U13 graphics terminal. The programs and their sutrroutines require a negligible fraction (
