Gene Wise Viroinio Militorv Institute u .ex'ngton, 24450
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Computer Programs for Undergraduate Physical Chemistry Students
Computer programs in Fortran IV (modified) for the IBM 1620 have been written and tested for several undergraduate physical chemistry laboratory experiments and classroom problems. Other programs solving undergraduate physical chemistry problems have been written for the Marchant Cogito 566 P R programmable desk calculator. This work was done with the aid of a National Science Fouudation COSIP grant. Two students at the Virginia Military Institute, William E. Daniel and Harry R. Partridge, participated in the project. Program listings and operating instructions for all programs described below are available from the author. All laboratory- ex~eriments are based upon experiments . described in standard physical chemistry caboratory references are given, copies of all texts,for necessary subroutine subprograms will also be provided. When requesting copies of programs, please indicate, if possible, which programs are desired, or which sets of programs (Fortran IV or Cogito 566 PR) are desired. A list and description of all programs follows. Fortran IV (modifled) Programs 1) Molecular Weigh1 by the Method of Dumas. Fromvapor density measurements, obtained by the classical Dumas method, the program calculates the molecular weight of benzene or any other volatile liquid compound, using the Ideal Gas Law equation, the Bertbelot equation and the Van der Waals equation. 2) Molecular Weight by the Method of Vieto7 Meurn. From vapor density measurements, obtained by the classical Victor Meyer method, the program calculstes the molecular weight of benzene or m y other volatile liquid compound, using the Ideal Gas Law equation, the Berthelot equation and the Van der Wads equation. 3) Molar Refraction. The program corrects to 2J°C all readings of index of refraction of a given liquid compound and calculates the average index of refraction. The molar refraction of the compound is then calculated from the average index ofrefraction, the molecnlar weight, and the densky of the compound. The proeram also calculates the averaee deviation. the standard deviat,ion. orohahle ~ ~ and - t,he ~ ~~-error of the measured indices of refraction. 4) Viscosity. Times of flow of a liquid and a reference liquid (water) through an Ostwald viscometer, a t four selected temper* tures, are averaged, and the viscosity of the liquid then calculated from the average time of flow and density, for each temperature. Then, using R. straight-line least-squares curve fitting subroutine, the slope and intercept of the plot of the logarithm of viscosity versus the reciprocal of absolute temperature are calculated. 5) Vapor Pressure. The vspor pressures of liquids a t various temperatures are calculated from isoteniscope and manometer measurements, and, by means of a straight-line least-squares curve fitting subroutine, the heat of vaporization of the liquid is calculated from the slope of the plot of the logarithm of vapor pressure versus the reciprocal of the absolute temperature. 6) Suvfaee Tension by Ring Method. The program calibrates the scale of the DuNouv tensiometer from ma98 versus scale read, pn,gr;lm rslrulntc. data. 'l'hw, for rach .~rlowls t ~ l i w l rhe the d113 l ~ ? c r s i w1) 0~obtain. flonl icfcrrnre iklde., I ht, *hap+ 10rrettIun i n u w fwm which .orfncc trn,wn uf rhr 1 1 < p dcan I T dl.termined ~~~~
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7) Equilibrium Conslant of a Homogaeous Chemical Reaction. Program calculates the equilibrium constant for each of several equilibrium mixtures consisting of acetic acid, ethanol, ethyl acetate, and water. Data input consists of initial weights of the reacting substances and the volume of standard base titrated to det,ermine the amount of acetic acid oresent in the eauilibrium mixture. The program calculates the molar concentrations of all the reacting substances from the amount of acetic acid present at equilibrium. 8) Distribution Coeflcient. Molar concentrations of an organic solute (as acetic acid), distributed between two solvents immiscible to each other (as water and ether), are ealcul~tedfrom malytical data. Then the distribution coeffioient, a. heterogenwus equilibrium constant, is calculated from molar ccancentrations, for each trial. The program also recalculates the distribution coefficient, obtaining a more accurate value in the case where the organic solute associates in the organic solvent phase. This utilizes the st,raight-line least-squarescurve fitting subroutine to obtain the dope of the plat of the logarithm of the concentration in the organic phase versus the logarithm of the concentration in the aqueous phase, 9) Mole Fractions in a Binary Mizture. The program calculates the mole fractions of each of two compounds in two-component mixtures, from the weights and the molecular weights of the two compounds. This program is used in an experiment which determines the phase diagram of s. two-component system. 10) Weight Percenl in a T a a r y Liquid Miztu~c. The program calculates the weight percent of each component in threecomponent mixtures of benzene, isopropmol and water, a system of one partially miscible pair. This program is used in the determination of the phase diagram of the above three-component system, and may be modified for any three-component liquid mixture. 11) Conductance of Strong and Weak Electrolytes. The cell constant is first calculated from the measured resistance of a standard potassium chloride solution. Then, for any electrolyt,e, strong or weak, the specific conductance and the equivalent conductance are calculated for various concentrations of the electrolyte. For a weak electrolyte, the degree of dissociation and the ionization constant are also calculated. 12) Standard Potentials of Metal Electrodes. The program solves the Nernst Equation for the standard electrode potential of any metal electrode, using as input data. the measured cell potential, the potential of the reference electrode, theconcentration of the electrolyte, and t,he mean activity coefficient of the electrolyte. 13) Rate of Inversion of Sucrose. In the inversion reaction of sucrose. the relative concentration of the sucrose. a t various intervals nf time. is obtained from the measured anele of rotation,. wine ~, a. palsrimeter. The program then calculates the first-order rate constant a t each interval of time and calculates the average of the rate constants. 14) Mean Aetiuity Coeficients. Using an electrochemical cell without liquid junction and consisting of one electrode whose potential is khown, the cell potential is measured a t several conrentrations of the electrolyte. The program calculates the mean activity coefficient of the electrolyte a t each concentration, and, calling on a straight-line least-squares curve fitbing subroutine, calculates the standard electrode potential of the second electrode making up the cell. 15) Clausius-Clapeyron Equation/Arrhanius Equation. At the appropriitte signal from bhe u e r , the program calculates any one or more of the variables in the Clausius-Clspeyron Equation or Arrhenius Equation. 16) Gibbs Free Energy Change. The program calculates the ~~~
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Gibbs free energy change far a chemical rereaction a t any desired temperatwe. Data input includes standard enthalpies of formation, standard fr:e energies of formation, and the molar heat capacity equat,ions for all the reactants and products of the reaction. 17) Treairncnt of Errors. This is a subroutine subprogram which calculates, from a. set of measurements of a quantity, tho arithmetic mean, t,he average error, the standard deviation and the probable error.
Marchant Cogito 566 PR Programs 1) Molar Rejractim. The program calculates the molar refraction of a. liquid compound from the index of refraction, the denshy, and tho molecular weight of the compound. 2) Mole Fraction in a Binary Mizlure. From two data. entries-the weights of the two compounds in a binary m i x t u r e the program ealculntes the male fraction of one of the compounds
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in the mixture. Molecular weights of the two compounds are initially entered as constants. 3) Calorimetry. The first, part of the program calculates the heat capacity of a calorimeter from the measured temperature rise produced by a reaction between a strang acid and a strong base. The second part of the program then calculates the heat of neutralization of an unknown acid from the measured temperatme rise in the reaction between the acid and a standard base. The program requires eight data entries. 4 ) Clausius-Clapeyron Erpation/Arrhenius Equation. Each of four seoarate Droerams calculates one of the variables of the Clausius-Clapeyron equation or the Arrhenius Equation. Three of the programs require five data entries and the fourth program requires four data entries. 5) Twatmenl of Errors. Two consecutive programs, programmed separately, calculate the arithmetic mean of a set of measwements, the sum of the deviations from the arithmetic mean, and tbe :iom of the squares of the deviations from the arithmetic rncito.
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