ebook img

THE DEPARTURE OF N-BUTFORANE AND N-BUTANE SOLUTIONS FROM IDEALITY PDF

60 Pages·01.971 MB·English
Save to my drive
Quick download
Download
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.

Preview THE DEPARTURE OF N-BUTFORANE AND N-BUTANE SOLUTIONS FROM IDEALITY

The Pennsylvania State College The Graduate School Department of Chemistry The Departure of n-Butforane and n-Butane Solutions from Ideality A thesis John Wilson Kausteller Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy January 1951 Approved: ead, Department or Chemistry Acknowledgement I am indebted to Dr. J.H. Simone for his suggestion of the problem and his continued interest in it. To Dr. T.J. Brice go my thanks for his aid and helpful advice. I wish to thank the Minnesota Mining and Manufacturing Company, sponsors of the project of which this study was a part, for the opportunity to do the work. 353399 TABLE OF CONTENTS Introduction Theory of Solubility of Non-Polar Substances Interpenetration Postulates Results and Conclusions Liquid-Vapor Equilibrium Mutual Solubilities Heats and Free Energies of Solution Solubility Parameters Entropy of Mixing Calculation of the Interpenetration Factor Some Physical Properties of n-Butane and n-Butforane Experimental Source and Purification of Materials Vapor Pressures of n-Butforane Liquid-Vapor Equilibrium Apparatus Mutual Solubility Apparatus Details of Operation of Equipment Analysis of Mixtures Densities of Mixtures Volume Changes on Mixing Summary Bibliography 49 Appendix: Experimental Data I Freezing Point of n-C^F^Q 50 II Vapor Pressure of n-C^F^Q 51 III Liquid-Vapor Equilibrium 52 IV Mutual Solubility 54 V Densities of Mixtures 55 1 INTRODUCTION Investigations of the properties of solutions are aimed at identifying their properties with a particular type of force or forces "between the molecules. One approach to the problem is the study of systems composed of non-polar mole­ cules. The ultimate in this respect would be the rare gases. They are spherically symmetrical, show no apparent associ­ ation or chemical combination and are non-polar. Unfortu­ nately their low boiling points and high price make them undesirable tools for research. Fortunately, however, the fluorocarbons offer a "high boiling rare gas" substitute in that they have the attributes of the rare gases except for the spherical symmetry. Vhile the latter property is lack­ ing, they do have smoothed-out force fields. Lack of spher­ ical symmetry may in reality be an advantage as moet real molecules are not spherically symmetrical. Because of their unique properties they have been the subject of interest in some instances. j Hildebrand and coworkere ^*2,3 have shown that the fluorocarbons they have investigated fit the Begular Solution Theory even though the solubilities of solids and liquids are exceedingly low compared to the analogous hydro­ carbons. They have also predicted with a fair degree of accuracy the critical temperatures of "binary liquid mix­ tures having a flucrocarbon as one of the components. In the study of the system n-pentforane - n-pentane Simons and Dunlap ^ found large deviations from Raoult*s law. The components of the system were nearly identical with respect to "boiling points, melting points, molecular dimensions, energies of vaporizations, and electron polar- izabilities. Since the materials also show no association the deviations were attributed to pentane having a degree of liquid structure dependent on the interpenetration of pentane molecules with each other in a gear-like manner. The fluoroc^ rbon molecules were assumed not to interpene­ trate appreciably with each other or with hydrocarbon molecules. Since the study indicated the possibility of the adoption of fluorocarbons as a basis for solubility theory investigations it would be highly desirable to pursue the matter further. The system n-butforane - n-butane is at­ tractive for several reasons. It would serve as a check on the five-carbon-system, being next in the homologous series. The physical properties of the components are even closer than those of the other system, the properties of hydrocarbons and fluorocarbons vs the number of carbon atoms being closest at about four carbon atoms. As with the previous study the materials are non-polar, show no apparent chemical combinations, are of approximately the 3 same molecular size* and have a sufficiently large differ­ ence of molecular weights to make analysis possible by gas density measurements. THEORY To treat a system of non-polar molecules Hildebrand* 8 theory of Regular Solutions 5 has proven to be of general application. In the development of the theory the liquid is built up of molecules brought from an infinite distance to the equilibrium distance r. In this fashion the potential energy of a mole of a pure liquid may be expressed as CD where B° is the energy of vaporization at some temperature T, N is Avogadro's number, V is the molal volume* r the distance of closest approach of the centers of the mole­ cules and k is the attractive force constant between two molecules. In adopting k to represent the force constant an ex­ pression of the type postulated by Lennarlfi*Jones ® is used. Here € is the total force constant between two molecules* with j and k respectively the repulsive and attractive constants. The distance between molecular centers is r and n is a number, usually 12. Hildebrand neglects the repulsive constant j and retains only the attractive term, £ k/r. He further assumes a geometric mean between the attractive constant k12 for two unlike molecules and k ^ and k22 for like molecules. Thus in a binary mixture the basic equation for E° is r Where € is the force constant, W a probability function expressing the arrangement of molecules around a central molecule and the rest of the quantities are as described previously. Taking W as nearly equal to one, and sub* stituting for € we have equation (1). For a solution of two components the total E for the solution would be the sum of the individual E*s. (4) Where n is the number of moles of each component 1 or 2, and the subscripts 11, 12, 22 refer to molecular combin­ ations. This may now be differentiated with respect to &X* giving the partial molal potential energy of species 1 in solution. Remembering that VsV^n^-f-Vfor no volume change on mixing,, and subtracting E° for the pure com- ponent we have the potential energy change for component 1 in placing a mole of pure component into an infinite quantity of solution. E - E ; = ZvN’f-.lrt-fv, fe f - f o d r ‘ ' L wiv< “*■ nzviJ L ' 2 J (5) - Here no cognizance has been taken of the volume changes occuring on solution. If this is recognized the equation becomes _ p r®9 ‘ V' *1* .09 pCO ~l (6) _L f _ J£u-dr - -L I - J&dr I H *•; w r * J rru.i rn Hildebrand uses equation (5) to predict the properties of solutions from those of the pure components, in as much as partial molal volumes are only obtained from measurements on solutions, and the aim of the theory is to predict the properties of solutions from the properties of the pure components. The energy of vaporization has been taken as indicative of the forces acting in a pure liquid, and is set equal to the potential energy change observed in condensing a mole of infinitely separated molecules. For each of the terms in the brackets in equation (5) we can write its equivalent in terms of the energy wf vaporization and molal volume.

See more

The list of books you might like

Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.