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The System : Hydrazine Hydrochloride-Water-Ethanol

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The System : Hydrazine Hydrochloride-Water-Ethanol TRE SYSTEN: HYDRAZINE HYDROCHLORIDE-WATER-ETHANOL by LAWRENCE LEE HUMPIIREYS A THESIS submitted to OREGON STATE COLLEGE in partial fulfillment of the requirements for the degree of NASTER OP SCIENCE June 1960 APPROVED: Redacted for privacy Professor Chemistry In Charge of' Major Redacted for privacy Chfrnari of Department of Chemistry Redacted for privacy Chairman ofchoo1 Graduate Committee Redaóted for privacy Deaí ±' Graduate School Date thesis is presented Nay 9,. 1960 Typed by Lilah N. L otter AONOWLDGI1EN This opportunity is taken to thank Dr. 1. C. Gilbert for his help and. guidance throughout these investigations. TABLE OF CONTENTS Page INTRODUCTION. i EXPiRIMENTAL AND SAKLL CALCULATIONS. 9 DIbOUSSION AND CONCLUSIONS. , . 21 Figure I Typical Isotherm for a Salt-Water- AicoholSystem.......... 3 II Tie Line Determination . 6 III Graphical Determination of 1'lait Ioint Composition. 19 IV Isotherm for the System N2H501- C2H5OH-H20 at 15°C . 23 V Isotherm for the System N211501- C2H5OH-1120 at 25°C . 2k Table I Preparation of Samples for Soiubility Curves. li II Composition of Saturated Solutions of N2H5C1. 13 III Composition of Samples on Binodai Curve. 1k IV Tie Line Determination . 18 THE SYSTEM: HYDRA Z INE HYDROCHLORIDE-ÁATER-ETHANOL ÏNTRODUOT ION During a recent investigation, it was discovered that the salt hydrazine (I) hydrochloride, N2H5C1, caused an alcohol-water system to form two liquid phases at cer- tain concentrations. This is true of methanol, ethanol and propanol. The purpose of the investigations con- cerned with this paper will be to elucidate the phase diagram of the system ethanol, water, and hydrazine (I) hydrochloride at two temperatures, 15 and 25°C. Since the beginning of the fourteenth century, when potash was used to concentrate alcohol from wine (2), scientists have noted and studied the phenomenon now known as tsa1ting out". In 1897, systems exhibiting tis property were classified into four types of systems by 3chreineruakers (8): (a) each of the binary systems forms two liquid phases, (h) two of the binary systems form two layers, while one does not, (c) only one of the binary systems forms two liquid phases, and (d) none of the binary systems form two stable liquid phases, but the mixing of all three in certain proportions does cause separation of layers. The system wider consideration is 2 in this last group, since none of the binary systems produce two liquid phases. Many salts, oxides, and hydroxides cause the precipitation of an organic liquid from water, but as the miscibility with water increases, the number of such compounds seenis to decrease, so that potassium carbonate has apparently been the only salt found previously which will precipitate methanol from water (14). Apparently, as the solubility of the salt in water increases compared to that in the third component, so that the preferential solubility, or distribution coefficient, for water in- creases, the saltin, out power increases. The usual isotherm for a salt-alcohol-water system such as the one under consideration is similar to the one shown below (3). Points a and b give the solubility of the salt in pure water and alcohol, respectively, The area o-b-d-o is a two phase area, solid salt and saturated alcohol- rich solution. The area o-a-c-o is also a two phase region, solid salt and saturated water-rich solution. The area c-k-d-c is a two liquid phase area, and the line c-k-y is known as the binodal curve. The line x-y is a tie-line, which joins compositions of phases in equili- brium with each other. The point k is known as the 3 water salt alcohol Figure 1 Typical Isotherm for a Salt-Water-Alcohol System plait-point, and is the critical point at which the tie-lines vanish, or the composition of the two phases is the sanie. The area o-c-d-o is a three phase area, solid salt and liquids of composition e and d. By the Phase Rule, this must be an invariant area. If we ignore the vapor phase and pressure variable (a reduced system), this may be shown by F = C-P+1 where k C number of components = 3 P = number of phases = 3 F = degrees of freedom = The one degree of freedom which remains has been used in holding the temperature constant. In other words, addition of any of the components will not change the composition of any of the phases until one of them dis- appears. The last area, a-x-k-y-b-alc-H20, is a region of one liquid phase, which is unsaturated. With this background, the proposed methods for analysis of the various portions of' the curve will be discussed. The solubility curves can be determined by saturating solutions of known alcohol-water content with hydrazine hydrochloride, and then determining salt con- tent by titration for the chloride ion with silver nitrate to a dichiorofluorescin end-point. Points on the binodal curve, c-k-d, can be ob- tamed by making up solutions of known hydrazine hydro- chloride and water content and. then titrating to in- homogeneity with ethyl alcohol. This endpoint can best be detected by means of a dye, spirit blue, which is colorless in water solutions but is a bright blue in alcohol solutìons (4). 4hen lithoinogeneity is reached 5 in the titrations, the alcohol phase appears as a bright blue ring around the top of' the water layer. If the color change is not observed, but a murkiness does appear, the line intersected is the solubility curve rather than the binodal curve. 'The tie-lines of' the binodal curve can be fixed by separating two layers in an equilibrium system for which the total composition is known. The two layers are analyzed for hyd.razine hydrochloride content by titration with silver nitrate. By intersecting the pre- viously drawn bimodal curve with a line which depicts the percentage salt, the position of the point which termin- ates the tie-line is fixed. If' this is done for both layers, and a line is drawn between the resulting points, this line must pass through the point which depicts the total composition of the system. This method is similar to that of Frankforter and Frary (k). To locate the point known as the plait point, an adaptation was made of the Bacliman equation (1) suggested by an article of Heric (5). The equation has been applied chiefly to ternary systems of liquids of' which two are immiscible. By using ethanol and hyclrazine hydrochloride as the "immiscible'7 pair, it is believed that the method can be successfully applied to the water layer rye omposition alt in alcohol layer alcohol Figure 2 Tie-Line Determination present investigation. The tie lines of a ternary system which exhibits two liquid phases are very rarely parallel, so that the interpolation of known tie line data is difficult and. often unsatisfactory. flany attempts have been made to correlate tie lines, one of which is the Bachrnan equation (7). This equation, which relates the ratio of the major non-consolute components to the composition of one of the phases, is expressed empirically by (x)(y) = ax + by 7 where A and B are non-consolute components. Here, x is the weight percentage of A in the A-rich layer, y is the weight percentage of' B in the B-rich layer, and a and b are empirical constants for a given isotherm. This equation may be rewritten in the form x = a(x/y)+b By plotting x versus x/y, a straight line results which correlates the tie line data. By picking a value of x from this line, the value of y which must be in equili- briwn with it can be found. This line must pass tbrough the plait point. If now another straight line is estab- lished from points of the binodal curve plotted in the same manner as above, this latter line must represent the locus of points somewhere upon which the plait point must lie. The intersection of these two lines then gives the location of the plait point. This method works very well for this liquid-solid system by taking ethanol and hydrazine hydrochloride as the non-consolute pair. The area under the binodal curve, and the plait point, are dependent upon the temperature. Tinuiierans (10) stated that all systems have an upper and a lower critical temperature. In this range, the two liquid phases may be formed at certain concentrations. Outside ri L'-J of this range, however, the two liquid phases cannot be formed. The critical temperatures cannot always be realized experimentally, due to the fact that they may lie above the boiling point or below the freezing point of a liquid component. Usually, however, at least one of the critical temperatures can. be found. EXIiR flLNTAL The hydrazine (I) hydrochloride used was prepared by the reaction of liquid hydrazine with chemically pure hydrochloric acid. The reaction proceeds according to the following equation; N2H4 + HOl -. N2115C1 The hydrazine was placed in a beaker in an ice-bath. The hydrochloric acid was added to the reaction vessel drop by drop from a self-filling burette with constant stirring. The time for addition of acid was about three hours. The end-point for the reaction is the neutral color of methyl orange indicator, because if the solution is more acidic than this, sorne dihydrochioride forms. The reaction mixture was evaporated until crystals formed and was then crystallized from 80% methanol. The preci- pitate was collected on a sintered glass filter with suction and was then dried at 60°C and.
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