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Physicochemical properties of the DMSO-Cu(NO3)2-3H2O system
1 2 Mamyrbekova Aig. , Mamitova A. ,
Mamyrbekova Aizh.3 (Republic of Kazakhstan)
Физико-химические свойства системы ДМСО-Cu(NO3)2•3H2O
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Мамырбекова Айг. К. , Мамитова А. Д. ,
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Мамырбекова Айж. К. (Республика Казахстан)
1Мамырбекова Айгуль Кумекбаевна /Mamyrbekova Aigul - кандидат химических наук, доцент;
2Мамитова Айгуль Джанабаевна /Mamitova Aigul - кандидат технических наук, доцент, кафедра биотехнологии, высшая школа химической инженерии и биотехнологии,
Южно-Казахстанский государственный университет имени М. Ауэзова, г. Шымкент; Мамырбекова Айжан Кумекбаевна /Mamyrbekova Aizhan - кандидат химических наук, доцент, кафедра лабораторных дисциплин, медицинский факультет, Международный казахско-турецкий университет имени А. Ясави, г. Туркестан, Республика Казахстан
Abstract: physicochemical properties of the DMSO-Cu(NO3)23H2O system are studied in the concentration range of 0.01-2 M at 298 K. The refraction index of a solution of copper(II) nitrate in dimethylsulfoxide (DMSO) is measured at 288-318 K. The excess and partial molar volumes of the solvent and dissolved substance are calculated analytically. Аннотация: изучены физико-химические свойства - плотность, динамическая вязкость и показатель преломления системы ffMCO-Cu(NO3)^3H2O в интервале концентраций 0.01-2 М при температуре 298 К. Показатель преломления растворов нитрата меди(И) в диметилсульфоксиде (ДМСО) измерен в интервале температур 288-318 К. Аналитическим методом рассчитаны избыточные и парциальные мольные объемы растворителя и растворенного вещества для данной системы.
Keywords: copper(II) nitrate crystallohydrate, dimethylsulfoxide, solubility, refraction index of solution, solution density.
Ключевые слова: кристаллогидрат нитрата меди(П), диметилсульфоксид, растворимость, показатель преломления растворов, плотность растворов.
Dimethylsulfoxide (DMSO) molecules are cationotropic, they form quite strong complexes with copper(II) ions that have coordination numbers from 2 to 4. There are data on the formation of stable [(CH3)2SONO3]- complexes in the presence of water when the nitrogen atom is linked directly with the sulfur atom, although the possibility of such bonding was denied in [1, 393-398]. The existence of Cu (NO3)2mDMSO complexes where m is 2-4 was mentioned in [2, 164].
In this work, we studied the changes in density, viscosity, and refraction index as a function of the concentration of a dissolved substance at 298 K. The refraction index of the DMSO-Cu (NO3)23H20 system was measured over the wide temperature range of 288-318 K.
Copper nitrate crystallohydrate was synthesized according to the procedure described in [3, 345] and recrystallized from water. DMSO was distilled in vacuum (nD=1.4816, p4=1.0764 rcM3).The refraction indices of the investigated solutions were measured using an URL model 1 multipurpose laboratory refractometer (accuracy, 5-10-5), the density was determined by pycnometry with an accuracy of ±0.5 kg/m3, and the viscosity was determined using a capillary viscometer with a capillary diameter of 0.59 mm. All measurements were performed at constant temperatures maintained using a UTU-4 multipurpose thermostat with an accuracy of 0.5°С. The content of water in the crysallohydrate rose as the concentration of salt in the DMSO-copper nitrate system grew, and the system was in fact DMSO- Cu(NO3)2-H20. The presence of small amounts of water (~10 mol %) had no appreciable effect on the physicochemical parameters of dimethylsulfoxide solutions [4, 250] while considerably facilitating the solubility of the salt.
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The refraction index and density of a solution of Cu(NO3)23H20 in DMSO increase as the salt content therein rises (Fig. 1). The isotherms of dependences of the refraction index on the copper(II) nitrate concentration in DMSO are expressed as a broken line (curves 1-5) described by the equation,
n = n0 + b ■ lg C, (1)
where n0 is the standard refraction index of a solution obtained by extrapolating n and loge with a straight line to c = 1 M, and b is the slope of the line. The n0 and b values (Table 1) were obtained by the least squares processing of the experimental data on a computer. The correlation coefficient for the values determined is in all cases at least 0.95, and the confidence level is 95%.
The relative refraction index-temperature coefficient,
E^ = (5lgn0 /dT\ = -2.70-10-4K-, (2)
determined from the data from Table 1, lies low in the temperature range of 288-308 K and is close to the En of pure DMSO (-2.62 x 10-4 K-1). The refraction temperature coefficients of solutions increase in absolute magnitude in the high temperature range (308318 K) up to -3.6 x 10-4 K-1, due obviously to the decomposition of DMSO eigenstructuring. The ionized state of cupric nitrate in solution and the predominant effect of DMSO itself on the optical properties of the system is likely responsible for the slight slope of the n, loge isotherm (b = 0.0068) in the low-concentration range (to 0.4 M).
logc |mol/L|
Fig. 1. Refraction index (1-5) and density (6) of solutions of Cu(NO3)2^3H2P in DMSO as a function of the copper salt concentration at (1) 288, (2) 293, (3, 6) 298, (4) 308, and (5) 318 K
Table 1. n0and b constants of Eq. (1) at different temperatures. In the ranges of Cu(NO3}2- 3H2O concentration (0.01-4 and 0.4-2.8 M}
T, K no b103 n0 b103
0.01- 4 M 0.4 -2.8 M
288 1.4948 7.176 1.5031 25.304
293 1.4915 6.176 1.5012 24.862
298 1.4902 6.375 1.4997 27.063
308 1.4861 6.850 1.4960 26.797
318 1.4811 5.690 1.4929 29.653
As can be seen from the plot, the slope of the n, logc isotherm increases in more concentrated solutions (>0.4 M); this can be explained by the coarsening of the electrolyte particles induced by ionic association, which is likely enhanced as the temperature rises. In diluted solutions, the rise in density with growing concentration of the solution at a constant temperature of 298 K is also slight (Fig. 1, curve 6). Upon moving to more concentrated solutions (>0.4 M), the slope of the p, logc line rises more than eightfold. The high increase in solution density seems to be caused by the ionic association of the electrolyte and the formation of the abovementioned heteromolecular associates, due to the stronger concentration of the solution and the accumulation of water molecules in the crystalline hydrate.
The solubility of copper(II) nitrate in water at 15 and 45°C is 4.4 and 5.3 M, respectively [5, 895]. Cu(NO3)23H2G crystallohydrate is very soluble in DMSO. We confine ourselves to studying dimethylsulfoxide solutions with concentrations of 2.0 M. The excess and partial molar volumes of the components of the DMSO-Cu(NO3)23H2G system are given in Table 2 and shown in Fig. 2.
Table 2. Excess volumes of the DMSO-Cu(NO3)2-3H2O system (x2 is the molar fraction of cupric nitrate)
X2 -ViE -V2E
0.0013 -0.1200 -0.0704
0.0163 -0.1793 -0.7681
0.0313 -0.3394 -1.2589
0.0462 -0.5955 -1.5442
0.0612 -0.9426 -1.6362
0.0762 -1.3763 -1.5356
0.0912 -1.8917 -1.2471
0.1062 -2.4839 -0.7756
0.1211 -3.1486 -0.1256
0.1361 -3.8804 0.6972
0.1511 -4.6748 1.6888
The partial molar volume of DMSO decreases as the second component is added and curve 1 (Fig. 2) becomes steeper, which can be explained by the transition from one type of the solvent structure to another one. The partial molar volume of Cu(NO3)2 (Fig. 2, curve 2) in the investigated concentration range grows linearly as the content of salt in solution rises, due likely to ionization of the dissolved cupric nitrate followed by ionic association.
o 0.1 0.2
xi
Fig. 2. Partial molar volumes of (1) dimethylsulfoxide and (2) copper(II) nitrate trihydrate as a function of the composition of a solution at 298 K; x2 is a molar fraction of the dissolved substance
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We have demonstrated the good solubility of copper(II) nitrate trihydrate in DMSO at 288-318 K. In diluted solutions, the copper salt is completely ionized. Ion salvation results in the decomposition of the DMSO eigenstructure. Hydrogen bonding between (CH3)2SO molecules and the Н2О molecules in the crystallohydrate results in the formation of heteromolecular associates, the number and importance of which in the rearrangement of the liquid phase structure increase as the concentration of the solution grows.
The properties of low concentration (<0.4 M) solutions are defined mainly by the properties of DMSO. When the temperature rises above 35°Q the structure of the organic solvent decomposes in diluted solutions, the mobility of electrolyte ions increases, and the effect of the solutions' concentration on its optical properties weakens; i.e., the low value of coefficient b in Eq. (1) falls further. In solutions with higher concentrations, the number of heteromolecular associates grows continuously as the salt content in a solution rises, involving the whole system. As a consequence, viscosity increases, ionic association is enhanced, and the effect of concentration on the refraction index of a solution grows.
References
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