Conductivity in MnSO4–saccharide–water solutions at 298.15 K

Fluid Phase Equilibria 352 (2013) 28–33

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Conductivity in MnSO4 –saccharide–water solutions at 298.15 K Jing Zhao, Yujuan Chen, Yaohui Liu, Kelei Zhuo ∗ School of Chemistry and Chemical Engineering, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Normal University, Xinxiang, Henan 453007, People’s Republic of China

a r t i c l e

i n f o

Article history: Received 21 January 2013 Received in revised form 4 May 2013 Accepted 6 May 2013 Available online 21 May 2013 Keywords: Manganese sulfate d-Glucose d-Galactose d-Fructose Conductivity

a b s t r a c t Conductivities for MnSO4 –saccharide (d-glucose, d-galactose and d-fructose)–water solutions were measured, together with densities, viscosities of the aqueous saccharide solutions at 298.15 K. According to the Lee–Wheaton conductivity equation, limiting molar conductivities 0 and association constants KA were obtained. The Walden products (0 0 ) were also calculated. These parameters have been interpreted in terms of ion–ion and ion–solvent interactions in aqueous saccharide solutions. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Carbohydrates are the most abundant organic molecules on earth [1], which hold a key position in living nature and have received a huge interest over the past few decades because of their abilities to preserve biosystems such as cells, vaccines, or therapeutic proteins employed in the food, pharmaceuticals, and cosmetics industries [2]. The abundance of electronegative functional groups and a well-defined stereochemistry make saccharides potentially interesting ligands for the binding of metal ions in natural systems, and the understanding of such interactions remains one of the main challenges of carbohydrate chemistry [3]. In addition, many interesting functions of sugar chains have also been elucidated by recent studies [4–6]. And carbohydrates also are subjected to chemical reaction for the development of new polymeric materials [7], and an increasing effort has been devoted to find ways to use them as feedstocks for production of organic chemicals [8]. Moreover, their solution properties are of considerable interest for various aspects of basic research and in many applications as well [9–11]. Electrolytic solutions are of fundamental importance to chemistry and biology as they form a basic matrix for technological fluids and the evolution and function of life. Transition metal ions in living organisms are found to properly coordinate with different biomolecules, and to participate in many biochemical reactions where they play a crucial role [12]. Manganese is found in all body tissues as it is essential for many ubiquitous enzymatic reactions,

∗ Corresponding author. Tel.: +86 373 3329056; fax: +86 373 3329056. E-mail addresses: [email protected], [email protected] (K. Zhuo). 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.05.006

including synthesis of amino acids, lipids, proteins, and carbohydrates [13]. Interactions between metal ions and polyalcohols, nucleosides, nucleotides, and other sugar-type ligands are supposed to be involved in many biochemical processes in living organisms, including recognition processes, immunological events, and pathological conditions [14]. Therefore, the studies on the interaction between saccharides and Manganese ions, being an important branch of bioinorganic chemistry, provide an accessible route to enhance our understanding on the chemical/biological nature of carbohydrate molecules [15]. In addition, the effect of electrolytes on the thermophysical properties of carbohydrates systems is of special interest, which are useful to saccharide chemical industry, the treatment of wastewater containing saccharides, separation and purification processes of biomaterials [16–18], metabolic processes of organisms [19,20] and examining the characteristics of saccharids in body fluids and osmotic agents [21]. The transport properties (conductance, viscosity, and transference numbers) of such systems are important because they can provide useful and sensitive information about ion-solvent interaction, ion–ion association, and solvent structure. Moreover, electrical conductivity data can provide information about the density of free ions and their mobility [22]. Studies of the transport properties of electrolytes in different solvent media are of considerable importance for the behavior of ions in solution [23]. However, only few investigations on the conductivity of polyvalent electrolyte in aqueous nonelectrolyte (saccharide) solutions are reported in the literature. In our previous work [24,25], systematic and precise measurements of conductivities for NiSO4 –glucose–water solutions at 278.15–308.15 K and for 1-alkyl-3-methylimidazolium chloride

J. Zhao et al. / Fluid Phase Equilibria 352 (2013) 28–33 Table 1 Purities and sources of the samples used in this work. Chemical

Source

Purity (mass%)

d-Glucose d-Galactose d-Fructose MnSO4 ·6H2 O EDTA

Sigma Sigma Sigma Alfa Beijing Chem. Co.

>99.0% >99.0% >99.0% >99.97% >99.0%

29

suspended level Ubbelohde viscometer, which was placed in a water thermostat (Schott, Mainz, Germany), with a flow time of about 200 s for water at 298.15 K. Details of the experimental procedure including calibrating process were given elsewhere [29]. Densities and viscosities of saccharide–water mixtures at 298.15 K are listed in Table 2. 2.3. Conductivity measurements

ionic liquids–monosaccharide–water solutions at 298.15 K were reported. With the aim of carrying out a systematic investigation, in the present work, the conductivities of MnSO4 in aqueous saccharide (d-glucose, d-galactose, d-fructose) solutions were measured at 298.15 K. The limiting molar conductivities (0 ), association constants (KA ), and Walden products (0 0 ) were derived. 2. Experimental 2.1. Materials The chemicals used in this work are described in Table 1. The studied saccharides were dried under vacuum at room temperature to constant weight, and then stored over P2 O5 in desiccators. MnSO4 ·6H2 O was dissolved in pure distilled deionized water, and its molarity was determined by titration with EDTA. Water with a conductivity of 1.0–1.2 × 10−4 S m−1 was used throughout the experiments under an argon atmosphere to avoid taking up carbon dioxide. Saccharide–water mixed solvents (mS = 0.2000, 0.4000, 0.6000, 0.8000, 1.0000 and 1.2000 mol kg−1 , subscript S represents saccharide and mS is the molality defined as moles of saccharide per kilogram of water) were prepared by weighing, permitting storage and transfer of the solvent into the measuring cell under a argon atmosphere. Six ternary stock solutions (MnSO4 –saccharide–water) were prepared by adding a weighed amount of aqueous MnSO4 solution with a fixed concentration and a weighed amount of saccharide to a flask. The preparation work is done very carefully to be sure that the values of mS in these as prepared ternary solutions equals accurately to those in the corresponding binary saccharide–water solutions.

A conductivity meter (Model 145A+, Thermo Orion) and a conductivity cell (Model 013016D, Thermo Orion) were used for measurements of conductivity. The Conductance cell was equipped with a water-circulating jacket, and the temperature fluctuation was controlled within 0.02 K. The cell constant was calibrated by adding potassium chloride solutions consecutively [30]. All data were corrected at 298.15 K with the conductivity of the corresponding solvent. At the beginning of every measuring cycle, the cell was filled with a weighed amount of solvent. To minimize the risk of the presence of concentration gradients in the cell, the solution was continuously stirred with a magnetic stirrer. After the measurement of the solvent conductivity, the stepwise concentration was carried out by successive additions, using a gastight syringe, of weighed amounts of electrolytic solution (with or without saccharide). The relative uncertainty of conductivity was estimated to be less than 0.5%. 3. Data analysis The densities, viscosities, and dielectric constants for water–saccharide mixtures are also reported in Table 2, and molar conductivities of ½MnSO4 in water–saccharide mixtures are collected in Table 3. The experimental data were analyzed using the Lee–Wheaton [31–33] conductivity equation in the form suggested by Pethybridge and Taba [34,35].



=

2

3

0 [1 + C1 (ˇ) + C2 (ˇ) + C3 (ˇ) ]

−



R  2 1 + C4 (ˇ) + C5 (ˇ) + 12 (1 + R)

1−

2.2. Density and viscosity measurements

KA =

Solution densities were measured with a vibrating-tube digital densimeter (model DMA 60/602, Anton Paar, Austria), as described elsewhere [26–28]. Solution viscosities were measured by a

f±2 = exp −

 (1)

(2)

c 2 f±2 ˇ 1 + R

(3)

Table 2 Densities, dielectric constants, and viscosities for saccharide (d-glucose, d-galactose and d-fructose) + water mixtures at 298.15 K and 1 atm. mS /mol kg−1 0.2000

0.4000

0.6000

0.8000

1.0000

1.2000

1.04506 75.4 1.272

1.05663 74.8 1.395

1.06819 74.0 1.528

1.04800 76.2 1.268

1.05936 75.2 1.384

1.07022 75 1.511

1.04776 75.6 1.252

1.05908 75 1.362

1.06991 74.4 1.483

d-glucose

d/g cm−3 εa /mPa s

1.01037 77.8 0.975

1.02193 76.9 1.066

1.03350 76.2 1.166

d/g cm−3 εa /mPa s

1.01067 78.1 0.973

1.02368 77.4 1.062

1.03612 76.8 1.160

d/g cm−3 εa /mPa s

1.01062 77.8 0.969

1.02358 77 1.055

1.03594 76.3 1.150

d-galactose

d-fructose

Standard uncertainties u are u(T) = 0.01 K, u(p) = 5 kPa, and u(mS ) = 0.0004 mol kg−1 . The combined expanded uncertainty Uc is Uc (d) = 1.0 × 10−5 kg dm−3 , and the relative combined expanded uncertainty Uc % is Uc () % = 0.25% (0.95 level of confidence). a Taken from Ref. [46].

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J. Zhao et al. / Fluid Phase Equilibria 352 (2013) 28–33

Table 3 Molar conductivity  for ½MnSO4 in saccharide (d-glucose, d-galactose and d-fructose) + water mixtures at 298.15 K and 1 atm. 104 c/mol dm−3

/S cm2 mol−1

mS = 0.2000 mol kg−1 0.9683 2.1709 3.0781 3.9353 4.9562 6.0705 7.2263 mS = 0.8000 mol kg−1 1.0604 2.2745 3.4500 4.7996 6.2007 7.5889 8.8512

116.6 113.1 111.1 109.4 107.8 106.2 104.6 91.5 88.5 86.3 84.4 82.6 81.0 79.8

mS = 0.2000 mol kg−1 1.1913 2.0433 2.8272 3.6509 4.4521 5.2803 6.0663 6.8339 7.6945 8.6354 mS = 0.8000 mol kg−1 0.9430 1.9829 2.9415 4.1797 5.0248 6.2597 7.3878 8.4328 9.6143 10.9705

117.6 115.2 113.2 111.4 110.0 108.5 107.3 106.1 105.0 103.9 93.3 90.6 88.5 86.4 85.1 83.5 82.3 81.2 80.1 78.9

mS = 0.2000 mol kg−1 0.8784 1.7289 2.5831 3.3845 4.1045 4.7895 5.8086 6.5829 7.4602 8.5103 mS = 0.8000 mol kg−1 1.0044 2.3425 3.4392 4.4969 5.5635 6.3567 7.2269 8.4287 9.5679 10.9354

119.2 116.4 114.0 112.3 110.8 109.8 108.2 107.0 105.8 104.4 94.4 90.8 88.7 86.9 85.4 84.3 83.1 81.8 80.7 79.6

104 c/mol dm−3

/S cm2 mol−1

104 c/mol dm−3

Water–d-glucose mS = 0.4000 mol kg−1 1.0707 105.8 2.1603 103.2 3.1522 100.9 4.1561 98.9 5.1189 97.3 6.2320 95.6 7.4206 94.2 mS = 1.0000 mol kg−1 1.1792 83.6 2.2580 81.3 3.3931 79.4 4.6285 77.5 6.1996 75.8 7.9762 74.1 9.6873 72.6

mS = 0.6000 mol kg−1 1.0329 2.9503 3.9162 4.7711 5.7415 6.7806 8.2669 mS = 1.2000 mol kg−1 1.2720 2.7125 4.0083 5.3920 6.9410 8.7032 10.6500

Water–d-galactose mS = 0.4000 mol kg−1 0.8061 110.3 1.8939 106.8 2.8898 104.4 3.8663 102.6 4.5082 101.4 5.2837 100.2 6.3194 98.7 7.2241 97.5 8.2028 96.2 9.3976 94.9 mS = 1.0000 mol kg−1 0.9891 86.2 2.1455 83.4 3.1520 81.4 4.2580 79.6 5.4170 78.1 6.6116 76.7 7.5786 75.7 8.8664 74.4 10.3303 73.2 11.5300 72.3

mS = 0.6000 mol kg−1 1.0139 1.9413 2.8511 3.8560 4.8174 5.7225 6.6239 7.5907 8.7936 10.0861 mS = 1.2000 mol kg−1 1.6036 2.6692 3.7537 4.8374 6.7124 7.7152 8.8583 9.8463 11.0175 12.3275

Water–d-fructose mS = 0.4000 mol kg−1 0.9140 110.0 1.9472 106.1 2.8539 104.1 3.7529 102.4 4.4154 101.2 5.3891 99.8 6.3755 98.4 7.2361 97.3 8.1339 96.3 9.2480 95.0 mS = 1.0000 mol kg−1 1.0602 87.2 2.2653 84.2 3.4501 82.0 4.4644 80.3 5.6225 78.7 77.4 6.8059 7.8567 76.2 9.0463 75.1 10.3944 73.9 12.0478 72.6

mS = 0.6000 mol kg−1 1.0173 1.9505 2.8743 3.8143 4.8131 5.7955 6.7230 7.7740 8.9057 10.1393 mS = 1.2000 mol kg−1 1.0059 2.3671 3.9207 5.1583 6.3360 7.7714 8.8733 10.2934 11.5855 13.3051

/S cm2 mol−1

98.7 94.2 92.5 91.1 89.8 88.7 87.0 77.0 74.0 72.0 70.2 68.7 67.3 66.0

100.7 98.1 96.1 94.2 92.6 91.3 90.1 89.0 87.6 86.3 78.0 75.8 74.1 72.7 70.5 69.5 68.6 67.7 66.9 66.0

101.6 98.8 96.8 95.0 93.4 91.8 90.6 89.4 88.1 86.9 80.6 77.4 74.8 73.2 71.9 70.4 69.3 68.2 67.3 66.1

Standard uncertainties u are u(T) = 0.01 K, u(p) = 5 kPa, and u(mS ) = 0.0004 mol kg−1 . The relative combined expanded uncertainty Uc % is Uc () % = 0.25% (0.95 level of confidence). c is the molarity, moles of MnSO4 in 1 dm−3 of ternary mixture; mS is the water-molality, moles of saccharide in 1 kg of water.

ˇ = |z± |2

 =

e2 ε0 εkB T

8NA2 |z± |2 c 1000ε0 εkB T

e 299.79 × 3

(4)

 = F|z± |

(5)

where C1 –C5 are complex functions of R, KA is the association constant,  is the Debye parameter,  is the degree of dissociation, c the electrolyte concentration, f± is the mean ion activity

1/2

(6)

J. Zhao et al. / Fluid Phase Equilibria 352 (2013) 28–33

a = a+ + a−

(7)

Using the ionic radii of Mn2+ and SO4 2− [36], we have a = 0.349 nm for MnSO4 . From extended investigations on electrolyte solutions in amphiprotic hydroxylic solvents (water, alcohols), it is known that the upper limit of association is given by an expression of the type [36]. R = a + ns

(8)

where s is the length of an oriented solvent molecule, n is an integer, n = 0, 1, 2,. . .. In this work, s is the length of an OH-group, dOH , and s = dOH = 0.28 nm. Here, dOH is the length of an oriented water molecule between anion and cation in a solvent separated ion pair [M2+ (H2 O)n X2− ] [33,37]. The length of the oriented water molecule is referred to the distance between two hydrogen-bonded oxygen atoms in water [38]. For solutions of 2:2 electrolyte MnSO4 we can fix the distance parameter R at R = a + 2s = 0.909 nm or R = a + 1s = 0.629 nm. Similar assumption was made for some 2:2 electrolytes in the literature [39,40]. The limiting molar conductivity 0 and the association constant KA obtained by fitting at R = 0.909 nm and R = 0.629 nm are summarized in Table 4. Results show that the 0 and KA values

130

D-glucose D-galactose D-fructose

110

2

-1

/(S cm mol )

120

0

100

v

coefficient of the dissociated species (the activity coefficient of the non-conducting species was assumed to be equal to 1), e is the electronic charge, z± is the ionic charge, ε0 is the permittivity of vacuum, ε is the dielectric constant of the solvent,  is the viscosity of the solvent, and the other symbols have their usual meanings. The parameter R represents the center-to-center distance between the ions in the ion pairs. At separations beyond this distance, the ions are considered to be unassociated. Three-parameter fits can be used to obtain limiting values 0 of the molar conductivity, the association constant KA and the distance parameter R by non-linear least squares iterations. The values of R obtained by three-parameter fit sometimes diverge much from the theoretical values. Whereas R has specific physical meaning, and its theoretical value can be evaluated from the length of ion pair, a three-parameter evaluation has been replaced by a twoparameter procedure by setting R to its theoretical value. An initial value of KA was presumed in order to calculate the mean ionic activity coefficients f± , and then the calculated values of f± were used to fit other parameters including 0 by the origin soft. Iteration processes were continued until constant KA and 0 values. The lower limit a of the association integral is the distance of the closest approach of cation to anion (contact distance).

31

90

80

0.2

0.4

0.6

0.8

1.0

1.2

-1

mS /(mol kg ) Fig. 1. Variation in the limiting molar conductivity 0 for ½MnSO4 with the molalities of saccharide (d-glucose, d-galactose and d-fructose) at 298.15 K.

at R = 0.909 nm have a small difference from those at R = 0.629 nm (see Table 4), and similar cases were also observed for CoSO4 , NiSO4 , CuSO4 and ZnSO4 in water [40]. And the variation trends of the 0 and KA values obtained at R = 0.909 nm are consistent with those at R = 0.629 nm. Therefore, we select the values obtained by fitting at R = 0.909 nm as the resulting values to be discussed below. 4. Results and discussion 4.1. Molar conductivities  and limiting molar conductivities 0 Molar conductivities  for ½MnSO4 decrease with increasing its concentration for given aqueous saccharide solutions (see Table 3). This behavior can be ascribed to the fact that with the increase of concentration of electrolyte, the interactions between ions strengthen and result in a decrease in anions and cations mobility. Fig. 1 shows that at 298.15 K, limiting molar conductivities 0 for ½MnSO4 decrease with increasing mS . This can be explained based on the fact that with the increasing mS , the interactions of ions with saccharides strengthen, the microscopic viscosity of the mixtures increase (see Table 2), and hence the mobility

Table 4 Limiting molar conductivity 0 for ½MnSO4 and association constant KA for MnSO4 in saccharide (d-glucose, d-galactose and d-fructose) + water mixtures at 298.15 K. Saccharide

mS /mol kg−1 0.2000

d-Glucose d-Galactose d-Fructose

122.7 122.0 124.9 125.2

± ± ± ±

0.4000 0.1 0.1a 0.1 0.1

112.3 110.3 115.8 115.4

± ± ± ±

0.6000 0.2 0.1a 0.1 0.2

d-Glucose d-Glactose d-Fuctose

174 ± 2 199 ± 2 194 ± 3

212 ± 8 213 ± 3 209 ± 5

d-Gucose d-Glactose d-Fuctose

122.7 ± 0.1 125.0 ± 0.1 125.3 ± 0.1

112.4 ± 0.2 115.8 ± 0.1 115.5 ± 0.2

d-Glucose d-Galactose d-Fructose

165 ± 2 190 ± 2 184 ± 3

203 ± 8 204 ± 3 200 ± 5

a

Taken from Ref. [25].

0.8000

0 /S cm2 mol−1 (R/nm = 0.909) 104.3 ± 0.1 97.0 ± 0.1 101.9 ± 0.1a 95.9 ± 0.1a 106.6 ± 0.1 98.6 ± 0.1 107.6 ± 0.1 100.2 ± 0.1 KA /dm3 mol−1 (R/nm = 0.909) 201 ± 3 222 ± 3 224 ± 3 235 ± 2 232 ± 3 254 ± 4 0 /S cm2 mol−1 (R/nm = 0.629) 104.3 ± 0.1 97.1 ± 0.1 106.6 ± 0.1 98.6 ± 0.1 107.7 ± 0.1 100.3 ± 0.1 KA /dm3 mol−1 (R/nm = 0.629) 191 ± 3 212 ± 3 215 ± 3 225 ± 2 222 ± 3 244 ± 4

1.0000 89.1 87.8 91.4 92.8

± ± ± ±

1.2000 0.1 0.1a 0.1 0.1

82.3 82.5 84.4 85.7

± ± ± ±

0.1 0.1a 0.1 0.1

222 ± 3 251 ± 3 262 ± 4

243 ± 4 260 ± 3 269 ± 4

89.1 ± 0.1 91.4 ± 0.1 92.8 ± 0.1

82.3 ± 0.1 84.4 ± 0.1 85.7 ± 0.1

211 ± 3 240 ± 3 251 ± 3

233 ± 5 249 ± 3 258 ± 4

J. Zhao et al. / Fluid Phase Equilibria 352 (2013) 28–33 Table 5 Walden product (0 0 ) for ½MnSO4 in saccharide + water mixtures at 298.15 K. Saccharide

mS /mol kg−1 0.2000

d-Glucose d-Galactose d-Fructose

0.8000

1.0000

1.2000

0 0 (½MnSO4 )/S cm2 mol−1 mPa s 119.61 119.69 121.62 123.41 121.47 122.93 123.69 125.00 121.31 121.74 123.70 125.43

0.4000

0.6000

124.27 126.46 126.40

125.73 127.52 127.09

128

D-glucose D-galactose D-fructose

126

-1

2

124

122

v

0

0

of ions decreases. And the limiting molar conductivities for ½MnSO4 at a given mS are in the order except for fructose at mS = 0.4 mol kg−1 : fructose > galactose > glucose. Since the partial molar compressibilities for aqueous saccharides are in the order: glucose > galactose > fructose [41], the hydration abilities are also in this order. The viscosities for the saccharide–water mixed solvents also are the same as the above-mentioned order (see Table 2). The solvents with larger viscosity hinder more strongly the ionic mobility of MnSO4 . This further shows that small stereo-structure difference between these hexoses can result in the difference in conductivity. For the sake of comparison, values of 0 for NiSO4 also are given in Table 4. For a given glucose + water solution, the limiting molar conductivities of electrolytes are in the order: MnSO4 > NiSO4 , indicating that the hydrated radii are in the order: Ni2+ > Mn2+ . Both Mn2+ and Ni2+ have two net positive charges, but they have different ionic radii (a+ = 0.091 and 0.067 nm for Mn2+ and Ni2+ respectively) [36]. Compared with Mn2+ , the smaller Ni2+ ion has a higher surface charge density, and thus associates more water molecules to form a larger hydrated ion. Therefore, the hydrated Ni2+ ion has smaller conductivity.

/(S cm mol mPa s )

32

4.2. Thermodynamics of the ion-association process

120

Fig. 2 shows that the association constants (KA ), except for glucose at mS = 0.4 mol kg−1 , increase with increasing saccharide molality. With decreasing dielectric constant of the mixed solvent, the electrostatic attraction between cations and anions increases, and the association degree increases, and consequently the values of KA increase with increasing saccharide molality. The association degree of MnSO4 is larger in fructose–water and galactose–water solutions than in glucose–water solution, indicating that the interactions of fructose and galactose with the electrolytes are stronger than those of glucose. 4.3. The Walden product Values of the Walden product (0 0 ) were also calculated and are included in Table 5. An increase in viscosity leads to a decrease in conductivity. This effect was formulated quantitatively by the Walden rule [42], which stated that the product 0 0 should be approximately constant for a given electrolyte, irrespective of the nature of the solvent, provided that the radius of the ion remains unchanged. As shown in Fig. 3, the absolute values of the Walden

D-glucose D-galactose D-fructose

260

0.5

1.0

1.5

-1

mS /(mol kg ) Fig. 3. Variation in the Walden products 0 0 for ½MnSO4 with the molalities ms of saccharide (d-glucose, d-galactose and d-fructose).

product (0 0 ) increase slowly with increasing mS . According to the uncertainties in the experimental viscosity and conductivity, it can be reasonably expected that some experimental points will deviate from the linear relation, but this does not influence the increasing tendency. This suggests that these ions have different effective radii in different solvent compositions, and consequently provides an evidence for the solvation of the ions in the solutions. Similar phenomena have been observed in other mixtures of water with organic cosolvents [43,44]. This behavior seems to be caused by the preferential solvation of ions by water molecules. In turn, it verifies that the change in the microscopic viscosity related to the addition of saccharide is smaller than the change in the macroscopic viscosity (the so-called “sorting effect” [45]). Furthermore, with increasing mS , the interactions of ions with saccharides are stronger, radii of the solvated ions become larger, and thus ion mobilities become smaller. In addition, the deviation of the Walden product in saccharide–water systems from that in water is in the order galactose/fructose > glucose. This indicates that the interactions of galactose and fructose with the electrolyte are stronger than those of glucose.

3

-1

KA /(dm mol )

240

0.0

5. Conclusions

220

200

180

0.0

0.5

1.0

1.5

-1

mS /(mol kg ) Fig. 2. Variation in the association constants KA for MnSO4 with the molalities of saccharide (d-glucose, d-galactose and d-fructose).

The conductivities of MnSO4 in aqueous saccharide (glucose, galactose and fructose) solutions were measured. The limiting molar conductivities (0 ), association constants (KA ), and Walden products (0 0 ) were calculated. The 0 values were found to decrease with increasing saccharide molality. At given molalities of the saccharides, the 0 values fellow the order: fructose > galactose > glucose. This can be attributed to the fact that the viscosities for saccharide–water mixed solvent have the opposite order. The KA values were found to increase with increasing saccharide molality, indicating that these saccharides can promote the association of MnSO4 in Aqueous solutions. The 0 0 values

J. Zhao et al. / Fluid Phase Equilibria 352 (2013) 28–33

increase with increasing saccharide molality for MnSO4 , indicating the preferential solvation of the ions by water molecules. List of symbols

f± c e T n z R NA kB F mS KA

mean ion activity coefficient concentration (mol dm−3 ) electronic charge thermodynamic temperature hydration number ion charge distance parameter of Eq. (1) Avagadro’s number (6.022045 × 1023 mol−1 ) Boltzmann constant (1.3806503 × 10−23 J K−1 ) Faraday constant (96,485.309 c mol−1 ) molality of saccharide (mol kg−1 ) association constant

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