Article pubs.acs.org/jced
Effects of Alkaline Earth Metal Ions on Thermodynamic and Ultrasonic Properties of Ascorbic Acid Shashi Kant† and Sunil Kumar*,‡ †
Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla-171005, India School of Chemistry, Faculty of Basic Sciences, Shoolini University, Solan-173229, India
‡
ABSTRACT: The density (ρ) and sound speed (u) has been measured for ascorbic acid ((5R)-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran2(5H)-one) + H2O + magnesium chloride (MgCl2) (or calcium chloride (CaCl2), or barium chloride (BaCl2)) at temperatures T = (303.15, 308.15, 313.15, and 318.15) K and atmospheric pressure p = 0.1 MPa. These parameters were then used to obtain thermodynamic and acoustic functions such as apparent molar volume (ϕv), limiting apparent molar volume (ϕov ), limiting apparent molar volume expansibility (ϕoE), adiabatic compressibility (κs), intermolecular free length (Lf) and relaxation time (τ). The ion−solvent and ion−ion interactions in ascorbic acid + H2O system have been discussed using these parameters. The effect of MgCl2, CaCl2, and BaCl2 on these interactions as well as on the solvent structure has also been discussed.
1. INTRODUCTION The ion−solvent and ion−ion interactions in solutions are useful to understand behavior of solute in that solvent and vice versa. Apparent molar volume, adiabatic compressibility, and other acoustic parameters can be employed to obtain various types of interactions in the solutions. The nature of these interactions is further useful to explain structural changes occurring in the solutions. Similar interactions have been reported recently1−5 for carbohydrates, amino acids, and proteins. The interactions of Mg2+, Ca2+, and Ba2+ ions in ascorbic acid + water have been investigated in this work. Ascorbic acid has importance as vitamin C and is also used in photography, fluorescence microscopy, and food-technology. Magnesium ions are necessary for nucleic acids and also find applications in paper, textiles, and cement industry. Calcium builds and maintains bones and is used in wastewater treatment. Barium is employed in pigment manufacture, steel hardening, and is an efficient muscle stimulant. The present work involves density, molar volume, and sound speed measurements for the solutions of MgCl2, CaCl2, and BaCl2, taking 0.01 mol·kg−1 of ascorbic acid in water as solvent as shown in Scheme 1. These measurements have been carried
2. EXPERIMENTAL SECTION 2.1. Chemicals Used. Ascorbic acid, magnesium chloride, calcium chloride, and barium chloride used for this study were of analytical grade supplied by Sigma-Aldrich. All these chemicals were used as supplied without any further purification. Water has been used as the primary solvent obtained from series of distillations till its specific conductance attains the range of 0.1·10−6 to 1.0·10−6 Ω−1·cm−1. The purity of water was further checked by measuring its density. The uncertainties in the temperature and measured density were ± 0.05 K and ± 2.7·10−5 g·cm−3, respectively, and even after their consideration, the purity of water was found to be in close proximity with the literature values6 as shown in Table 1. The information regarding used chemicals as quoted by the supplier is also given in Table 1. Before use the chemicals were kept in a vacuum oven to eliminate any moisture. 2.2. Preparation of Solutions. All the solutions were prepared by mass using an analytical balance (precision 1·10−5 g) supplied by Dhona Instruments Pvt. Ltd. Ascorbic acid in water and all solutions in aqueous ascorbic acid were prepared at 303.15 K, taking material losses due to vaporization at this temperature to be insignificant. Seven concentrations ranging from 0.01 mol·kg−1 to 0.12 mol·kg−1 of MgCl2, CaCl2, and BaCl2 were prepared taking 0.01 mol·kg−1 of ascorbic acid in water as solvent for all studies. 2.3. Instrumentation. DSA (Density and Sound Analyzer) 5000 supplied by Anton Paar, GmbH, Garz, Austria was used for the measurement of densities and sound velocities. These studies were carried out at atmospheric pressure p = 0.1 MPa
Scheme 1. 3D Representation of Solvent
out at four different temperatures T = (303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure p = 0.1 MPa to obtain ion−solvent and ion−ion interactions for the studied systems. © 2013 American Chemical Society
Received: January 22, 2013 Accepted: March 18, 2013 Published: April 1, 2013 1294
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3. RESULTS AND DISCUSSION 3.1. Molar Volume Studies. Densities of solution (ρ) and solvent (ρ0) were used to obtain the apparent molar volume7−8 (ϕv) of the solute at particular temperature by the expression
Table 1. Physical Properties of the Solvents and Salts Used −3
solvent water water + ascorbic acid (0.01 mol·kg−1)
ρ/(g·cm ), 303.15 K
lit. value , 303.15 K
0.995674 0.996272
0.995647
6
ϕv = (M 2 /ρ) − 1000(ρ − ρ0 )/mρρ0
as reported by the supplier salt
melting point, Tm/K
magnesium chloride calcium chloride barium chloride ascorbic acid
987.15 1045.15 1236.15 463.15
where M2 is the molecular weight of electrolyte. Obtained data of ϕov for MgCl2, CaCl2, and BaCl2 taking 0.01 mol·kg−1 of ascorbic acid as solvent is reported in Table 2. Errors associated with ρ and ρ0 in ϕov were calculated using the expression
mass fraction purity ≥ ≥ ≥ ≥
(1)
0.98 0.99 0.99 0.99
Δϕv = (2Δρ /ρ2 )(1000/m + M 2)
and four different temperatures T = (303.15, 308.15, 313.15 and 318.15) K with an accuracy of ± 0.05 K. The uncertainty in density and speed of sound measurements were ± 3.2·10−5 g·cm−3 and ± 0.9 m·s−1, respectively.
(2)
The errors were estimated to range from ± 0.08 cm−3·mol−1 at solute concentrations of 0.01 mol·kg−1 to ± 0.18 cm−3·mol−1 at solute concentrations of 0.12 mol·kg−1.
Table 2. Experimental Density ρ, Apparent Molar Volume ϕv and Sound Speed u at Molality m for the System Ascorbic Acid (1) + Water (2) + MgCl2 (3) (or CaCl2 (3) or BaCl2 (3)) at Temperatures T = (303.15, 308.15, 313.15 and 318.15) K and Pressure p = 0.1 MPaa ρ/g·cm−3 m/mol·kg
−1
MgCl2
CaCl2
ϕv/cm3·mol−1 BaCl2
MgCl2
u/m·s−1
CaCl2
BaCl2
MgCl2
CaCl2
BaCl2
120.75 121.26 121.89 122.56 122.99 123.43 123.84 T/K = 308.15
52.11 52.41 52.87 53.36 53.60 53.89 54.10
56.89 57.53 58.62 59.34 60.04 60.65 61.26
1509.00 1510.78 1511.96 1514.12 1516.37 1518.57 1520.74 1522.72
1509.00 1511.46 1512.07 1513.83 1515.96 1516.61 1519.71 1521.60
1509.00 1510.66 1511.27 1512.43 1513.59 1514.64 1515.72 1516.79
121.32 121.77 122.38 122.91 123.22 123.68 124.01 T/K = 313.15
52.64 52.95 53.38 53.69 54.01 54.22 54.44
59.90 60.35 61.16 61.98 62.38 62.81 63.27
1520.58 1521.35 1522.64 1524.68 1526.91 1529.04 1531.11 1533.10
1520.58 1522.19 1522.88 1524.44 1526.56 1527.08 1530.25 1532.15
1520.58 1521.40 1521.90 1523.05 1524.08 1525.08 1526.05 1527.01
121.79 122.20 122.82 123.40 123.72 124.04 124.25 T/K = 318.15
53.18 53.48 53.86 54.12 54.36 54.58 54.76
61.80 62.44 63.05 63.49 63.82 64.17 64.52
1529.61 1530.42 1531.73 1533.66 1535.86 1537.97 1539.99 1541.89
1529.61 1531.36 1532.09 1533.53 1535.59 1535.87 1539.27 1541.19
1529.61 1530.54 1530.95 1532.14 1533.03 1534.05 1534.92 1535.74
122.18 122.64 123.18 123.62 123.98 124.28 124.57
53.60 53.85 54.24 54.52 54.76 54.99 55.15
63.48 63.82 64.23 64.63 64.91 65.17 65.45
1537.13 1537.99 1539.32 1541.22 1543.36 1545.40 1547.43 1549.28
1537.13 1539.04 1539.79 1541.12 1543.14 1544.10 1546.80 1548.71
1537.13 1538.20 1538.48 1539.74 1540.53 1541.50 1542.34 1543.02
T/K = 303.15 0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
0.996272 0.997098 0.997912 0.999519 1.001091 1.002648 1.004179 1.005688
0.996272 0.997219 0.998159 1.000024 1.001865 1.003702 1.005521 1.007333
0.996272 0.998140 0.999993 1.003662 1.007301 1.010904 1.014479 1.018021
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
0.994643 0.995464 0.996274 0.997873 0.999445 1.001006 1.002532 1.004048
0.994643 0.995584 0.996518 0.998372 1.000212 1.002035 1.003853 1.005656
0.994643 0.996479 0.998304 1.001924 1.005502 1.009072 1.012614 1.016126
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
0.992814 0.993631 0.994438 0.996030 0.997592 0.999144 1.000676 1.002200
0.992814 0.993749 0.994677 0.996521 0.998353 1.000173 1.001981 1.003781
0.992814 0.994629 0.996429 1.000011 1.003570 1.007111 1.010628 1.014122
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
0.990800 0.991614 0.992417 0.994005 0.995570 0.997116 0.998647 1.000159
0.990800 0.991730 0.992654 0.994489 0.996311 0.998121 0.999919 1.001712
0.990800 0.992596 0.994383 0.997941 1.001474 1.004992 1.008491 1.011969
m is the molality of MgCl2 (or CaCl2 or BaCl2) in 0.01 mol·kg−1 (ascorbic acid + water) solvent. Standard uncertainties U are U(T) = 0.05 K, U(ρ) = 0.000032 g·cm−1 and U(u) = 0.9 m·s−1. a
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The ϕov is a measure of solute−solvent or ion−solvent interactions.14 Appreciable ion−solvent interactions for MgCl2, CaCl2, and BaCl2 in the studied solvent were confirmed by the positive values of ϕov . With increase in temperature the ϕov values for MgCl2, CaCl2, and BaCl2 were found to increase (Figure 2) suggesting more solvation of ions due to decrease in
The ϕov data for various concentrations of magnesium chloride, calcium chloride, and barium chloride taken in 0.01 mol·kg−1 of ascorbic acid as solvent was analyzed using Masson’s equation10 to obtain limiting apparent molar volume as ϕv = ϕvo + Sv m
(3)
where ϕov is the limiting apparent molar volume, Sv is the experimental slope, and m is the molality of the solution. ϕv varies linearly with √m (Figure 1) and linear fitting was used to
Figure 2. Limiting apparent molar volume ϕov as a function of temperature T in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at pressure p = 0.1 MPa: ■, MgCl2; ●, CaCl2; ▲, BaCl2.
hydrogen bonding among solvent molecules, thus increasing availability of free solvent molecules for the solvation of ions (Scheme 3).
ϕov
Figure 1. Apparent molar volume as a function of square root of molal concentration √m in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at temperature T = 303.15 K and pressure p = 0.1 MPa: ■, MgCl2; ◆, CaCl2; ▲, BaCl2.
Scheme 3. Array of Molecular Interactions
obtain intercept (ϕov ) and slope (Sv). The data for limiting apparent molar volume (ϕov ) and slopes (Sv) along with standard errors are presented in Table 4 and graphically in Scheme 2. The slope Sv in Masson’s equation is a measure of Scheme 2. Array of Limiting Apparent Molar Volumes
The dependence of ϕov on temperature for MgCl2, CaCl2, and BaCl2 in the studied solvent follows the polynomial: ϕvo = a0 + a1T + a 2T 2
(4)
over the temperature range T = (303.15, 308.15, 313.15 and 318.15) K. a0, a1, and a2 are the constants and depend upon the nature of electrolyte and the solvent. The coefficients of eq 4 for the studied electrolytes have been reported in Table 3. The limiting apparent molar volume expansibilities defined as ϕoE = (∂ϕov /∂T)p were also calculated for MgCl2, CaCl2, and BaCl2 in 0.01 mol·kg−1 of ascorbic acid in water by following relation
ion−ion or solute−solute interactions.11−13 Low and positive values of Sv for MgCl2, CaCl2, and BaCl2 were obtained, suggesting weak ion−ion interactions. With an increase in temperature there is a decrease in ion−ion interactions for these metal chlorides in the studied solvent system which is possibly due to more solvation of ions at higher temperature.
ϕEo = a1 + 2a 2T
(5)
and are reported in Table 4. The standard errors in the ϕoE determination are ± 9.93·10−3, ± 8.60·10−3 and ± 9.93·10−3 for 1296
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κs was further employed to obtain intermolecular free length21 (Lf) using eq 8
Table 3. Values of Various Coefficients (a0, a1, and a2) of eq 4 for the System Ascorbic Acid (1) + Water (2) electrolyte
a0/cm3·mol−1
a1/cm3·mol−1·K−1
a2/cm3·mol−1·K−2
MgCl2 CaCl2 BaCl2
−206.36 −223.92 −1607.02
1.98 1.67 10.21
− 0.0030 − 0.0025 − 0.0156
Lf = Kκs1/2
where K is a temperature dependent constant22 (= (93.875 + 0.375 T)·10−8). Lf decreases with an increase in mol·kg−1 of the electrolyte and increases with an increase in temperature23−25 (Table 5). The relative association26 (RA) was also calculated using eq 9 to obtain a firm impact of interactions occurring in solutions.
Table 4. Limiting Apparent Molar Volume ϕ0v , Experimental Slopes SV, and Apparent Molar Volume Expansibility ϕ0E for the System Ascorbic Acid (1) + Water (2) + MgCl2 (3) (or CaCl2 (3) or BaCl2 (3)) at Temperatures T = (303.15, 308.15, 313.15, and 318.15) K and Pressure p = 0.1 MPa T/K
ϕ0v /cm3·mol−1
303.15 308.15 313.15 318.15
119.45 120.22 120.78 121.24
(±0.054) (±0.046) (±0.068) (±0.023)
303.15 308.15 313.15 318.15
51.26 51.91 52.56 52.96
(±0.045) (±0.017) (±0.019) (±0.012)
303.15 308.15 313.15 318.15
55.06 58.45 60.85 62.68
(±0.050) (±0.088) (±0.089) (±0.028)
Sv/cm3·kg1/2·mol‑3/2 MgCl2 0.127 0.110 0.104 0.098 CaCl2 0.083 0.074 0.064 0.064 BaCl2 0.178 0.140 0.107 0.080
RA = (ρ /ρ0 )(u 0 /u)1/3
0.168 0.138 0.108 0.078
(±0.002) (±0.001) (±0.001) (±0.001)
0.143 0.117 0.092 0.067
(±0.002) (±0.004) (±0.004) (±0.001)
0.756 0.600 0.444 0.288
MgCl2, CaCl2, and BaCl2, respectively. The values of ϕoE were found to decrease with increase in temperature (Table 4) for MgCl2, CaCl2, and BaCl2 indicating the absence of the caging effect15−17 for these electrolytes in the experimental solutions. The structure making/breaking behavior of MgCl2, CaCl2, and BaCl2 in 0.01 mol·kg−1 of ascorbic acid in water was interpreted by the sign of (∂2ϕvo/∂T2)p as suggested by Hepler18 using the thermodynamic expression ⎛ ∂ 2ϕ0 ⎞ ⎛ ∂C̅ 0 ⎞ P ⎟ = −T ⎜⎜ 2v ⎟⎟ ⎜ ⎝ ∂P ⎠T ⎝ ∂T ⎠ P
0
Z = uρ
(10)
R = (M /ρ)u1/3
(11)
W = (M /ρ)κs−1/7
(12)
M represents the apparent molecular weight of the solution and was calculated as M = M1W1 + M 2W2
(13)
W1 and W2 are weight fractions and M1 and M2 are molecular weights of solvent and solute, respectively. Z increases with increases with temperature as well as molality of electrolyte (Figure 4) suggesting the presence of solvent−solute interactions in the system. R and W were increasing linearly with electrolyte molality (Figures 5 and 6) indicating the solute−solvent interactions in the system.31 Another parameter studied was solvation number32,33 (Sn), obtained by eq 14
(6)
(C̅ 0P)
relating partial molar heat capacity at infinite dilution with ϕov . Equation 6, suggests that (∂2ϕov /∂T2)p will have a positive value for a structure maker electrolyte and negative value for a structure breaker electrolyte. For MgCl2, CaCl2, and BaCl2 negative values of (∂2ϕov /∂T2)p have been obtained suggesting the structure-breaker nature of MgCl2, CaCl2, and BaCl2 in experimental solutions. 3.2. Ultrasonic Studies. The speed of sound (u) and density (ρ) (Table 1) were used to obtain various acoustic parameters for MgCl2, CaCl2, and BaCl2 taking 0.01 mol·kg−1 of ascorbic acid in water as solvent. The theoretical definition of adiabatic compressibility, κs = (−1/Vm)( ∂Vm/∂P)S cannot be used for the determination of κs so it has been obtained by the Newton−Laplace equation19 7, κs = 1/u 2ρ
(9)
where ρ represents solvent density and u is the speed of sound in the solvent. RA is dependent upon the breaking-up of aggregated solvent molecules on the addition of solute and the solvation of solute molecules. The first parameter causes a decrease in RA and the second leads to an increase in RA. In the present study an increase in RA has been observed with an increase in temperature as well as with an increase in concentration (Figure 3), suggesting the presence of ion− solvent interactions27 in the system. Specific acoustic impedance (Z), Rao’s molar sound function (R), and molar compressibility (W) were also obtained for the studied system using eqs28−30 10, 11, and 12: 0
ϕ0E/cm3·mol−1K−1
(±0.002) (±0.002) (±0.003) (±0.001)
(8)
S N = (n1/n2)(1 − κs/κs 0)
(14)
Where n1 and n2 are the numbers of moles of the solvent and the solute and κs and κs0 are compressibility coefficients of the solution and the pure solvent. Considerably high solvation numbers (Table 5) obtained especially at low solute concentrations and at low temperatures indicate either strong electrostriction around the chloride ions and/or cation electrostrictive interaction exceeding the first solvation shell.34 This is not surprising because in the acoustic method outer shell molecules also get compressed in addition to the inner ones resulting in high solvation numbers. The dispersion of ultrasonic waves in the system contains information about the characteristic time of relaxation process that causes the dispersion. The relaxation time35−38 (τ) was calculated as
(7)
Adiabatic compressibility was found to decrease with an increase in mol·kg−1 of the electrolyte (Table 5) attributed to formation of additional incompressible solvation shells of the electrolyte molecules in the solvent.20
τ = (4η /3ρu 2) 1297
(15)
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Table 5. Adiabatic Compressibility κs, Inter Molecular Free Length Lf, Solvation Number SN, and Relaxation Time τ at Molality m for the System Ascorbic Acid (1) + Water (2) + MgCl2 (3) (or CaCl2 (3) or BaCl2 (3)) at Temperatures T = (303.15, 308.15, 313.15 and 318.15) K and Pressure p = 0.1 MPaa m/mol·kg−1
κs·10‑10/m2·N−1
Lf·10‑11/m
SN
τ·10‑13/s
m/mol·kg−1
κs·10‑10/m2·N−1
Magnesium Chloride
a
4.4080 4.3940 4.3836 4.3640 4.3443 4.3250 4.3060 4.2884
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3483 4.3403 4.3294 4.3109 4.2916 4.2729 4.2549 4.2374
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3050 4.2969 4.2861 4.2684 4.2496 4.2313 4.2138 4.1970
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.2716 4.2633 4.2525 4.2353 4.2169 4.1993 4.1818 4.1655
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.4080 4.3895 4.3818 4.3635 4.3433 4.3316 4.3061 4.2877
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3483 4.3350 4.3270 4.3101 4.2902 4.2795 4.2541 4.2359
SN
τ·10‑13/s
4.3772 4.3731 4.3649 4.3551 4.3503 4.3368 4.3275 T/K = 318.15
17.8772 14.1490 12.2124 12.2754 10.7004 11.9513 11.8946
3.7936 3.8045 3.8171 3.8219 3.8343 3.8290 3.8303
4.3985 4.3943 4.3864 4.3767 4.3700 4.3585 4.3492 Barium Chloride T/K = 303.15
18.9476 14.7359 12.2884 12.2608 11.2851 11.9091 11.8468
3.4411 3.4489 3.4591 3.4648 3.4719 3.4717 3.4724
4.3488 4.3431 4.3318 4.3206 4.3099 4.2993 4.2888 T/K = 308.15
22.5415 18.6142 16.4466 15.6591 15.1150 14.7743 14.5097
4.7202 4.7295 4.7391 4.7385 4.7427 4.7387 4.7354
4.3608 4.3554 4.3442 4.3335 4.3230 4.3127 4.3025 T/K = 313.15
16.1864 14.9619 14.5386 14.1792 13.9416 13.7428 13.5750
4.2156 4.2242 4.2303 4.2338 4.2349 4.2352 4.2330
4.3776 4.3725 4.3613 4.3510 4.3404 4.3304 4.3207 T/K = 318.15
16.8482 14.8970 14.5229 13.9841 13.7936 13.5407 13.3174
3.7888 3.7958 3.8022 3.8065 3.8075 3.8091 3.8093
4.3990 4.3942 4.3828 4.3728 4.3624 4.3524 4.3430
17.7366 14.8408 14.5864 13.8859 13.6613 13.4056 13.1177
3.4409 3.4475 3.4523 3.4563 3.4581 3.4603 3.4607
Calcium Chloride
T/K = 303.15 0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
Lf·10‑11/m
T/K = 313.15
4.3508 4.3456 4.3359 4.3261 4.3165 4.3070 4.2982 T/K = 308.15
17.6469 15.3885 13.8367 13.3715 13.0651 12.8315 12.5422
4.7390 4.7565 4.7805 4.7925 4.8031 4.8122 4.8219
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3050 4.2911 4.2830 4.2671 4.2478 4.2385 4.2122 4.1942
4.3631 4.3577 4.3484 4.3386 4.3292 4.3200 4.3112 T/K = 313.15
10.1834 12.0273 11.9123 12.0541 12.0099 11.9082 11.7781
4.2232 4.2356 4.2525 4.2665 4.2762 4.2863 4.2948
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.2716 4.2570 4.2489 4.2338 4.2150 4.2021 4.1799 4.1621
4.3802 4.3746 4.3656 4.3560 4.3466 4.3376 4.3289 T/K = 318.15
10.4258 12.1884 11.7679 11.9005 11.8623 11.7516 11.5937
3.7918 3.8013 3.8175 3.8295 3.8412 3.8526 3.8609
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.4080 4.3901 4.3784 4.3557 4.3334 4.3119 4.2906 4.2697
4.4017 4.3962 4.3872 4.3777 4.3685 4.3595 4.3510 Calcium Chloride T/K = 303.15
10.7497 12.3918 11.7976 11.8420 11.7458 11.6602 11.4793
3.4424 3.4493 3.4638 3.4744 3.4857 3.4951 3.5044
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3483 4.3356 4.3248 4.3027 4.2816 4.2608 4.2405 4.2205
4.3485 4.3447 4.3356 4.3256 4.3198 4.3070 4.2978 T/K = 308.15
23.2911 16.4721 14.0042 13.5828 12.0219 12.8209 12.6154
4.7342 4.7527 4.7718 4.7797 4.7931 4.7886 4.7895
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.3050 4.2919 4.2819 4.2599 4.2399 4.2193 4.1999 4.1809
4.3605 4.3565 4.3480 4.3379 4.3325 4.3196 4.3104
16.9589 13.5735 12.1668 12.3356 10.9613 12.0130 11.9405
4.2247 4.2376 4.2537 4.2602 4.2724 4.2663 4.2703
0.00 0.01 0.02 0.04 0.06 0.08 0.10 0.12
4.2716 4.2580 4.2488 4.2267 4.2075 4.1875 4.1684 4.1504
m is the molality of MgCl2 (or CaCl2 or BaCl2) in 0.01 mol·kg−1 (ascorbic acid + water) solvent. Standard uncertainties U are U(Ks) = 0.0054· 10−10 m2·N1−, U(Lf) = 0.027·10−11 m and U(τ) = 0.0072·10−13 s. 1298
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Figure 3. Relative association RA as a function of molal concentration m in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at temperature T = 303.15 K and pressure p = 0.1 MPa: ■, MgCl2; ◆, CaCl2; ▲, BaCl2.
Figure 6. Molar compressibility W as a function of molal concentration m in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at temperature T = 303.15 K and pressure p = 0.1 MPa: ■, MgCl2; ◆, CaCl2; ▲, BaCl2.
in temperature and increases with increase in electrolyte molality.
4. CONCLUSION It has been found that 0.01 mol·kg−1 of ascorbic acid in water behaves as a solvent similar to water. The positive values of ϕov , decrease in κs, increase in Lf, and increase in RA showing presence of ion−solvent interactions of MgCl2, CaCl2, and BaCl2 with 0.01 mol·kg−1 of ascorbic acid in water as solvent. Acoustic parameters as specific acoustic impedance, Rao’s molar sound function, molar compressibility, solvation number, and characteristic time of relaxation were reported. The decrease in ϕoE values with increase in temperature shows the absence of the “caging effect”, the negative sign of (∂2ϕov /∂T2)p suggests that MgCl2, CaCl2, and BaCl2 act as a structurebreaker in 0.01 mol·kg−1 of ascorbic acid in water as solvent.
Figure 4. Specific acoustic impedance Z as a function of molal concentration m in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at temperature T = 303.15 K and pressure p = 0.1 MPa: ■, MgCl2; ◆, CaCl2; ▲, BaCl2.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: sunil678kumar@rediffmail.com, Tel./Fax: +91 177 2830944. Notes
The authors declare no competing financial interest.
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REFERENCES
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Figure 5. Rao’s molar sound function R as a function of molal concentration m in 0.01 mol·kg−1 ascorbic acid (1) + water (2) system at temperature T = 303.15 K and pressure p = 0.1 MPa: ■, MgCl2; ◆, CaCl2; ▲, BaCl2.
where η is viscosity. (The viscosity data used for calculations is available with the authors.) τ decreases with increase 1299
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NOTE ADDED AFTER ASAP PUBLICATION This paper was published on April 1, 2013 with an incorrect heading in Table 5. The corrected version was reposted on April 3, 2013.
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