# Acoustical Behaviour of Sodium Nitroprusside in Aquo-Organic Solvent Media at 308.15 K

Authors: Monalisa Das; Smrutiprava Das; A. K. Pattanaik
Journal: Journal of Chemistry
 (2013)

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## Abstract

Density and ultrasonic velocity have been measured for sodium nitroprusside in aqueous solutions of CH3OH, ethylene glycol, DMSO, and n-propanol solvents at 308.15 K. A quantitative relationship has been established among the acoustical properties like ultrasonic velocity (U), adiabatic compressibility (β), intermolecular free length (Lf), acoustic impedance (Z), apparent molar compressibility (Kϕ), apparent molar volume (Vϕ), limiting apparent molar compressibility (Kϕ0) limiting apparent molar volume (Vϕ0), and their constants (SK, Sv). From the obtained values, molecular interaction study has been made successfully in the light of these acoustical properties through hydrogen bonding in solute and solvent mixture.


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## Body

## 1. Introduction

In the recent years, ultrasonic velocity measurements are helpful to interpret solute-solvent, ion-solvent, and solvent-solvent interactions in aqueous and nonaqueous medium [1–4]. Recently, acoustic parameter studies of metal complexes have been carried out in our laboratory [5], and A. P. Mishra and D. K. Mishra have also reported a similar work [6]. The interaction helps in better understanding the types of solute and solvent, that is, whether the added solute modifies or distorts the structure of the solvent. Apparent molar volume gives valuable information about ion-ion and ion-solvent interactions in solution [7–11]. The addition of organic solvent to an aqueous solvent of electrolyte brings about a change in ion solvation that results in a large change in the reactivity of dissolved electrolyte [12, 13]. The transition metal plays a vital role in life system because of the natural presence in vitamins, proteins, and enzymes. Sodium nitroprusside (SNP), an Fe (II) ion complex, is an effective drug which rapidly lowers blood pressure and causes vascular smooth muscle relaxation. It is also used in a urine analysis test. In the presence of buffers, it is used as a reagent for ketone strips which test the ketone level in the urine of a diabetic. It is used by forensic chemists in Simons being fast for the identification of illicit substances [14]. Thus, an attempt has been made to elucidate the ion-ion interaction between nitroprusside ions and ion-solvent interaction of SNP in aqueous solutions of methanol, ethylene glycol, n-propanol, and DMSO at 308.15 K through ultrasonic velocity and density measurement.


## 2. Experimental

The entire chemicals used in this present research work are spectroscopic reagents (SRs), analytical reagent (AR) grades of minimum assay of 99.9% obtained from E-Merck, Germany, and SD fine chemicals, India, which are used without further purification. Water used in these experiments was deionized and distilled. A synthetic method of preparation of SNP has been reported [15]. The required quantity of SNP was dissolved in binary mixture of aqueous methanol, ethylene glycol, DMSO, and n-propanol, and a similar procedure has been adopted for different molalities of SNP. The density was determined using a specific gravity bottle by a relative measurement method. The ultrasonic velocity was measured by ultrasonic interferometer having frequency 2 MHz (Mittal Enterprises, model no. F-81). The constant temperature is mentioned by circulatory water through the double wall measuring cell made up of steel.


## 3. Theory

Using the measured data, various acoustic parameters such as adiabatic compressibility, intermolecular free length, acoustic impedance, apparent molar compressibility, apparent molar volume, limiting apparent molar compressibility, limiting apparent molar volume, and the associated constantsSK and SV are calculated.Adiabatic compressibility(β)=1/(U2d).Relative association can be fitted to an equation of the form(1)RA=(dd0)×(U0U)1/3.
Acoustic impedance, Z=U×d.Intermolecular free length can be determined by(2)Lf=Kjβ1/2,
where Kj is Jacobson constant = 2.0965 × 10−6.The apparent molar compressibility,Kϕ, can be computed from
(3)Kϕ=100βm-1-β0d-1(1000m-1-M2).
From the density data, the apparent molar volume Vϕ was calculated from the relation
(4)Vϕ=1000(md0)-1(d0-d)+M2d0-1.
The apparent molar compressibility (Kϕ) and the apparent molar volume (Vϕ) thus obtained are found to vary linearly with m1/2. The Kϕ and Vϕ data were fitted by least squares method
(5)Kϕ=Kϕ0+SKm1/2,Vϕ=Vϕ0+SVm1/2,
where Kϕ0 and Vϕ0 are limiting apparent molar compressibility and limiting apparent molar volume, respectively. SK and SV are the slopes.


## 4. Result and Discussion

The desired parameters such as adiabatic compressibility (β), intermolecular free length (Lf), acoustic impedance (Z), relative association (RA), apparent molar comparability (Kϕ), apparent molar volume (Vϕ), limiting apparent molar compressibility (Kϕ0), limiting apparent molar volume (Vϕ0) and their constants (SK, SV) have been studied at 308.15 K. The density increases with the increase in the concentration of sodium nitroprusside due to the increased electrostriction in the system. The density increases in case of CH3OH + water, ethylene glycol + water, DMSO + water, and n-propanol + water with the increase in the concentration of sodium nitroprusside, but it decreases with mole fraction of CH3OH and n-propanol and increases with the mole fraction of ethylene glycol and DMSO for a particular concentration of sodium nitroprusside. The decrease in density in case of CH3OH + water and n-propanol + water indicates the decrease in ion-solvent interaction or structure-breaking properties of sodium introprusside. But addition of ethylene glycol and DMSO to water has rigidified the three-dimensional structure of water forming a strong hydrogen bond between solvent moleuculs [16, 17]. It also indicates the structure-forming properties of sodium nitroprusside in ethylene glycol + water and DMSO + water.Table1 shows that ultrasonic velocity increases with the increase in the concentration of sodium nitroprusside in aqueous CH3OH and DMSO, but it is found to be decreased in aqueous ethylene glycol and n-propanol. Molecular association is responsible for the observed increase in ultrasonic velocity in these mixtures. The increase in ultrasonic velocity in these solutions may be attributed to the cohesion brought about by the hydration [18].Table 1
The values of density (d), ultrasonic velocity (U), adiabatic compressibility (β), intermolecular free length (Lf), acoustic impedance (Z), and relative association (RA) of sodium nitroprusside in CH3OH + water, ethylene glycol + water, DMSO + water, and n-propanol + water at 308.15 K.
Mole fraction
Concentration (m)
Density (d)
Ultrasonic velocity
Adiabatic compressibility
Intermolecular free length
Acoustic impedance
Relative association
(Xorg)
mol dm−3
(103 kg/m3)
(U) (m/sec)
(β) × 10−7 N−1 m2
(Lf) × 10−13 m
(Z) × 10−3 kg m−2 s−1
(RA)
Sodium nitroprusside + CH3OH + water
0.047
0.01
0.9818
1532.4
4.3374
1.3807
1.5045
0.9824
0.02
0.9827
1534.4
4.3221
1.3783
1.5078
0.9829
0.03
0.9837
1536.6
4.3065
1.3758
1.5115
0.9834
0.04
0.9846
1538.7
4.2897
1.3731
1.5147
0.9838
0.05
0.9855
1540.4
4.2763
1.3710
1.5180
0.9844
0.099
0.01
0.9696
1552.3
4.2801
1.3716
1.5051
0.9660
0.02
0.9705
1553.6
4.2690
1.3698
1.5077
0.9666
0.03
0.9715
1554.8
4.2580
1.3680
1.5104
0.9674
0.04
0.9724
1538.7
4.2470
1.3663
1.5131
0.9680
0.05
0.9733
1540.4
4.2360
1.3645
1.5158
0.9686
0.160
0.01
0.9574
1573.3
4.2203
1.3620
1.5061
0.9496
0.02
0.9583
1573.7
4.2136
1.3609
1.5080
0.9495
0.03
0.9588
1574.3
4.2082
1.3600
1.5094
0.9508
0.04
0.9597
1574.8
4.2016
1.3589
1.5113
0.9516
0.05
0.9602
1575.5
4.1957
1.3580
1.5127
0.9519
0.228
0.01
0.9424
1556.3
4.3810
1.3800
1.4666
0.9381
0.02
0.9433
1555.9
4.3791
1.3875
1.4676
0.9391
0.03
0.9436
1555.6
4.3794
1.3874
1.4678
0.9394
0.04
0.9442
1555.2
4.3789
1.3873
1.4684
0.9401
0.05
0.9452
1554.9
4.3759
1.3868
1.4696
0.9412
0.307
0.01
0.9273
1537.7
4.5608
1.4158
1.4259
0.9268
0.02
0.9276
1536.7
4.5652
1.4165
1.4257
0.9273
0.03
0.9283
1535.6
4.5683
1.4170
1.4254
0.9282
0.04
0.9286
1534.6
4.5728
1.4177
1.4250
0.9287
0.05
0.9292
1533.5
4.5764
1.4183
1.4249
0.9295
Sodium nitroprusside + ethylene glycol + water
0.035
0.01
1.0071
1542.0
4.1760
1.3548
1.5529
1.0056
0.02
1.0081
1541.4
4.1751
1.3547
1.5538
1.0067
0.03
1.0086
1540.8
4.1763
1.3548
1.5540
1.0074
0.04
1.0093
1540.2
4.1766
1.3549
1.5544
1.0082
0.05
1.0099
1539.6
4.1774
1.3550
1.5548
1.0089
0.075
0.01
1.0165
1572.3
3.9794
1.3225
1.5982
1.0184
0.02
1.0175
1571.7
3.9786
1.3224
1.5992
1.0095
0.03
1.0185
1571.0
3.9782
1.3223
1.6000
1.0107
0.04
1.0193
1570.3
3.9786
1.3220
1.6006
1.0116
0.05
1.0203
1569.6
3.9783
1.3198
1.6014
1.0128
0.01
1.0259
1610.8
3.7567
1.2850
1.6525
1.0096
0.02
1.0274
1612.3
3.7443
1.2829
1.6564
1.0107
0.121
0.03
1.0287
1613.7
3.7331
1.2809
1.6600
1.0117
0.04
1.0301
1615.2
3.7211
1.2789
1.6638
1.0182
0.05
1.0315
1617.5
3.7055
1.2762
1.6684
1.0137
0.177
0.01
1.0362
1636.5
3.6035
1.2585
1.6957
1.0143
0.02
1.0381
1637.7
3.5916
1.2564
1.7000
1.0160
0.03
1.0390
1638.8
3.5837
1.2550
1.7027
1.0166
0.04
1.0409
1639.9
3.5724
1.2531
1.7069
1.0192
0.05
1.0419
1641.4
3.5637
1.2515
1.7098
1.0190
0.243
0.01
1.0475
1663.6
3.4494
1.2313
1.7457
1.0198
0.02
1.0494
1664.0
3.4415
1.2299
1.7462
1.0216
0.03
1.0503
1664.4
3.4369
1.2291
1.7481
1.0224
0.04
1.0522
1664.8
3.4291
1.2277
1.7517
1.0241
0.05
1.0541
1665.2
3.4213
1.2263
1.7552
1.0259
Sodium nitroprusside + DMSO + water
0.027
0.01
1.0071
1553.5
4.1144
1.3448
1.5645
1.0031
0.02
1.0087
1554.0
4.1052
1.3433
1.5675
1.0046
0.03
1.0099
1554.4
4.0982
1.3421
1.5697
1.0057
0.04
1.0109
1554.9
4.0915
1.3410
1.5718
1.0065
0.05
1.0137
1555.4
4.0776
1.3387
1.5767
1.0093
0.059
0.01
1.0203
1590.2
3.8759
1.0352
1.6224
1.0084
0.02
1.0212
1591.1
3.8676
1.3038
1.6248
1.0091
0.03
1.0230
1592.0
3.8569
1.3020
1.6286
1.0107
0.04
1.0240
1592.9
3.8488
1.3006
1.6311
1.0115
0.05
1.0259
1593.8
3.8373
1.2987
1.6350
1.0132
0.097
0.01
1.0334
1628.1
3.6506
1.2667
1.6824
1.0133
0.02
1.0344
1628.8
3.6440
1.2656
1.6848
1.0142
0.03
1.0362
1629.6
3.6341
1.2638
1.6886
1.0158
0.04
1.0372
1630.4
3.6270
1.2626
1.6910
1.0166
0.05
1.0381
1631.1
3.6208
1.2615
1.6932
1.0173
0.144
0.01
1.0466
1656.1
3.4837
1.2374
1.7332
1.0205
0.02
1.0475
1657.0
3.4379
1.2293
1.7351
1.0212
0.03
1.0484
1658.0
3.4245
1.2269
1.7382
1.0218
0.04
1.0503
1658.9
3.4179
1.2257
1.7423
1.0235
0.05
1.0512
1659.8
3.4531
1.2320
1.7447
1.0242
0.01
1.0606
1683.3
3.3276
1.2094
1.7853
1.0285
0.02
1.0613
1684.2
3.3218
1.2083
1.7874
1.0290
0.307
0.03
1.0619
1685.0
3.3168
1.2074
1.7893
1.0294
0.04
1.0625
1685.9
3.3114
1.2064
1.7912
1.0298
0.05
1.0634
1686.8
3.3050
1.2053
1.7937
1.0305
Sodium nitroprusside + n-propanol + water
0.206
0.01
0.9893
1681.3
3.5759
1.2537
1.6633
0.9598
0.02
0.9902
1678.8
3.5833
1.2550
1.6623
0.9611
0.03
0.9912
1676.1
3.5912
1.2564
1.6563
0.9626
0.04
0.9921
1661.3
3.6521
1.2670
1.6482
0.9663
0.05
0.9931
1658.1
3.6626
1.2688
1.6467
0.9679
0.057
0.01
0.9715
1627.2
3.8875
1.3071
1.5808
0.9528
0.02
0.9724
1621.4
3.9118
1.3072
1.5766
0.9548
0.03
0.9733
1625.8
3.8870
1.3112
1.5724
0.9549
0.04
0.9743
1609.4
3.9626
1.3197
1.5680
0.9591
0.05
0.9451
1605.3
3.9796
1.3226
1.5653
0.9607
0.094
0.01
0.9546
1573.5
4.2310
1.3637
1.5021
0.9468
0.02
0.9555
1568.5
4.2540
1.3674
1.4987
0.9486
0.03
0.9564
1563.4
4.2778
1.3712
1.4952
0.9506
0.04
0.9578
1558.5
4.2984
1.3745
1.4927
0.9530
0.05
0.9583
1553.0
4.3267
1.3790
1.4882
0.9546
0.138
0.01
0.9367
1517.7
4.6368
1.4246
1.4216
0.9403
0.02
0.9386
1515.3
4.6410
1.4281
1.4223
0.9427
0.03
0.9396
1509.8
4.6689
1.4325
1.4186
0.9448
0.04
0.9405
1504.3
4.6986
1.4371
1.4145
0.9469
0.05
0.9424
1499.6
4.7186
1.4401
1.4132
0.9498
0.194
0.01
0.9198
1464.4
5.0698
1.4928
1.3469
0.9344
0.02
0.9208
1461.1
5.0872
1.4953
1.3454
0.9361
0.03
0.9227
1457.8
5.0997
1.4972
1.3451
0.9381
0.04
0.9245
1457.8
5.1143
1.4993
1.3445
0.9413
0.05
0.9264
1451.0
5.1270
1.5012
1.3442
0.9440
Xorg: mole fractions of the organic cosolvent, corresponding to Xorg, are 10, 20, 30, 40, and 50 v/V%, respectively.The adiabatic compressibility (Table1) decreased with increasing the concentration of solute in all aqueous solvent solutions except n-propanol + water. The decreasing adiabatic compressibility observed for sodium introprusside in CH3OH + water, ethylene glycol + water, and DMSO + water confirms the calculation drawn from the velocity data. The increasing electrostrictive compression of water around the solute molecules results in a large decrease in the compressibility of solutions. The decrease in the compressibility implies that the molecular association is enhanced in these systems with the increase in the solute content as the new entities formed due to molecular association become compact and less compressable [19]. The compressibility appeared to decrease with increasing hydrogen bond strength between solute and solvent molecules. The larger decrease in compressibility of nitroprusside in DMSO + water indicates larger molecular association capacity than other solvents. But the increase of adiabatic compressibility with the increase in concentration of solution may be due to collection of solvent molecules around ion [20] supporting weak ion-solvent interaction. This indicates that there is significant ion-solvent interaction.The intermolecular free length (Lf) is a predominant factor in solvation chemistry. Intermolecular free length depends on the intermolecular attractive and repulsive forces. In the present paper, the intermolecular free length is found to decrease with the increase in the concentration of nitroprusside as shown in Table 1, indicating a significant molecular association between solute and solvent molecules, suggesting a structure-promoting behaviors on addition of solute.The character that determines the restriction/backward movement of sound wave is known as acoustic impendence (Z). It has been estimated for nitroprusside solution of CH3OH + water, ethylene glycol + water, and DMSO + water which is found to increase with the increase in the concentration of sodium nitroprusside. But a reverse trend in the value of Z is observed for sodium nitroprusside solution of n-propanol + water. The higher impedance in DMSO + water indicates the presence of bulkier-solvated ion due to ion-solvent/solvent-solvent interaction which restrict the free flow of ultrasonic velocity.The decrease in relative association (RA) is due to the breaking up of the solvent molecules on adding the solute, whereas the increase as RA may be due to the solvation of solute [21]. In all the systems, RA increases with the increase in the concentration due to the increase in electrostatic attraction. From this data, it can be said that ion-ion interaction between nitroprusside ions overcomes the ion-solvent interaction.The following observations have been made onKϕ and Vϕ of sodium nitroprusside in aqueous CH3OH, ethylene glycol, DMSO, and n-propanol mixtures whose values are given in Table 2. (i)
The values ofKϕ are negative for all the systems over the entire range of concentration.(ii)
The values ofKϕ increase linearly with increasing the ion concentration.(iii)
The values ofVϕ are positive for CH3OH and n-propanol whereas  negative for ethylene glycol and DMSO.Table 2
The data of concentration, apparent molar compressibility (Kϕ), and  apparent molar volume (Vϕ) of sodium nitroprusside in CH3OH + water, ethylene glycol + water, DMSO + water, and n-propanol + water at 308.15 K.
Concentration
Apparent molar compressibility
Apparent molar volume
(m) mol dm−3
−(Kϕ) × 10−3 m2 N−1
(Vϕ) × 10−3 m3 mol−1
Sodium nitroprusside + CH3OH + water
Xorg
0.047
0.099
0.160
0.228
0.307
0.047
0.099
0.160
0.228
0. 307
0.01
0.8895
1.7665
1.8060
2.2354
1.5545
1.2153
1.8549
2.7133
3.4489
4.5363
0.02
0.4551
1.4259
1.3810
1.7833
1.0767
0.8676
1.6813
2.0950
2.9807
3.9907
0.03
0.3113
1.1368
0.9367
1.3445
0.7567
0.6448
1.3115
1.6218
1.9895
2.6502
0.04
0.2424
0.7206
0.6381
0.9238
0.4653
0.5359
1.1053
1.3798
1.5520
2.2165
0.05
0.1329
0.4721
0.3549
0.8459
0.3059
0.4705
0.8742
1.2162
1.2814
1.6033
Sodium nitroprusside + ethylene glycol + water
Xorg
0.035
0.075
0.121
0.117
0.243
0.035
0.075
0.121
0.117
0.243
0.01
2.5035
4.4695
6.6966
8.2255
9.7695
−0.8102
−1.4964
−2.1054
−2.9105
−3.3467
0.02
2.0921
3.4918
5.0941
6.1076
7.8581
−0.4100
−1.1792
−1.5808
−2.3949
−2.7874
0.03
1.5133
2.4726
3.4826
4.8721
6.5100
−0.1901
−0.8122
−1.2352
−1.8191
−2.0885
0.04
0.5252
1.4043
1.6639
3.5932
5.3940
−0.0853
−0.5834
−1.0454
−1.5682
−1.8506
0.05
0.3920
0.7903
1.3359
1.6195
3.1943
−0.0204
−0.4296
−0.8642
−1.2096
−1.4241
Sodium nitroprusside + DMSO + water
Xorg
0.027
0.059
0.097
0.144
0.201
0.027
0.059
0.097
0.144
0.201
0.01
3.1195
4.2045
5.4575
7.1265
8.2988
−1.0192
−1.7471
−2.3732
−3.4993
−3.8276
0.02
1.5396
2.7276
3.8456
4.8761
6.0566
−0.4402
−1.0689
−1.7329
−2.3919
−3.0861
0.03
1.0057
1.8100
2.5527
4.2513
4.8103
−0.2337
−0.6731
−1.1157
−1.5248
−1.9574
0.04
0.5917
1.3447
1.8991
2.4220
2.6882
−0.1255
−0.4550
−0.7870
−1.1165
−1.4233
0.05
0.3122
0.5718
1.5053
1.8407
2.1369
−0.0968
−0.3423
−0.5879
−0.8513
−1.0906
Sodium nitroprusside + n-propanol + water
Xorg
0.026
0.057
0.094
0.138
0.194
0.026
0.057
0.094
0.138
0.194
0.01
5.9045
3.6885
2.5045
1.8966
1.2107
0.7716
2.3623
3.0625
3.4633
4.4763
0.02
4.1491
2.5066
1.7535
1.4344
0.7427
0.4903
1.6857
2.2358
2.7212
3.1981
0.03
3.1457
1.7097
1.5021
0.8798
0.3870
0.3933
1.2993
1.5603
2.0859
2.6904
0.04
1.8364
1.0602
0.6956
0.5131
0.2495
0.3473
0.7949
1.2099
1.6451
2.0475
0.05
1.4217
0.7279
0.4701
0.2432
0.1107
0.2176
0.7012
1.0178
1.3377
1.6597Further, the negative values ofVϕ indicated electrostatic solvation of ions [22]. In other words, the large negative value of Kϕ may  indicate the presence of packing or caging effect [23]. The decrease in the negative value indicates that with the increase in the mole fraction of aquo-organic solvents, ion-solvent interaction increases as the caging effect diminishes.The limiting apparent molar compressibilityKϕ0 provides information regarding ion-solvent interaction. The values of limiting apparent molar compressibility Kϕ0 are negative in all the systems as the shown in Figures 1, 2, 3, and 4. It decreases with the increase the in concentration of sodium nitroprusside solution for ethylene glycol and DMSO systems but increases in case of n-propanol system. The decrease is not regular in CH3OH system. It implies that a little bit ion-ion interaction exists in CH3OH and more ion-ion interaction in n-propanol systems. But the large negative values for ethylene glycol and DMSO systems indicate negligible ion-ion interaction and stronger ion-solvent interaction.Figure 1
Variation of apparent molar compressibility (Kϕ) C1/2 for sodium nitroprusside in different nitroprusside mole fraction of CH3OH in water at 308.15 K. Kϕ0 corresponds to its value at zero concentration.Figure 2
Variation of apparent molar with compressibility (Kϕ) with C1/2 for sodium in different mole fraction of ethylene glycol in water at 308.15 K. Kϕ0 corresponds to its value at zero concentration.Figure 3
Variation of apparent molar compressibility (Kϕ) with C1/2 for sodium nitroprusside in different nitroprusside in different mole fraction of DMSO in water at 308.15 K. Kϕ0 corresponds to its value at zero concentration.Figure 4
Variation of apparent molar compressibility (Kϕ) with C1/2 for sodium nitroprusside in different mole fraction of n-propanol in water at 308.15 K. Kϕ0 corresponds to its value at zero concentration.The volume behavior of solute at infinite dilution is satisfactorily represented byVϕ0 which is independent of ion-ion interaction and provides information concerning ion-solvent interaction. The values of Vϕ0 are positive for CH3OH and n-propanol shown in Figures 5 and 8, whereas these are negative for ethylene glycol and DMSO (Figures 6 and 7).Thus in ethylene glycol and DMSO solutions, predominance of ion-solvent interaction is again proved by negative Kϕ0 and Vϕ0 values. However, in CH3OH and n-propanol solutions, positive values of Vϕ0 suggest that ion-ion interactions predominate.Figure 5
Variation of apparent molar volume (Vϕ) with C1/2 for sodium nitroprusside in different mole fraction of CH3OH in water at 308.15 K. Vϕ0 corresponds to its value at zero concentration.Figure 6
Variation of apparent molar volume (Vϕ) with C1/2 for sodium nitroprusside in different mole fraction of ethylene glycol in water at 308.15 K. Vϕ0 corresponds to its value at zero concentration.Figure 7
Variation of apparent molar volume (Vϕ) with C1/2 for sodium nitroprusside in different mole fraction of DMSO in water at 308.15 K. Vϕ0 corresponds to its value at zero concentration.Figure 8
Variation of apparent molar volume (Vϕ) with C1/2 for sodium nitroprusside in different mole fraction of n-propanol in water at 308.15 K. Vϕ0 corresponds to its value at zero concentration.The constantSK provides information regarding ion-ion interaction. The values of SK (Table 3) exhibit positive in all the systems. These values increase in ethylene glycol and DMSO systems, but this increase is not regular in CH3OH confirming insignificant ion-ion interaction. It decreases in n-propanol system. The value of SK in n-propanol system is higher at low mole fraction, indicating more ion-ion interaction. In case of ethylene glycol and DMSO systems, ion-ion interactions are stronger because of having greater value of SK. So ion-ion interaction is favoured at high mole fraction of ethylene glycol and DMSO, but it is favoured at low mole fraction of n-propanol. The Sv exhibits negative values in CH3OH and n-propanol systems suggesting the presence of more ion-ion interactions and less complex formation occurring in the systems. The values of Sv which exhibit positive from Table 3 in ethylene glycol and DMSO systems reflect the existence of weak ion-ion interactions and predict the complex formation taking place in the systems.Table 3
Results of limiting apparent molar compressibility (Kϕ0), limiting apparent molar volume (Vϕ0), and SK and SV.
Xorg
Limiting apparent molar compressibility
Limiting apparent molar volume
S
K
S
V
(Kϕ0) m2 N−1
(Vϕ0) m3 mol−1
m3 mol−2 kg Pa−1
m3 kg1/2 mol−3/2
Sodium nitroprusside + CH3OH + water
0.047
−0.94
1.1
0.291
−0.123
0.099
−1.86
1.85
0.383
−0.194
0.160
−1.72
2.75
0.404
−0.306
0.228
−2.26
3.5
0.424
−0.384
0.307
−1.58
4.6
0.383
−0.510
Sodium nitroprusside + ethylene glycol + water
0.035
−3.0
−0.9
0.176
0.172
0.075
−4.1
−1.57
0.306
0.268
0.121
−7.4
−2.26
0.424
0.384
0.177
−8.8
−2.98
0.466
0.474
0.243
−10.2
−3.53
0.488
0.577
Sodium nitroprusside + DMSO + water
0.027
−2.9
−0.95
0.249
0.176
0.059
−4.35
−1.8
0.344
0.268
0.097
−5.56
−2.6
0.404
0.364
0.144
−7.25
−3.7
0.488
0.445
0.201
−8.45
−3.85
0 .554
0.532
Sodium nitroprusside + n-propanol + water
0.026
−6.0
0.8
0.554
−0.466
0.057
−3.8
2.3
0.384
−0.404
0.094
−2.8
3.0
0.287
−0.344
0.138
−1.9
3.65
0.213
−0.268
0.194
−1.2
4.4
0.141
−0.105Generally, the types of interactions occurring between sodium nitroprusside and aqueous solutions of solvents can be classified as follows:(i)
ionic-hydrophilic interactions between the ions of sodium nitroprusside and polar group of solvents,(ii)
hydrophilic-hydrophobic interactions between the ions of sodium nitroprusside and the nonpolar side group of solvents.


## 5. Conclusion

In summary, volume and compressibility data have been determined for sodium nitroprusside in aqueous CH3OH, ethylene glycol, DMSO, and n-propanol at 308.15 K, and the results have been used to study the ion-solvent interactions present in the mixtures. From the magnitude of Kϕ0. Vϕ0, SK and SV, it can be concluded that a larger ion-solvent interaction will exist in ethylene glycol and DMSO solvents than other solvents. Thus, sodium nitroprusside is an effective structure maker in aqueous ethylene glycol and DMSO solutions over other two systems.



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*Source: 942430-2012-11-07.xml*