Evaluation of Apparent and Partial Molar Volume of Potassium Ferro- and Ferricyanides in Aqueous Alcohol Solutions at Different Temperatures

Indian Journal of Chemical Technology Vol. 11, September 2004, pp. 714-718

Evaluation of apparent and partial molar volume of potassium ferro- and ferricyanides in aqueous alcohol solutions at different temperatures

U N Dasha, G S Royb* & S Mohantyc aDepartment of Chemistry, Utkal University, Bhubaneswar 751 004, India bDepartment of Physics, Rajadhani College, Bhubaneswar, India cDepartment of Physics, S V M College, Jagatsinghpur 754 103, India Received 19 September 2003; revised received 20 May 2004; accepted 16 June 2004

Apparent and partial molar volume of potassium ferro- and ferricyanides in aqueous alcohol solutions have been determined at four different temperatures 298.15, 303.15, 308.15 and 313.15K with the objective of studying ion-solvent interaction in these systems. The transfer of volumes for the transfer of these salts from aqueous alcohol solution to water has been evaluated. Negative transfer of volume was observed and the results have been explained on the basis of electrostriction. IPC Code: G01 N 9/00, C01 C 3/12 Keywords: Apparent molar volume, partial molar volume, potassium ferrocyanide, apparent molar expansibility, aqueous alcohol.

Evaluation of partial molar quantities are of expansibility ΦE are computed by the following importance as they give a lot of informations relations2, regarding ion-solvent interaction in various complex -1 -1 compounds. But since these quantities are not directly ΦV= 1000 (d0 c ) (d0- d ) + M2 d0 … (1) -1 experimentally determined it is difficult to throw light and ΦΕ = α 0Φ V + (α − α 0) 1000 c … (2) on molecular interaction in ternary mixtures. Further, these quantities are related to the corresponding where c is the molar concentration, d0 and d are the apparent molar quantities which are directly densities of solvent and solution respectively, M2 is experimentally determined and can be used for the molecular weight of the solute, α 0 and α are the studying ion-solvent interaction in solution. co-efficients of thermal expansion of solvent and The partial and apparent molar properties of solution respectively. 2 potassium ferro and ferricyanides in water and The Φ V and ΦΕ data are fitted to Masson equation water+acetone mixtures have been reported earlier1. by least squares method, The same properties of these salts in water + methanol, water + ethanol and water + n-propanol 0 1/2 Φ V = Φ V +S V c … (3) mixtures (5, 10 and 20 wt% in each case) at four 0 1/2 and ΦΕ = ΦΕ + SΕ c … (4) different temperatures: 298.15, 303.15, 308.15 and 313.15 K are reported here. Further, the transfer of 0 to obtain ΦV , the limiting apparent molar volume, SV volumes for the transfer of these salts from aqueous the experimental slope of Eq.(3), Φ 0, the limiting alcohol solution to water have also been determined. Ε apparent molar expansibility and S , the experimental The contributions of change in temperature, change in Ε slope of Eq.(4). composition and increase of chain length have been The partial molar volume and partial molar discussed in the light of electrostriction. 3 expansibility have been calculated from the relations ,

Theory V = Φ + (1000 - cΦ ) (2000 + S c3/2)-1 S c1/2… (5) The apparent molar volume ΦV and apparent molar 2 V V V V 3/2 -1 1/2 and E =ΦΕ + (1000 - cΦΕ) (2000 + SΕ c ) SΕ c ______2 *For correspondence. … (6) DASH et al.: EVALUATION OF MOLAR VOLUME OF POTASSIUM FERRO AND FERRICYANIDES 715

The apparent molar volume at infinite dilution, also called the limiting apparent molar volume is equal to 0 the partial molar volume at infinite dilution V2 . The partial molar volume of transfer of the above mentioned salts from aqueous alcohol solution to water are calculated from the relation,

0 0 0 Φ V (tr) = Φ V (aqueous alcohol) - Φ V (water) … (7)

Experimental Procedure Potassium ferrocyanide and potassium ferricyanide (BDH, Anal Rs) were kept over anhydrous calcium chloride in vacuum desiccator until required. Methanol, ethanol and n-propanol (BDH, Anal Rs.) were dried over 4A molecular sieve and distilled. Fig. 1⎯Φ ~ c1/2 for potassium ferrocyanide in 5wt% methanol at -6 -1 V Conductivity water (sp.cand.~10 S cm ) was used (1) 298.15 K, (2) 303.15 K, (3) 308.15 K, (4) 313.15 K and in (5) for preparing water + alcohol mixtures. The alcohol 10 wt% methanol and (6) 20 wt% methanol at 298.15 K. content in the mixed solvents was accurate to within ±0.01% . The solutions were prepared on molal basis and conversion of molarity was done by using standard expression4. The densities were measured pychnometrically (uncertainty ± 1×10-2 kg m-3). Temperature was maintained by a thermostat with a precision of ± 0.05 K.

Results and Discussion 0 A perusal of Table 1 and Fig. 1 shows that, ΦV values of ferrocyanide salt are positive in water and increases with temperature in all the solvents. With increase of alcohol concentration, the value decreases and becomes negative at certain composition. 0 Negative value of ΦV provides evidence of 5 0 electrostriction . Again, since ΦV is a measure of ion- solvent interaction, the negative value indicates 1/2 weaker ion-solvent interaction. The result indicates, Fig. 2⎯ΦE ~ c for potassium ferricyanide in (1) 5 wt% that, the ion-solvent interaction increases with methanol, (2) 10 wt% methanol, (3) 20 wt% methanol, (4) 20 wt% temperature, decreases with alcohol concentration and ethanol and (5) 20 wt% n-propanol at 298.15 K. number of -CH2- groups in alcohol (i.e. chain length). 0 The lowering of ΦV values is probably due to the As observed, SV values are high and positive at increased steric hindrance of the bulkier solvent every temperature and decrease with temperature for molecules to the ion-solvent interaction. The presence both the salts. Since, SV is a measure of ion-ion of ion-solvent interaction between the molecules interaction, the result indicates the presence of ion-ion promotes the structure making effect of the salts in interaction in the system at every temperature and water + alcohol mixtures. In case of ferricyanide salt both the salts ionize to a greater extent with increase 0 (Table 2, Fig. 2), ΦV values are positive in all the in temperature. Ion-ion interaction increases with solvents and at all the four temperatures. Ion-solvent increase of alcohol content in the solution. This interaction of ferricyanide salt is greater than that of suggests that more and more solute molecules are ferrocyanide salt which implies that ferrocyanide salt accommodated within the void spaces left in the shows more structure making effect than ferricyanide packing of the large associated solvent molecules and salt. as such enhance the structure of the solvent. 716 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2004

0 3 -1 9/2 -3/2 0 3 -1 0 3 -1 -1 9/2 -3/2 -1 Table 1⎯Values of ΦV (m mol ), SV (m mol ), ΦV (tr) (m mol ), ΦE (m mol K ) and SE (m mol K ) for potassium ferrocyanide in water and water+alcohol system at different temperatures

wt. % alcohol Temp (K) 106 × Φ 0 109 × S 105 × Φ 0(tr) 106 × Φ 0 -109 × S V V V E E

0.0 298.15 43.6 380.59 - 7.72 18.52 303.15 101.8 205.36 - 7.75 18.59 308.15 133.8 150.84 - 7.79 18.69 313.15 158.9 119.38 - 7.81 18.71 5 (methanol) 298.15 56.6 87.33 1.30 1.54 4.83 303.15 67.3 48.90 -3.45 1.57 4.99 308.15 73.4 31.85 -6.04 1.58 4.99 313.15 80.3 14.96 -7.86 1.59 5.01 10 (methanol) 298.15 15.1 167.02 -2.85 2.53 6.26 303.15 32.3 120.87 -6.95 2.55 6.36 308.15 47.8 79.03 -8.60 2.56 6.32 313.15 52.6 76.11 -10.63 2.58 6.40 20 (methanol) 298.15 -14.3 358.48 -5.79 2.02 6.29 303.15 -7.4 338.48 -10.92 2.04 6.43 308.15 2.5 311.37 -13.13 2.05 6.36 313.15 16.7 261.62 -14.22 2.06 6.41 5 (ethanol) 298.15 47.5 111.85 0.39 1.27 4.70 303.15 54.4 87.91 -4.74 1.26 4.57 308.15 60.8 64.42 -7.30 1.26 4.57 313.15 67.0 38.49 -9.19 1.28 4.64 10 (ethanol) 298.15 31.9 150.20 -1.17 1.50 5.79 303.15 39.2 126.10 -6.26 1.52 5.85 308.15 46.3 97.50 -8.75 1.54 5.94 313.15 55.2 60.30 -10.37 1.56 6.01 20 (ethanol) 298.15 -39.6 481.44 -8.32 5.86 24.50 303.15 -14.6 391.74 -11.64 5.89 24.60 308.15 18.1 246.84 -11.57 5.95 24.90 313.15 48.5 114.48 -11.04 6.04 25.40 5 (n-propanol) 298.15 17.1 267.49 -2.65 1.97 3.31 303.15 24.9 261.62 -7.69 1.99 3.36 308.15 34.6 250.06 -9.92 2.02 3.46 313.15 47.9 213.88 -11.10 2.05 3.54 10 (n-propanol) 298.15 4.6 275.16 -3.90 2.08 3.49 303.15 12.3 271.01 -8.95 2.09 3.49 308.15 25.6 252.65 -10.82 2.12 3.56 313.15 35.1 226.87 -12.38 2.13 3.56 20 (n-propanol) 298.15 -46.5 434.54 -9.01 4.85 1.37 303.15 -25.6 386.28 -12.74 4.87 1.38 308.15 -0.2 304.79 -13.40 4.92 1.40 313.15 27.3 228.51 -13.16 4.98 1.41

molecules and this interaction increases with It is observed that the partial molar volume V2 increases with concentration and temperature in all temperature and decreases with alcohol concentration. 0 the solvents whereas decreases with increase of The values of ΦV (tr) are negative for both the alcohol content in the mixed solvent. Increase of V2 salts. The measured partial molar volume can be with concentration is owing to the structure breaking considered to be a sum of the geometric volume of the of the solvent molecules in concentrated solutions of solute and changes in the solvent due to its interaction high charge density ions like potassium characterized with solvent. This simple approach has been widely by very strong interaction forces with the solvent used in many models6 to interpret partial molar DASH et al.: EVALUATION OF MOLAR VOLUME OF POTASSIUM FERRO AND FERRICYANIDES 717

0 3 -1 9/2 -3/2 0 3 -1 0 3 -1 -1 9/2 -3/2 -1 Table 2⎯Values of ΦV (m mol ), Sv(m mol ), ΦV (tr) (m mol ), ΦE (m mol K ) and SE (m mol K ) for potassium ferricyanide in water and water+alcohol system at different temperatures.

6 0 9 5 0 6 0 9 wt. % alcohol Temp (K) 10 × ΦV 10 × SV 10 × ΦV (tr) 10 × ΦE -10 × SE

0.0 298.15 104.1 23.58 - 4.21 7.81 303.15 131.9 148.11 - 4.24 7.91 308.15 151.7 131.64 - 4.27 7.95 313.15 168.6 107.06 - 4.28 7.98 5 (methanol) 298.15 99.2 178.27 -0.49 2.07 7.26 303.15 104.7 158.92 -2.72 2.10 7.51 308.15 119.9 103.26 -3.18 2.13 7.53 313.15 129.2 73.63 -3.94 2.13 7.49 10 (methanol) 298.15 83.5 182.69 -2.06 2.14 6.32 303.15 90.3 169.32 -4.16 2.16 6.52 308.15 103.0 125.21 -4.87 2.16 6.37 313.15 114.9 94.68 -5.37 2.17 6.40 20 (methanol) 298.15 71.5 190.83 -3.26 2.60 7.10 303.15 75.7 188.21 -5.62 2.64 7.39 308.15 95.0 129.56 -5.67 2.65 7.24 313.15 107.8 98.26 -6.08 2.67 7.28 5 (ethanol) 298.15 80.3 252.67 -2.38 3.45 12.94 303.15 110.8 134.01 -2.11 3.48 13.05 308.15 125.1 77.81 -2.66 3.52 13.23 313.15 133.9 51.37 -3.47 3.54 13.31 10 (ethanol) 298.15 73.4 241.68 -3.07 3.09 11.72 303.15 93.9 157.87 -3.80 3.13 11.89 308.15 107.5 108.55 -4.42 3.17 12.09 313.15 121.3 59.14 -4.73 3.25 12.50 20 (ethanol) 298.15 51.9 292.23 -5.22 2.79 11.20 303.15 71.9 209.08 -6.00 2.81 11.33 308.15 85.4 151.55 -6.63 2.83 11.40 313.15 94.9 121.07 -7.37 2.87 11.59 5 (n-propanol) 298.15 89.7 88.22 -1.44 1.81 2.89 303.15 95.7 88.10 -3.62 1.83 2.94 308.15 107.7 59.53 -4.40 1.83 2.88 313.15 116.5 46.20 -5.21 1.86 2.97 10 (n-propanol) 298.15 78.1 128.29 -2.60 2.40 5.33 303.15 92.4 94.69 -3.95 2.41 5.34 308.15 104.6 62.69 -4.71 2.45 5.47 313.15 114.1 50.97 -5.45 2.49 5.45 20 (n-propanol) 298.15 32.6 353.16 -7.15 3.68 8.54 303.15 49.7 318.98 -8.22 3.69 8.53 308.15 69.9 270.41 -8.18 3.73 8.64 313.15 87.9 227.95 -8.07 3.77 8.76 volume data for a broad range of solutes. When two increase of electrostrictive solvation as well as charged centres are not separated by the distance 3-4 hydrophobic solvation. Hydrophobic solvation A°, then their hydration co-spheres overlap which increases as the number of -CH2- group increases in results in the decrease in the electrostriction. The the alcohols. overlap of co-spheres of two ionic species shows an As expected, the partial molar expansibility E2 increase in volume whereas overlap of hydrophobic- decreases with concentration and increases with 0 hydrophobic and ion-hydrophobic groups results in temperature. The value of ΦΕ increases with decrease in volume. In the present case there is temperature indicating the presence of caging or 718 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2004

8 0 3 Dash U N & Nayak S K, Thermochim Acta, 32 (1979) 331; packing effect . As is seen, the ΦΕ values increase with increase of alcohol content in the mixed solvent. 34 (1979) 165. 4 Robinson R A & Stokes R H, Electrolyte Solutions (Butter This suggests that the structure making effect of the Worths Scientific Publications, London), 1955, 30. electrolytes studied is favoured in aqueous alcohol 5 Davis C W, Ion Association (Butter Worths Scientific medium as compared to aqueous medium. Publication, London), 1962, 154. 6 Rohankar P G & Aswar A S, Indian J Chem, 41A (2002) References 312. 1 Dash U N, Roy G S & Mohanty S, J T R Chem, 9(1) (2002) 7 Chalikian T V, Sarvzyam A P & Breslauer K J, J Phys 55. Chem, 97 (1993) 13017 2 Harned H S & Owen B B, The Physical Chemistry of 8 Millero F J, Structure and Transport Processes in Water and Electrolytic Solutions, 3rd Edn (Reinhold Publishing Aqueous Solutions, Ch.15 edited by Horne R A (Wiley Corporation, New York), 1958, 358. Interscience, New York), 1971.