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Conductance of caesium iodide, ammonium chloride, ammonium bromide and potassium sulphocyanide in dimethyl sulphoxide
Electroanalytical Chemistry and lnterfacial Electrochemistry, 57 (1974) 117-120 © Elsevier Sequoia S.A., Lausanne Printed in The Netherlands
117
SHORT COMMUNICATION
Conductance of caesium iodide, ammonium chloride, ammonium bromide and potassium sulphocyanide in dimethyl sulphoxide R. L. B L O K H R A and M. L. PARMAR
Chemistry Department, Himachal Pradesh University, The Manse Building, Simla-171001 (lndia) (Received 2nd April 1974)
Introduction
Conductance has been the subject of study for the last fifteen to twenty years. During this period Fuoss and his co-workers 1~ have suggested a number of theories to explain the variation of conductance of electrolytic solutions with concentrations. Conductance data were collected for various types of salts in solvents of low to high dielectric constant s 8. Quite recently studies of conductance of DMSO solutions of salts of various types have been summarized9. Since DMSO is an important solvent studies concerning solute-solvent interaction in DMSO were undertaken. In the present communication conductance studies in DMSO solutions are reported in order to test some of the interaction theories and to have a relative estimate of the solute solvent interaction for different electrolytes in DMSO. Dimethyl sulphoxide is a highly associated solvent and it is found that cations are mostly solvated in it whilst anions remain relatively unencumbered by DMSO (ref. 10). In this work solutes having cations of different sizes are used in order to understand the effect of cation or anion, if any, on the solute-solvent interaction in DMSO. The distance of closest approach between the ions and the equivalent conductance at infinite dilution is also discussed. Experimental
Analar grade salts after drying over PzOs were used without further purification. Dimethyl sulphoxide was purified by the method described in ref. 11. Measurements at 25°C of density, viscosity and specific conductance of the DMSO used were 1.096 g m1-1, 0.0198 poise and 10 -7 f~-I cm-1, respectively. All solutions were made up by weight under dry conditions. Conversion between molarity and molality was obtained from the relationship: m = 1 ~ ( d / M - M2/1000)
where M is the molarity, m is the molality, d is the density of the solution and M 2 is the molecular weight of the salt. Density was determined by the method described earlier ~2. All measurements were carried out at 25°C and 30°C. Conductance measurements were carried out with a calibrated Toshniwal conductivity bridge No. 441 at 50 Hz. The conductivity cell having cell constant 0.802_+0.001 cm -1 was used for the present study.
118
SHORT C O M M U N I C A T I O N
TABLE 1 MOLAR CONDUCTANCES FOR DMSO SOLUTIONS OF CsI AND NH4Br AT 25°C Concentration c x lO3/mol l-1
Molar conductance A obs/• 1 cm 2 tool 1
Caesium iodide 24.44 29.07 34.70 41.82 50.75 58.78 67.79 79.77
36.00 35.78 34.58 34.43 33.11 31.30 30.68 29.08
Ammonium bromide 48.25 57.33 67.25 78.65 92.37 107.40
33.16 32.07 29.74 27.47 25.98 23.83
TABLE 2 MOLAR CONDUCTANCES FOR DMSO SOLUTIONS OF NH4CI , NH4Br AND KCNS AT 30°C Concentration c x 103/mol 1-1
Molar conductance A obs./~ -1 cmz tool -1
Ammonium chloride 63.08 77.29 93.69 127.20 155.40 190.10
34.26 25.87 16.22 16.03 14.68 11.57
Ammonium bromide 40.03 47.49 57.94 69.08 84.24 103.70
35.97 33.69 31.76 28.96 27.54 25.84
Potassium sulphocyanide 17.18 22.29 39.58 53.30 75.08 98.58
46.41 41.28 40.42 39.03 36.76 34.89
119
SHORT COMMUNICATION
Results and discussion
The molar conductance values of caesium iodide and ammonium bromide in DMSO at 25°C, and of ammonium chloride, ammonium bromide, and potassium sulphocyanide in DMSO at 30°C are given in Tables 1 and 2 respectively. According to Onsager's theory the equivalent conductance for 1 :1 electrolytes will vary according to the relation:
A = Ao- [0.6936 A0+ 5.461] x/e
(I)
Therefore, a plot of A vs. x/c should be a straight line. The theoretical slope and the experimental slope are given in Table 3. TABLE 3 TEST OF ONSAGER'S EQUATION FOR CsI, NH4C1, NH4Br AND KCNS IN DMSO Salt
CsI NH4Br NH4C1 NH4Br KSCN
Temperature
Ao
/°C
/ohm
25 25 30 30 30
K 1 cm 2
Deviation ,Io~ I'~o
mol-i
45.80 52.00 53.60 57.60 50.00
( Onsager )
(Observed)
57.77 60.84 62.37 68.19 64.38
57.78 85.20 100.00 108.57 48.28
1.73 40.03 60.33 59.22 25.01
TABLE 4 TEST OF THE FUOSS, ONSAGER AND SKINNER EQUATION AND WALDEN PRODUCT FOR DIFFERENT ELECTROLYTES IN DMSO Salt
Temperature /°C
Ao/ohm a cm z mol 1
Walden product Aorl
Contact distance ( ~t )
CsI NH4Br KSCN NH~Br NH4C1
25 25 30 30 30
47.47 52.54 54.79 58.18 63.95
0.9399 1.0402 0.9697 1.0297 1.1319
2.97 2.72 3.14 2.58 2.57
Table 3 shows that in no case, except caesium iodide, is there even approximate agreement between the Onsager and the experimental slope. In general the Onsager equation holds for measurements in dilute solutions, that is, c ~<0.08424 mol 1-1. The data was further analysed by using the conductance equation of Fuoss et al. 13 for dissociated salts. The limiting conductance, along with the Walden product and the contact distances of the ions in the solution, are given in Table 4. Since in DMSO solutions, anions, especially halides, do not interact with the solvent molecules, the Ao of ammonium chloride and ammonium bromide at 30°C
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SHORT COMMUNICATION
suggests that the mobility of C1- is greater than that of Br-. With the increase in temperature dissociation of ammonium bromide increases. The greater contact distance of potassium sulphocyanide indicates interaction of sulphocyanide ion with the DMSO molecules: this may be due to the formation of a linkage between oxygen of the DMSO molecule and sulphur of the thiocyanate ion. The negative temperature coefficient of the Walden product 1~, for ammonium bromide indicates that ammonium bromide acts as a structure breaker and this is in accordance with the observation made from viscosity measurements a2. The same contact distance of the ammonium halides at 30°C is in accordance with the fact 1° that in DMSO solutions of electrolytes, only the cation is interacting with the DMSO molecule. The higher value for ammonium bromide at 25-°C suggests that the ion-solvent interaction increases with the decrease in the temperature and the ammonium ion is more solvated at 25°C than at 30°C.
Acknowledgement One of the authors (M.LIP.) is thankful to the University Grants Commission (India) for financial support. REFERENCES Y. C. Chiu and R. M. Fuoss, J. Phys. Chem., 72 (1968) 4123. K. L. Hsia and R. M. Fuoss, J. Amer. Chem. Soc., 90 (1968) 3055. R. M. Fuoss, Rev. Pure Appl. Chem. Australia, 18 (1968) 125. I. D. McKenzie and R. M. Fuoss, J. Phys. Chem., 73 (1969) 1501. L. G. Savedoff, J. Amer. Chem. Soc., 88 (1966) 664. M. B. Reynolds and C. A. Kraus, J. Amer. Chem. Soc., 70 (1948) 1709. D. P. Ames and P. G. Sears, J. Phys. Chem., 59 (1955) 16. R. L. Kay, B. J. Hales and G. P. Cunninghans, J. Phys. Chem., 71 (1967) 3925. B. Kratchvil and H. L. Yeager, Topics in Current Chemistry, Springer-Verlag, Berlin, 1972. R. T. Morrison and R. N. Boyd, Organic Chemistry, Prentice-Hall, New Delhi, 1969, p. 492. D. D. Perrin, W. L..F. Armarego and Dawn R. Perrin, Purification of Laboratory Chemicals, Pergamon Press, New York, 1966, p. 146. 12 R. L. Blokhra and M. L. Parmar, Austral. J. Chem., (1974) in press. 13 R. M. Fuoss, L. Onsager and J. F. Skinner, J. Phys. Chem., 69 (1965) 2581. 14 T. S. Sarma and J. C. Ahluwalia, Chem. Soc. Rev., 2 (1973) 203.
1 2 3 4 5 6 7 8 9 10 11
117
SHORT COMMUNICATION
Conductance of caesium iodide, ammonium chloride, ammonium bromide and potassium sulphocyanide in dimethyl sulphoxide R. L. B L O K H R A and M. L. PARMAR
Chemistry Department, Himachal Pradesh University, The Manse Building, Simla-171001 (lndia) (Received 2nd April 1974)
Introduction
Conductance has been the subject of study for the last fifteen to twenty years. During this period Fuoss and his co-workers 1~ have suggested a number of theories to explain the variation of conductance of electrolytic solutions with concentrations. Conductance data were collected for various types of salts in solvents of low to high dielectric constant s 8. Quite recently studies of conductance of DMSO solutions of salts of various types have been summarized9. Since DMSO is an important solvent studies concerning solute-solvent interaction in DMSO were undertaken. In the present communication conductance studies in DMSO solutions are reported in order to test some of the interaction theories and to have a relative estimate of the solute solvent interaction for different electrolytes in DMSO. Dimethyl sulphoxide is a highly associated solvent and it is found that cations are mostly solvated in it whilst anions remain relatively unencumbered by DMSO (ref. 10). In this work solutes having cations of different sizes are used in order to understand the effect of cation or anion, if any, on the solute-solvent interaction in DMSO. The distance of closest approach between the ions and the equivalent conductance at infinite dilution is also discussed. Experimental
Analar grade salts after drying over PzOs were used without further purification. Dimethyl sulphoxide was purified by the method described in ref. 11. Measurements at 25°C of density, viscosity and specific conductance of the DMSO used were 1.096 g m1-1, 0.0198 poise and 10 -7 f~-I cm-1, respectively. All solutions were made up by weight under dry conditions. Conversion between molarity and molality was obtained from the relationship: m = 1 ~ ( d / M - M2/1000)
where M is the molarity, m is the molality, d is the density of the solution and M 2 is the molecular weight of the salt. Density was determined by the method described earlier ~2. All measurements were carried out at 25°C and 30°C. Conductance measurements were carried out with a calibrated Toshniwal conductivity bridge No. 441 at 50 Hz. The conductivity cell having cell constant 0.802_+0.001 cm -1 was used for the present study.
118
SHORT C O M M U N I C A T I O N
TABLE 1 MOLAR CONDUCTANCES FOR DMSO SOLUTIONS OF CsI AND NH4Br AT 25°C Concentration c x lO3/mol l-1
Molar conductance A obs/• 1 cm 2 tool 1
Caesium iodide 24.44 29.07 34.70 41.82 50.75 58.78 67.79 79.77
36.00 35.78 34.58 34.43 33.11 31.30 30.68 29.08
Ammonium bromide 48.25 57.33 67.25 78.65 92.37 107.40
33.16 32.07 29.74 27.47 25.98 23.83
TABLE 2 MOLAR CONDUCTANCES FOR DMSO SOLUTIONS OF NH4CI , NH4Br AND KCNS AT 30°C Concentration c x 103/mol 1-1
Molar conductance A obs./~ -1 cmz tool -1
Ammonium chloride 63.08 77.29 93.69 127.20 155.40 190.10
34.26 25.87 16.22 16.03 14.68 11.57
Ammonium bromide 40.03 47.49 57.94 69.08 84.24 103.70
35.97 33.69 31.76 28.96 27.54 25.84
Potassium sulphocyanide 17.18 22.29 39.58 53.30 75.08 98.58
46.41 41.28 40.42 39.03 36.76 34.89
119
SHORT COMMUNICATION
Results and discussion
The molar conductance values of caesium iodide and ammonium bromide in DMSO at 25°C, and of ammonium chloride, ammonium bromide, and potassium sulphocyanide in DMSO at 30°C are given in Tables 1 and 2 respectively. According to Onsager's theory the equivalent conductance for 1 :1 electrolytes will vary according to the relation:
A = Ao- [0.6936 A0+ 5.461] x/e
(I)
Therefore, a plot of A vs. x/c should be a straight line. The theoretical slope and the experimental slope are given in Table 3. TABLE 3 TEST OF ONSAGER'S EQUATION FOR CsI, NH4C1, NH4Br AND KCNS IN DMSO Salt
CsI NH4Br NH4C1 NH4Br KSCN
Temperature
Ao
/°C
/ohm
25 25 30 30 30
K 1 cm 2
Deviation ,Io~ I'~o
mol-i
45.80 52.00 53.60 57.60 50.00
( Onsager )
(Observed)
57.77 60.84 62.37 68.19 64.38
57.78 85.20 100.00 108.57 48.28
1.73 40.03 60.33 59.22 25.01
TABLE 4 TEST OF THE FUOSS, ONSAGER AND SKINNER EQUATION AND WALDEN PRODUCT FOR DIFFERENT ELECTROLYTES IN DMSO Salt
Temperature /°C
Ao/ohm a cm z mol 1
Walden product Aorl
Contact distance ( ~t )
CsI NH4Br KSCN NH~Br NH4C1
25 25 30 30 30
47.47 52.54 54.79 58.18 63.95
0.9399 1.0402 0.9697 1.0297 1.1319
2.97 2.72 3.14 2.58 2.57
Table 3 shows that in no case, except caesium iodide, is there even approximate agreement between the Onsager and the experimental slope. In general the Onsager equation holds for measurements in dilute solutions, that is, c ~<0.08424 mol 1-1. The data was further analysed by using the conductance equation of Fuoss et al. 13 for dissociated salts. The limiting conductance, along with the Walden product and the contact distances of the ions in the solution, are given in Table 4. Since in DMSO solutions, anions, especially halides, do not interact with the solvent molecules, the Ao of ammonium chloride and ammonium bromide at 30°C
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SHORT COMMUNICATION
suggests that the mobility of C1- is greater than that of Br-. With the increase in temperature dissociation of ammonium bromide increases. The greater contact distance of potassium sulphocyanide indicates interaction of sulphocyanide ion with the DMSO molecules: this may be due to the formation of a linkage between oxygen of the DMSO molecule and sulphur of the thiocyanate ion. The negative temperature coefficient of the Walden product 1~, for ammonium bromide indicates that ammonium bromide acts as a structure breaker and this is in accordance with the observation made from viscosity measurements a2. The same contact distance of the ammonium halides at 30°C is in accordance with the fact 1° that in DMSO solutions of electrolytes, only the cation is interacting with the DMSO molecule. The higher value for ammonium bromide at 25-°C suggests that the ion-solvent interaction increases with the decrease in the temperature and the ammonium ion is more solvated at 25°C than at 30°C.
Acknowledgement One of the authors (M.LIP.) is thankful to the University Grants Commission (India) for financial support. REFERENCES Y. C. Chiu and R. M. Fuoss, J. Phys. Chem., 72 (1968) 4123. K. L. Hsia and R. M. Fuoss, J. Amer. Chem. Soc., 90 (1968) 3055. R. M. Fuoss, Rev. Pure Appl. Chem. Australia, 18 (1968) 125. I. D. McKenzie and R. M. Fuoss, J. Phys. Chem., 73 (1969) 1501. L. G. Savedoff, J. Amer. Chem. Soc., 88 (1966) 664. M. B. Reynolds and C. A. Kraus, J. Amer. Chem. Soc., 70 (1948) 1709. D. P. Ames and P. G. Sears, J. Phys. Chem., 59 (1955) 16. R. L. Kay, B. J. Hales and G. P. Cunninghans, J. Phys. Chem., 71 (1967) 3925. B. Kratchvil and H. L. Yeager, Topics in Current Chemistry, Springer-Verlag, Berlin, 1972. R. T. Morrison and R. N. Boyd, Organic Chemistry, Prentice-Hall, New Delhi, 1969, p. 492. D. D. Perrin, W. L..F. Armarego and Dawn R. Perrin, Purification of Laboratory Chemicals, Pergamon Press, New York, 1966, p. 146. 12 R. L. Blokhra and M. L. Parmar, Austral. J. Chem., (1974) in press. 13 R. M. Fuoss, L. Onsager and J. F. Skinner, J. Phys. Chem., 69 (1965) 2581. 14 T. S. Sarma and J. C. Ahluwalia, Chem. Soc. Rev., 2 (1973) 203.
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