Some ionic conductivities in binary solvent mixtures: Ethylene Carbonate+ water mixtures.

 

Dr. Rajesh A. Samant*and Dr. Yogita M. Shinde

Department of Chemistry, Kishinchand Chellaram College, Dinshaw Wachha Road, Churchgate,

Mumbai – 400020 India.

*Corresponding Author E-mail: samantrajesh@yahoo.co.in

 

Ethylene Carbonate, (EC), has relatively high dipole moment and relative permittivity but its high freezing point (30⁰C) has put several restriction on the use of EC directly as solvent for electrochemical studies. EC + water mixtures are more convenient for particular utilization, as they are miscible at various proportions (Viz 20, 40, 60 and 80 mass% EC + Water) at 25⁰C with relative permittivity higher than that of water. With this background some conductance studies of monovalent salts were undertaken in these solvents. From the resulted limiting molar conductivity values the limiting ionic conductivity of some ions is reported in 20, 40, 60 and 80 weight% EC + Water at 25⁰C.

 

 

INTRODUCTION:

Ethylene Carbonate (1,3 – dioxolane – 2 - one), EC, is one of the more inert of the dipolar aprotic solvents with respect to its acid-base properties as well as other type of chemical attack. Ion – dipole type solute – solvent interactions are expectedly much favored in EC owing to its high dipole moment (4.87)¹. EC is a good solvent for electrochemical studies, as it has a high relative permittivity (89.78 at 40⁰C)² but its high freezing point (30⁰C) has put several restriction on the use of EC directly as solvent for electrochemical studies. EC + water mixtures are more convenient for particular utilization, as they are miscible at various proportions (Viz 20, 40, 60 and 80 weight % EC + Water) at 25⁰C with relative permittivity higher than that of water.

 

The conductivity measurements of monovalent salts, Potassium Chloride (KCl), Potassium Bromide (KBr), Potassium Nitrate (KNO₃), Ammonium Chloride (NH₄Cl) and Lithium Chloride (LiCl) were carried out in 20, 40, 60 and 80 mass% EC + Water. The limiting conductivity of these salts was obtained by computation of the experimental data to extrapolate of the graph of molar conductivity vs concentration.

 

The ionic conductivities of  NH₄⁺, Li⁺, Br^-, NO₃^- and Cl^-  in 20, 40, 60 and 80 mass% EC + Water are then calculated from the earlier³ reported values of ionic conductivity of K⁺, ion in these solvents.

 

MATERIAL AND METHODS:

Solvents:

Commercially available (Fluka product) EC was distilled twice under reduced pressure. In each distillation only 80% middle fraction was collected.

 

Demineralized water after double distillation was used for preparing EC + Water mass% mixtures.

 

Both EC and Water were stored in sealed containers to prevent from contamination from the atmosphere. The weighed quantities of both were mixed together to get the desired composition with accuracy of ±0.05 mass% and the transfers of required quantity was done with minimum exposure to air.

 

Chemicals:

All the salts (KCl, KBr, KNO₃, NH₄Cl and LiCl )  used for conductance measurements were of AR grade Quality (SD fine chemicals make) and were dried in vacuum oven to remove the absorbed moisture (if any) before weighing directly into the solvent to get the required experimental stock concentrations.

 

Instruments and procedure:

All weighing was done using Contech single pan digital balance with 0.1 mg sensitivity.

 

All conductance measurements were made at 25± 0.1⁰C using a dip type conductivity cell (cell constant 1.05 cm^-1) along with Toshniwal digital conductivity meter as described in the literature⁴. The conductivity meter was regularly standardized using standard KCl solutions. All conductivity measurements reported here have been calculated after correcting for solvent conductivity. All the experiments were repeated minimum twice to get concordant results.

 

The values reported here for all the measurements, in this work are within ± 0.01 unit agreements with each other.  

 

RESULTS:

The reported properties like Relative permittivity⁵, density⁵ and viscosity³ of EC + water mixtures are listed in Table 1.The results of conductivity measurements of KCl, KBr, KNO₃, NH₄Cl and LiCl in 20, 40, 60 and 80 mass% EC + water mixtures are listed in Table 2. The computation of the conductance data gave the value of specific conductance at infinite dilution, limiting conductivity (Λ₀). The values obtained by this method for limiting conductivities (Λ₀) of the five salts in 20, 40, 60 and 80 mass% EC + water mixtures are listed in Table 3. The graphical representation of the trends in Limiting conductivities are shown in   figure- 1, which shows decreasing trend as the percentage of EC increases in the mixture.

Figure 1: Limiting molar conductivity of salts in EC + Water mixtures

 

Table 1

Properties of EC + Water  mass % mixtures
Mass% EC	Relative permitivity4	Density4	Viscosity3
		gm/ cm-3	mPa.s
0	78.54	0.0997	0.89
20	80	1.0551	1.05
40	81.55	1.1178	1.18
60	83.24	1.1842	1.36
80	86.25	1.2595	1.6
100	89.78	1.321	1.85

 

 

Table 2

Conductance Data in Ec + Water mixtures at 250C
20 mass% EC + Water			40 mass% EC + Water			60 mass% EC + Water			80 mass% EC + Water
104C	Λ		104C	Λ		104C	Λ		104C	Λ
mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1
KCl
2.2	118.87		4.3	98.99		1.7	74.7		1.9	56.03
4.4	117.97		8.5	98.21		3.4	74.27		3.7	55.88
8.7	116.83		12.7	97.49		6.8	73.69		7.5	55.44
13.0	115.69		16.8	96.74		10.2	73.01		11.1	55.08
19.4	114.55		20.9	95.81		15.2	72.28		16.6	54.70
25.8	113.18		27.1	94.78		20.1	71.48		22.0	54.00
34.1	111.64		37.2	93.59		26.6	70.63		29.1	53.21
42.3	109.68		52.9	92.27		33.0	69.67		37.8	52.59
52.4	107.40		71.9	91.14		40.9	68.75		48.1	51.77
66.2	105.47		90.1	89.96		63.6	66.37		61.4	50.47
81.48	103.92					78.0	64.97		77.5	49.79
									93.0	48.91
KBr
3.0	119.89		6.0	102.51		2.0	78.28		2.7	58.15
5.9	119.13		11.9	101.93		3.9	77.93		5.3	57.71
11.9	117.99		17.8	101.46		7.9	77.09		8.0	57.26
17.7	116.69		29.6	100.64		11.8	76.26		13.3	56.74
26.5	115.68		41.3	99.78		15.6	75.41		18.6	55.99
37.9	113.95		52.9	98.88		21.3	74.51		26.3	55.4
52.0	112.15		70.1	98.15		28.9	73.38		36.6	54.91
68.5	110.48		87.1	97.11		38.1	72.39		49.2	54.27
87.3	108.2		115.0	96.00		50.8	70.83		64.0	53.44
			142.4	95.01		64.9	69.80		80.8	52.57
			169.3	94.09		81.9	67.88		99.6	51.73
KNO3
2.7	113.23		2.1	102.78		4.8	84.22		1.6	69.19
5.4	112.71		4.2	102.27		7.2	83.90		3.2	68.71
10.7	112.05		8.3	101.71		11.9	83.43		6.4	68.36
15.9	111.61		12.4	100.99		16.7	82.89		9.6	67.80
23.8	110.59		18.5	100.38		23.7	82.38		14.3	67.23
31.5	109.13		26.6	99.409		30.6	81.73		20.6	66.61
41.7	108.14		36.4	98.58		39.7	80.88		28.2	66.00
51.7	107.09		49.9	97.39		50.9	80.01		38.6	65.25
64.1	106.01		64.9	96.01		64.0	79.21		53.1	64.27
76.1	105.08		79.4	94.94		79.0	78.27		67.0	62.72
92.7	103.81		95.3	93.52		99.7	77.46		80.4	61.96
111.1	102.11		112.3	92.18		119.6	76.50		93.3	60.88
133.3	101.06		128.7	90.83
NH4Cl
1.5	127.29		2.1	101.92		2.7	85.6		2.2	61.62
3.0	126.88		4.2	101.17		5.4	85.21		4.5	61.06
5.9	126.03		6.2	100.57		8.0	84.83		7.0	60.93
8.9	125.74		10.4	99.85		13.3	84.04		11.1	60.49
13.2	124.94		14.5	98.99		18.6	83.41		15.5	59.97
18.9	124.54		20.5	98.15		25.8	82.56		22.0	59.32
26.0	123.92		28.5	96.96		36.7	81.29		32.7	58.75
35.6	121.60		38.3	95.88		49.3	79.96		43.2	57.93
48.9	120.40		49.9	94.77		64.1	78.63		57.5	57.06
61.7	119.20		62.9	93.45		78.6	77.37		73.4	56.26
74.1	118.07		77.6	92.13		97.4	76.19		92.6	55.27
86.0	116.82		95.2	91.04		112.8	75.01		111.2	54.14
108.7	115.23		112.2	90.08

 

Table 2 Contd.

20 mass% EC + Water			40 mass% EC + Water			60 mass% EC + Water			80 mass% EC + Water
104C	Λ		104C	Λ		104C	Λ		104C	Λ
mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1		mol.dm-3	S.cm.mol-1
LiCl
7.2	101.01		3.9	82.95		5.5	70.50		3.3	53.62
14.3	100.56		7.9	82.36		10.9	70.09		6.6	53.27
28.5	98.88		15.7	81.49		16.3	69.62		9.9	52.95
42.5	97.84		23.4	80.46		21.7	69.17		16.4	52.46
63.4	96.91		35.0	79.07		32.4	68.74		22.8	51.89
84.0	95.96		46.4	77.54		43.1	68.23		32.4	51.06
117.9	93.72		61.4	75.53		64.1	67.68		41.9	50.35
183.7	90.99		76.2	73.50		84.8	66.83		54.4	49.46
222.0	85.47		94.3	71.66		105.2	65.95		69.7	48.63
265.6	84.99		119.2	70.83		130.3	65.01		87.7	47.54
326.0	82.99		146.7	68.92		164.6	64.35		108.2	46.48
384.2	81.02		180.1	67.52		202.7	63.11		136.6	45.40
			212.2	65.97

 

Table 3

Limiting molar conductivities (Λ0) salts in mass% EC + water mixtures
	20 mass% EC  + Water	40 mass% EC  + Water	60 mass% EC  + Water	80 mass% EC  + Water
KCl	119.35	99.55	74.80	56.20
KBr	120.30	102.90	78.10	58.15
KNO3	113.30	102.60	84.30	69.00
NH4Cl	127.50	101.75	85.80	61.20
LiCl	101.40	83.45	70.65	53.80

 

Table 4

Limiting Ionic Conductivities (λ0±) salts in mass% EC + water mixtures
Ion		Limiting ionic conductivities  (λ0±) S.cm.mol-1
	Water **	20 mass% EC  + Water	40 mass% EC  + Water	60 mass% EC  + Water	80 mass% EC  + Water
K+ *	73.48	54.78	51.53	35.15	22.43
NH4+	73.5	62.93	53.73	46.15	27.43
Li+	38.7	36.83	35.43	31.00	20.03
Cl-	76.3	64.57	48.02	39.65	33.77
Br-	78.1	65.52	51.37	42.95	35.72
NO3-	71.5	58.52	51.07	49.15	46.57

* ref 3

** ref 5

DISCUSSION

Using the value of limiting conductivity, (Λ₀), obtained from the conductivity data and considering the limiting conductivity is an algebraic sum of ionic conductivities of all the ions present in the molecule, the value of ionic conductivities (λ₀^±) are calculated. The value of K⁺ ion reported earlier³ was used to calculate the ionic conductivity of all other ions in the solvents. The calculated Limiting Ionic Conductivities along with the reported literature value^3,4 are listed in Table 4. The graphical representation of the trends in Limiting conductivities are shown in Figure 2, which shows decreasing trend as the percentage of EC increases in the mixture.

 

Specifically in Li⁺ ion a steady marginal decrease is observed from water to 60 mass% EC + Water mixture but a sharp down fall is observed in 80 Wt % EC + Water Mixture, this indicates that 80 wt % EC + water solvates  Li⁺ ion more than any other solvent. Similar behavior is observed in case of NH₄⁺ ion also.

 

In Case of anions a sharp decrease is observed from water to 20  mass % EC + Water mixture and then it decreases marginally, which highlights the reverse behavior of the solvent in terms of salvation of anions.

 

REFERENCES:

1.       Boyd, R. H. , Extention of Stock’s Lawfor the ionic motion to include the effect of dielectric relaxation, J. Chem. Phy. 1970, 52, 1281-1283.

2.       Lee W.H., Cyclic Carbonates , In The Chemistry of Non-aqueous solvents, Logowski J.J. Ed., Academic Press, New York 1976, Vol 4, Chapter 6.

3.       Srivastava A. K., et al., Ionic conductivities in Banary solvent Mixtures .2. Ethylene carbonate + water at 25⁰C. J. Chem. Engg. Data, 1996, 41, 431.

4.       Srivastava A. K. and Desai A. R. Conductance behaviour of some potassium and tetraalkyl ammonium salts in sulfolane + Water. J. Chem Engg Data 1992, 37, 322-327.

5.       Olah G. A.; Overchuk N. A.; Remarks on the nitronium salt nitration of toluene and benzene., Can. J. Chem., 1965, 43, 3279-3293.

6.       Vogal’s Handbook of quantitative inorganic analysis.

 

 

Received on 09.03.2013       Modified on 28.03.2013

Accepted on 31.03.2013      © AJRC All right reserved