Journal of Physical Chemistry & Biophysics
Open Access
ISSN: 2161-0398
+44 1478 350008
ISSN: 2161-0398
+44 1478 350008
Research Article - (2012) Volume 2, Issue 3
Conductivity method is used for the study of the dissolution of Ca(OH)2 in water and in mixed solvent systems. The thermodynamic parameters for the dissolution of Ca(OH)2 such as ΔG°, ΔS°, ΔH° were calculated from solubility values at different temperatures in aqueous medium and in mixed solvent systems (Water+1-propanol, water+2-propanol,water+DMSO and water + THF). It was found that the solubility and solubility product of Ca(OH)2 significantly decreased linearly by increasing percentage composition of the mixed solvent systems. The Gibbs free energy ΔG°, enthalpy ΔH° and ΔS° were also changed. These results were in agreement with the dielectric constant value of the solvents used in the study.
<Keywords: Thermodynamic parameters; Mixed solvent system; Solubility product; Conductivity
Calcium Hydroxide has great application in the field of metallurgy, agriculture, paper and glass industry. It is also used in soil amendment to supply calcium to crops [1,2]. It is widely used in manufacturing of steel, chemicals, cement and glass. It is also be used to control air pollution, water and sewage wastewater treatment, diluents and carriers of pesticides such as lime-sulfur, Bordeaux mixture, bleach production, and other chemical substance [2,3]. It is also used in paper industry to dissolve lignin as for the coagulation [2,3].
In the present research work, conductometric titration was used for the study of the influence of mixed solvent system on the solubility of Ca(OH)2.
The study of equilibrium for many chemical reactions has taken into consideration for the determination of thermodynamic investigation.
The molar solubility “S” solubility product and Gibbs free energy is determined from following equation [1],
Ksp = [Ca+2] [2OH-]2 = 4S3 (1)
ΔG = -R T l n (Ksp) (2)
Where “R” is a universal gas constant, T is the absolute temperature and ΔG° is the Gibbs free energy ΔG° is related to ΔH° and ΔS° by the following equation [1].
ΔG°= H°- TΔS° (3)
The value of ΔG° calculated at two different temperatures T1 and T2 provide the values of ΔH° and S° over a small temperature range.
In previously reported only the study of simple conductomertic titration of Ca(OH)2 in aqueous medium at 25 and 100°C. In present work reported the effect of solvent on the dissolution Ca(OH)2.
In the present research work, conductivity method was used for the study of the influence of mixed solvent system on the solubility of Ca(OH)2.
All reagents are used such as Ca(OH)2, (E. Merck), 1-Propanol (E. Merck), 2-propanol (E. Merck), Tetrahydrofuran (E. Merck), Dimethyl sulfoxide (E. Merck), Hydrochloric acid (E. Merck), Oxalic acid (E. Merck), Sodium hydroxide (E. Merck) and Phenolphalein (E. Merck) each of these analytical grade reagent. These stock solutions were prepared in double distilled water.
Conductivity meter HANNA (HI- 8633) (Romania), IKACombimag RCH magnetic stirrer (Germany) Thermostat (Chiller) Haake, (Type T 52, V 220, No 76400, Germany) Electrical Balance (Mettler college 150, Germany) (Table 1).
| S # | % of 1-propanol | Parameters in mixed solvent system | |||
|---|---|---|---|---|---|
| Ksp x106 (M3) | ∆ G (Kj/mole) | ∆ H (Kj/mole) | ∆S (J/mole) | ||
| 1 | 0 | 9.19±0.3 | 26.79±0.06 | -20.8±0.21 | -171±0.43 |
| 2 | 10 | 3.88±0.30 | 28.79±0.227 | -12.91±0.03 | -150±2.13 |
| 3 | 20 | 1.53±0.02 | 30.94±0.077 | -5.75±0.06 | -132±0.76 |
| 4 | 30 | 0.55±0.06 | 33.31±0.478 | -5.32±0.21 | -139.6±1.21 |
| 5 | 40 | 0.064±0.01 | 39.66±0.52 | -47.31±0.23 | -302±1.42 |
| 6 | 50 | 0.00864±0.00069 | 48.23±0.11 | -74.83±0.31 | -489.6±0.78 |
Table 1: Effect of mixed solvent system (water+1-propanol) on the Ksp and thermodynamic parameters Ca(OH)2 at 5±1°C.
Preparation of stock solution of Ca(OH)2
The conductometeric titration was performed in order to determine the solubility of Ca(OH)2, at 5, and 30 ± 1°C. The following procedure of was followed.
Stock solution of Ca(OH)2 was prepared by dissolving 0.1 g in 100 ml volumetric flask having different percentage composition (i.e. 5%, 10% , 20%, 30%, 40%, and 50%) of a mixed solvent system (1-propanol, 2- propanol, THF and DMSO). For this purpose solution was stirred for 30 minutes and then this solution was kept overnight to get maximum saturation (Table 2).
| S # | % of 2-propanol | Parameters in mixed solvent system | |||
|---|---|---|---|---|---|
| Ksp x106 (M3) | ∆ G (Kj/mole) | ∆H (Kj/mole) | ∆ S (J/mole) | ||
| 1 | 0 | 9.19±0.3 | 26.79±0.06 | -20.8±0.21 | -171±0.43 |
| 2 | 10 | 3.54±0.12 | 25.00±0.0719 | -23.59±0.12 | -189.2±2.11 |
| 3 | 20 | 0.55±0.059 | 33.29±0.239 | -10.05±1.21 | -156.8±0.02 |
| 4 | 30 | 0.146±0.0031 | 36.37±0.387 | -12.54±2.32 | -176.4±2.1 |
| 5 | 40 | 0.0233 ±0.001 | 42.08±0.350 | -28.19±0.21 | -244±2.31 |
| 6 | 50 | 0.000953±0.00017 | 48.00±0.22 | -36.84±21 | -305.2±1.1 |
Table 2: Effect of mixed solvent system (water+2-propanol) on the Ksp and thermodynamic parameters Ca(OH)2 at 5±1°C.
The next day the saturated solution of Ca(OH)2 was filtered using Whatman filter paper 60°A. A 25 ml of filtered solution of Ca(OH)2 was titrated with standard solution of HCl (0.03 ± 0.001 M) and the conductivity was recorded using conductivity meter. The reacting mixture flask was placed in water bath during the whole titration and temperature was controlled by thermostat at a fixed temperature.
In mixed solvent systems (1-propanol, 2-propanol, DMSO & THF + water) the conductance of Ca(OH)2 was little by little decreased by the addition of each volume (ml) of Standard HCl (0.03 ± 1 N) by the mutual exchange of H+ and OH ions from acid with analyte after the equivalence point, conductance of mixture is raised sharply in increasing the H+ ion in solution. This is shown in Figure 1.
Figure 1: Titration curves of the f Ca(OH)2 in mixed solvent system (water+ 1- propanol) at 5 ± 1°C.
The equivalence point of the Ca(OH)2 was also shifted with change of the composition of solvent systems which is shown in Figure 2. In general decreasing phenomenon was observed in each composition of (0%, 10%, 20%, 30%, 40% and 50%) of (1- propanol +water) solvent system at 5 and 30 ± 1°C. Similar trend was also observed in 2-propanol, DMSO and THF. However the dissolution of Ca(OH)2 was decreased slightly and by increasing temperatures. The reversed trend in dissolution against temperature, in Ca(OH)2 was found due to its lattice energy. The solvation of ion was possibly influenced by temperature in two ways. For instance it has been reported that ionsions interaction is usually decreased by increasing temperature that results in the solvation of ions which enhances by rise in temperature [4-7]. However, the solvation of ions may inversely be influenced by the rise in temperature, were a possible decrease in solvation occurs with the rise in temperature.
Figure 2: Effect of mixed solvent systems on equivalence point of Ca(OH)2 at 30±1°C.
The solubility of the various soluble salts in solutions in aqueous medium were calculated at 25°C, but this paper the solubility of Ca(OH)2 were studied in mixed solvent systems notice able thing is that the solubility of Ca(OH)2 V/S different % composition of mixed solvent systems is showed linear pattern at 5 and 30 ± 1°C which is shown in Figure 3. These decreasing patterns of the solubility of Ca(OH)2 in mixed solvent systems due to decreasing the dielectric constant value of the solvent (Table 3).
| S # | % of DMSO | Pameters in mixed solvent system | |||
|---|---|---|---|---|---|
| Ksp x106 (M3) | ∆G (Kj/mole) | ∆ H (Kj/mole) | ∆S (J/mole) | ||
| 1 | 0 | 9.19±0.3 | 26.79±0.06 | -20.8±0.21 | -171±1.8 |
| 2 | 10 | 3.47±0.20 | 39.92±0.21 | -22.37±0.12 | -185.2±4.3 |
| 3 | 20 | 0.944±0.18 | 40.57±0.321 | -20.19±1.21 | -188±0.21 |
| 4 | 30 | 0.108±0.039 | 41.21±0.56 | -71.37±0.32 | -159±0.65 |
| 5 | 40 | 0.0396±0.0006 | 40.80±0.45 | -26.38±0.01 | -233±3.21 |
| 6 | 50 | 0.000702±0.00022 | 52.17±0.621 | -15.76±0.21 | -232±3.21 |
Table 3: Effect of mixed solvent system (water+ DMSO) on the Ksp and thermodynamic parameters Ca(OH)2 at 5±1°C.
Figure 3: Effect of mixed solvent system on the solubility of Ca(OH)2 at 5±1°C.
The Ksp values of Ca(OH)2 were decreased with the increase in percentage composition of mixed solvent systems up to 30%. Beyond this composition they remained unchanged in all mixed solvent systems at all temperatures; however, this trend was comparatively similar to that of solubility which is shown in Figure 4.
Figure 4: Effect of mixed solvent system on the solubility product of Ca(OH)2
at 5±1°C.
The plot of Δ°G of Ca(OH)2 V/S solvent composition were found to be linear at all temperatures. This linear increasing trend with increasing percentage composition in all these mixed solvent systems is almost similar up to 30% solvent composition, although having a lessers gradient. Above 30% to 50% this response was prominent in Ca(OH)2. The maximum change in Δ°G was determined in Ca(OH)2. This can be explained on the bases of change in structure change, dielectric constant values, ion solvation, crystal forces and ionic radius of the Ca(OH)2 positive value of the Δ°G explain that the solubility of the Ca(OH)2 is very low [7]. In other words these Ca(OH)2 when dissolved in these mixed solvent systems followed non-spontaneous dissolution process in forward direction hence, producing positive values of Δ°G [7-10].
However the Ca(OH)2 are unfortunately less soluble and has low dissolution in water and mixed solvent system., the dissolution enthalpies of the Ca(OH)2 could not measured directly but have only been evaluate by using formula which explain earlier [11-16] (Table 4).
| S # | % of THF | Pameters in mixed solvent system | |||
|---|---|---|---|---|---|
| Ksp x106 (M3) | ∆G (Kj/mole) | ∆ H (Kj/mole) | ∆S (J/mole) | ||
| 1 | 0 | 9.19±0.3 | 26.79±0.06 | -20.8±0.21 | -171±1.8 |
| 2 | 10 | 3.47±0.20 | 29.05±0.077 | -14.28±0.03 | -185.2±4.3 |
| 3 | 20 | 0.944±0.18 | 32.06±0.308 | -24.72±0.06 | -188±0.21 |
| 4 | 30 | 0.108±0.039 | 37.05±0.66 | -6.02±0.21 | -159±0.65 |
| 5 | 40 | 0.028±0.0013 | 41.64±0.210 | -38.41±0.01 | -278±0.599 |
| 6 | 50 | 0.000702±0.00022 | 48.71±1.45 | -9..205±0.31 | -232±3.21 |
Table 4: Effect of mixed solvent system (water + THF) on the thermodynamic parameters Ca(OH)2 at 5±1°C.
The enthalpy and entropy values of Ca(OH)2, in mixed solvent systems showed almost similar and linear trend. The entropy values of the systems having some scattering having positive and negative values, within percentage composition of mixed solvent system (0–50%). In general it can be concluded that the values of enthalpy followed almost similar behavior with respect to enthalpy changes in these mixed solvent systems and showed both positive as well as negative behavior similar to the trend reported in the literature [8]. The reason of such trend as explained in the reported work is the possibility of destabilization of Ca(OH)2 in some solvent media decreasing enthalpy range, within a narrow range, which was also appeared in the present research work. Positive and negative enthalpy values confirmed that the destabilization of Ca(OH)2 in these mixed solvent systems similar to reported work [9]. However, the enthalpies and entropies of Ca(OH)2 obtained in this way to small changes of the solubility data so that the values calculated from the reported solubility data scatter considerably.
Effect of time on Conductivity at room temperature in mixed solvent systems
Conductivity of Ca(OH)2 both in the presence and absence of mixed solvent systems was gradually decreased with increasing the percentage composition which is shown in Figures 5-7. The reason of this behavior may be correlated with the possible association of the Ca(OH)2 resulting decrease in the OH- conc. confirmed of low conductance values. The other mixed solvent systems were not tried due to instability of the test electrode probe, which was found to be effected in THF and DMSO solvent system, therefore these solvent system were not include this comparative study [17-21].
Figure 5: Effect of mixed solvent systems on Gibbs Free Energy of Ca(OH)2 at 30±1°C.
Figure 6: Effect of time on conductivity of freshly prepared saturated solution of Ca(OH)2 in 1-propanolat 30±1°C.
Figure 7: Effect of time on conductivity of freshly prepared saturated solution of Ca(OH)2 in 2-propanol at 30±1°C.