VOLUME 18, NO2, JUN 1996

Partition coefficient of amphiphilic hemicyanine dyes between water and micelles of sodium dodecyl benzene sulfonate

The solubilization of amphiphilic hemicyanine dyes i.e., [1] (Dimethylamino) stilbazolium butyl sulfonate, [2] (Dihexylamino) stilbazolium butyl sulfonate, into micelles of an anionic surfac ant, sodium dodecyl benzene sulfonate (SDBS), was studied as a function of SDBS concentration above the critical micelle concentration. The micelle-water partition coefficient, K-x, and the standard free energy change of solubilization, Delta G(p) degrees, of the dyes in SDBS micelles were determined at 25.0 degrees C by a differential spectroscopic method. The solubilization of more hydrophobic dye in micelles was greater than the less hydrophobic dye.read more

---

M A KHAN ,S S SHAH ,

Characterization of Ludwa soil

The characterization of a soil sample collected from Ludwa near Khewra has been carried wt using X-ray spectrometric techniques and nitrogen adsorption. X-ray diffraction investigations show the presence of quartz and muscovite minerals. ?he X-ray fluorescence study reveal that major constituents of the soil are SiO2 and Al2O3 while the oxides of calcium, copper, iron, cobalt and manganese are minor constituents. ?he pore size distribution curve obtained through nitrogen adsorption indicates the mesoporous nature of the clay with a surface area of 20.80 m(2)/g and having a pore volume of 0.493 cm(3)/g.read more

---

R QADEER ,M S CHAUDHARY ,M SALEEM ,R HUSSAIN ,

Analysis of the coal by pyrolysis gas chromatography effects of internal mineral matters on the yields of lower hydrocarbons

Pyrolysis of eight representative mat samples both in their raw and demineralized forms were carried out at 680 degrees C Production of C-1-C-5 hydrocarbons were monitored by gas chromatography. A comparison of the total yields of lower hydrocarbons from raw and demineralized coals was made, The results indicate an increase in the yields of lower hydrocarbons from demineralized coals as compared to their raw forms.read more

---

I ULLAH ,I A AWAN ,

Effect of solvent quality on the viscosity of dilute solutions of PVC

The dilute solution properties of two Poly(vinyl chloride) i.e., PVC samples of molecular weight 200,000 and 100,000 were studied viscometrically in four solvents. The effect of the nature of the solvent was determined showing the solvent power for PVC to be cyclohexanone > tetrahydrofuran > cyclopentanone > dioxane on the basis of [eta] and K-H. Hydrodynamic volume values are also reported for these PVC-solvent system and a similar order of solvent power is suggested. Unperturbed chain dimensions for PVC were determined by using Deb and Chatterjee equation for non-theta solvents and the values are discussed.read more

---

M S KHAN ,N M KHAN ,A SAEED ,

Diffusion of ethyl methyl ketone, methyl alcohol and acetyldehyde vapours in chromatographic alumina gel

Organic vapours such as ethyl methyl ketone, methyl-alcohol and acetaldehyde were adsorbed on the alumina gel between 273 K-298K under vacuum of 10(-4) to 10(-5) mm Hg, achieved by rotary and oil diffusion pimps. Cahn 1000 electro-microbalance and X-Y Beckman chart recorder were used for recording the data Kinetic parameters such as rate constant, Knudsen diffusivities, bulk diffusivities and effective diffusivities were evaluated through Fick type equation. The effect of temperature on the sorption of these organic vapours has also been discussed.read more

---

M KHAN ,M AFZAL ,

Removal of Co(II) ions from water by sorption on China clay

The adsorption of Co(lI) by well characterized China clay in the pH range (3.0 - 6.5) at various temperatures followed the Langmuir isotherms. Co(IT) removal is favoured by low concentration. low temperature, and low pH. The high adsorption capacity at low pH is attributed to the content of silica in China clay.read more

---

M A QAISAR ,S BEGUM ,F U KHAN ,

Dissociation constant studies of citric acid at different temperatures and in different organic-water solvent systems

Thermodynamic dissociation constants of citric acid is being studied at different temperatures from 25 to 50 degrees C at 5 degrees C interval and in 10, 20, 30 and 40 percent v/v dioxane-water, methanol-water, ethanol-water and acetonitrile-water solvent systems. The resolution of acid strength in dioxane, methanol, ethanol and acetonitrile relative to that in water has been determined Thermodynamic parameters that are Gibb's free energy (Delta G), enthalpy (Delta H) and entropy (Delta S) at different temperature have also been studied. Changes in pKn values on account of dielectric constant and hydrogen bonding have been discussed. Result shows greater resolution in mixed organic solvents than in water.read more

---

S UDDIN ,A W K KHANZADA ,A T MUFTI ,

Determination of ionization constants of substituted phenols by potentiometry and liquid chromatography

Ionization constants of phenol, p-cresol and orthochlorophenol have been determined at varying temperature from 25 to 50 degrees C and in 10, 20, 30 and 40 percent methanol-water solvent system at 25 degrees C by potentiometry. pK(a) values of all these compounds also been determined in varying percentage of methanol-water solvent system by liquid chromatography on a reversed phase column at 25 degrees C The purpose of this investigation was to obtain the data for the dissociation of phenol derivative using diverse methods with particular emphasis on the effect of chloro (-C1) and methyl (-CH3) group on phenyl ring which in turn effect on pK(a) values. Results obtained by both methods were compared and effect of substituents on phenyl ring is being discussed in light of Hammets equations. Potentiometric data was analysed by computer program written in GW-BASIC for calculation of pK values.read more

---

S UDDIN ,M I BHANGER ,A W K KHANZADA ,

Determination of ionization constants of overlapping dibasic acids in acetonitrile-H2O mixtures

Dissociation constants of few overlapping dibasic acids in acetonitrile at 25 degrees C have been studied by potentiometric method Data were analyzed by computer program written in GW-BASIC for calculation of pK(a) values of overlapping dibasic acids. Because of ion pair formation the incomplete dissociation of the compound has been taken into account in the calculation of pK(a) values. The resolution of acid strength in acetonitrile relative to that in water has been determined for each compound by plotting the pK(a) values vs. percent composition of solvent. Gibb's free energy (Delta G(theta)) is also studied. The results show greater resolution in acetonitrile than in water.read more

---

S UDDIN ,A T MUFTI ,A W K KHANZADA ,

Measurement of the apparent dissociation constants of hydrofluoric acid in concentrated electrolyte environments and their relationship to the thermodynamic value

The notable presence of fluoride in African rift valley salt lakes has important hydrochemical and mineralogical implications. We have studied the fluoride equilibria to determine apparent Ka values for HF by the method of Vanderborgh over an extended range of ionic strengths covering the lake-like electrolyte environments of interest in a target lake, The apparent pKa values of 2.990, 2.929, 2.820 and 2.739 were obtained for ionic strengths of 0.266, 0.584, 1.024 a;ld 1.419 respectively. When extrapolated to infinite dilution (zero ionic strength), these yield the thermodynamic Ka value of 7.07x10(-4) which is in good agreement with other literature values.read more

---

G MHINZI ,D MOSHA ,Q QULWI ,