STUDY OF MOLAR REFRACTION AND POLARISABILITY CONSTANT OF AQUEOUS SOLUTIONS OF KCL AND KBRO3 AT DIFFERENT TEMPERATURES

Densities and Refractive Indices of solutions of potassium bromate (KBrO3) have been studied in water and 0.1%, 0.2%, 0.3%, 0.4% and 0.5% (w/v) aqueous solution of KCl with temperature in the range T = 298.15 ̊K313.15 ̊K. The data obtained is utilized to determine Specific Refraction (RD) and Molar Refraction (RM) of solutions. The values of Refractive indices, Molar Refraction (RM) and Molar Polarisability (α) constant are found to be decreased with decreasing concentration of solute in solvent and these results are also interpreted in terms of interaction in salt solution. It has been verified that Molar Refraction is additive and constitutive property.


INTRODUCTION
The molar refractivity is a measure of the polarisability of the molecule [1]. The study of specific refractivity, molar refractivity and polarisability of salt solutions plays a vital role not only in chemical but also in engineering, medical and biotechnical field. The best part with measurement of refractive index is that it can be measured easily with a high degree of accuracy.
Potassium bromate has been widely used in the oxidation of many organic compounds in acidic medium. This oxidation was recognized as friendly to the environment compared to the oxidation carried out by transition metal containing reagents such as chromate, permanganate, cerium and ruthenium salts. Idris S.O. et al. [2] describe the kinetics of the oxidation of L-Methionine by potassium bromate in hydrochloric acid medium. The kinetics and mechanism of the oxidation of Tartaric acid by potassium bromate in perchloric acidic medium was also studied [3]. A combination of sulfuric acid and potassium bromate in the presence of SiO2 were used as effective oxidizing agent for the oxidation of alcohol to its corresponding aldehyde and ketone derivatives in various organic solvents with good yield [4]. Potassium bromate as an oxidizing agent in a Titania-based Ru CMP slurry was studied by S. Noyel Victoria [5]. Potassium bromate and Thioglycolate are the two compounds used worldwide as hair curling solutions. The toxic effect of KBrO3 on vestibuloocular reflex system of human was studied [6]. Optical dispersion and Molar refractivities of Alkali Halide crystals and aqueous solutions were studied by A. Penzkofer, H. Glas [7] Measurement of refractive index is an essential and important work to study the thermodynamic and other physical properties such as specific refractivity, molar refractivity and polarisability of solutions which provide information about the molecular structure of the components used in the solutions. The molar refractivity reflects arrangements of the electron shells of ions in molecule and yields information about the electronic polarization of ions.
The present paper deals with the study of molar refraction and polarisability constant of KBrO3 in aqueous KCl at different temperatures.

A. Materials
The chemicals (KCl and KBrO3) were of high purity (ACS reagent ≥ 99.0%) obtained from Sigma Aldrich, used directly without further purification. Potassium bromate and potassium chloride are commercially available in the form of white crystals. Water used for solution preparation was triply distilled with specific conductance of < 10 -6 S .cm -1 . Aqueous solutions of KCl of different percentage were prepared by dissolving an appropriate amount by weight of KCl in appropriate volume of water (w/v). The different concentrations of KBrO3 in KCl were prepared by diluting the stock solution. All weighing were done on electronic Contech balance having accuracy (0.0001g).

B. Density measurements
Density measurements were performed using bi-capillary pycnometer. The pycnometer was calibrated by measuring the densities of triple distilled water. The density was measured with an uncertainty of ± 1.48 × 10 -4 g.cm -3 . The temperatures were measured with an uncertainty of ± 0.01˚K.

C. Refractive index measurements
Refractive indices of different solutions were measured with the help of Abbe's refractometer. The refractive indices values are referred to a wavelength of 589.3 nm (Na, D-line). The temperature of prism box was maintained constant at required temperature by circulating water from thermostat. The refractometer was calibrated by glass test pieces of known refractive indices supplied with the instrument. IV. RESULTS AND DISCUSSION The present investigation includes the measurement of density and refractive index of salts in water at different temperatures is given in Table No. 1 and 2. The values of densities and refractive indices of KCl and KBrO3 in water increases with increase in concentration at all temperatures under investigation. The values however decrease with increase in temperature. The increase in concentration means increase in molar mass of salt and hence density increases. The increase in refractive index with increase in concentration is due to decrease in angle of refraction or increase in angle of incidence. The decrease in density with increase in temperature is due to increase in molar volume of solvent. However the decrease in refractive index is due to the fact that the solute-solute and solute-solvent interactions weaken with increase in temperature.
Densities followed the order KBrO3>KCl for the same concentration of the salt. This is due to relative salvation, corresponding resultant volumes of system and molar mass of these salts.
The densities of both the salt solutions increased with increase in concentration in a given solution, which is because of strengthening of solute-solvent interactions. The refractive index of various solutions shows a linear relationship[13] with concentrations of potassium salts and is tabulated in Table No .The close perusal of present investigation shows that there is increase in polarizability as well as molar refraction with increase in concentration of salts. This may be due to dispersion force. It is the molecular force which arises from temporary dipole moment. The cumulative dipole-dipole interaction may create weak dispersion force resulting in increase in molar refraction and polarizability.