1. on concentration [2]. U.V. Biradar and S.M.

1.     
Introduction:

Refractive
index is one of the most important optical properties of a medium. It is a fundamental
property of a solution which can vary with temperature, composition,
concentration and incident light wavelength. It plays vital role in many areas
of material science especially in thin film technology and fibre optics and in
many branches of science like physics, biology and chemistry and engineering.
Knowledge of the refractive index of aqueous solutions of salts and biological
agents is of crucial importance in applications of evanescent wave techniques
in biochemistry. It is mostly applied to identify a particular substance,
confirm its purity, or measure its concentration. Mostly it is used to measure
the concentration of a solute in an aqueous solution. In case of
sugar solution, the refractive index can be used to determine the sugar content
(Brix degree). It can also be used in determination of drug concentration in
pharmaceutical industry. It is used to determine the focusing power of lenses
and the dispersive power of prisms. It is used for estimation of thermo
physical properties of hydrocarbons and petroleum mixtures. Poonam Pendke and
K. Das have used Abbe refractometer for measuring refractive indices of the
polymer. They studied the variation of refractive indices with wavelength for
pure and doped PMMA samples at various temperatures. For all the temperatures
the refractive indices was found to be decreasing with increasing wavelengths
and by increasing doping % its refractive indices was also found to be increases
1. Subedi D.P., Adhikari D.R.,
Joshi U.M., Poudel H. N. and Niraula B. have used specially constructed hollow
prism to measure the refractive index of liquids with the help of an optical
spectrometer. They studied the variation of refractive index of water as a
function of temperature and showed a linear dependence of refractive index of
water on temperature in the range 30°C- 70°C. They also studied the variation
of refractive index of common salt, sugar, propanol-1, sucrose and potassium
chloride solution with concentration and found the linear dependence of
refractive index on concentration 2. U.V.
Biradar and S.M. Dongarge have studied the variation of refractive index of NaCl
salt solution with concentration and found the linear dependence of refractive index
on concentration 3. Zhu Xingyu, Mai
Tiancheng and Zhao Zilong have presented the variation of refractive index of multi
component system (CuSO4-NaCl-H2O) related to each
solute’s molar concentration and found a linear relationship 4. Manu Joseph and Ignatius J. have shown that
the refractive index has a linear dependence on the concentration in addition
to temperature in the case of Zinc acetate and Lead acetate solution 5. Jassim Mohamed Jassim and Noor Salah
Khudhair have explained the effect of temperature and concentration on the
refractive index of water using the Michelson interferometer 6. Chang-Bong Kim1 and Chin B Su measured
the refractive index of water and several liquids at wavelengths of 1310 and
1551 nm using the ?bre optic Fresnel ratio meter 7. A. Joshi, N. D. Haynes, D. E. Zelmon, O. Stafsudd and R. Shori
have conducted measurements of the refractive index as a function of wavelength
and its dependence on temperature and concentration  of  Er3+doped
ceramic Y2O3 8. Ruy
Batista Santiago Neto, Jos´e Paulo Rodrigues Furtado de Mendonc¸a and Bernhard
Lesche have determined the absolute values of refractive index of of
transparent liquids using an Interferometric Method 9. U.V. Biradar, S.M.
Dongarge and N. V. Wani have studied the variation of refractive index of KCl
salt solution with concentration and found the linear dependence of refractive
index on concentration 10.

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2.     
Material and Method:

Abbe
Refractometer Model RSR-1 is available in our laboratory which is widely used
in industries in diversified fields, for research and development and in
teaching establishment. It provides a fast and convenient method of measuring
refractive index and mean dispersion of transparent liquids, solutions and
solids. The instrument is capable of determining the percentage of sugar
contents in saccharose solutions. It delivers consistent repeatable results
free from user subjectivity. Accuracy of the refractive index is 0.001 by
direct reading and 0.0001 by estimation.

A
ray of monochromatic light passing from one medium into another is refracted or
bent towards or away from the normal depending upon the optical nature of two
media. According to Snell’s law- R.I. (n) = sin i / sin r. Refractive index
depends upon temperature, the chemical nature of substance and wavelength of
the light. If the second medium is solution, refractive index also depends upon
the concentration of the solution. So it can be used to identify a pure substance
and to determine the composition of homogeneous transparent binary mixture.

Experimental
procedure for measuring refractive index is followed as per given in the manual
provided with the instrument. To study the variation of refractive index of
KCl, KBr and KI solution as a function of concentration, an electronic balance
is used to the weigh the salts and solutions of 2M concentrations are prepared
by dissolving the salts in 50 ml of distilled water. Solutions of lower
concentrations (1M, 0.5M, 0.25M and 0.125M) are prepared by diluting with
water.

 

3.     
Result and Discussion:

Refractive
index of salt solutions KCl, KBr and KI as a function of concentration is
depicted in Table 1, 2 and 3 respectively. In case of all three salt solutions,
it is found that the refractive index is decreased when the concentration is
reduced. For 2M solution, refractive index is as high as 1.3540 (KCl), 1.3600 (KBr)
and 1.3623 (KI) which reduces to 1.3386 (KCl), 1.3403 (KBr) and 1.3453 (KI) when
the solution is diluted to a concentration of 0.125M. It is because with the
decrease in concentration, the density of the solution also decreases resulting
a decrease in refractive index. This linear dependence of refractive index with
concentration is also presented in the form of graph.

Refractive Index of
Water = 1.3310

 

 

 

 

 

 

 
Conc.
 

Table 1: Refractive Index of KCl Solution

I

II

III

Mean

2.0
M

1.355

1.353

1.354

1.3540

1.0 M

1.350

1.351

1.350

1.3503

0.5 M

1.345

1.344

1.344

1.3443

0.25M

1.341

1.341

1.342

1.3413

0.125 M

1.338

1.339

1.339

1.3386

 

 

 
Conc.
 

Table 2: Refractive Index of KBr Solution

I

II

III

Mean

2.0
M

1.359

1.360

1.361

1.3600

1.0 M

1.353

1.353

1.352

1.3526

0.5 M

1.348

1.349

1.349

1.3486

0.25M

1.344

1.344

1.345

1.3443

0.125 M

1.340

1.341

1.340

1.3403

 

 

 
Conc.
 

Table 3: Refractive Index of KI Solution

I

II

III

Mean

2.0
M

1.363

1.362

1.362

1.3623

1.0 M

1.358

1.359

1.358

1.3583

0.5 M

1.351

1.353

1.352

1.3520

0.25M

1.346

1.347

1.347

1.3466

0.125 M

1.345

1.345

1.346

1.3453

 

 

 

 

 

 

4.     
Conclusion:

Experimental results
showed that Abbe Refractometer technique could be safely employed to study the
dependence of refractive index of solutions on their concentration. A linear
dependence of refractive index of salt solutions on their concentration was
observed.

 

5.     
References:

1 Poonam Pendke, K. Das, “Variation of Refractive
Index of PMMA with temperature and different doping % of TiO2”, Int.
J. of scientific research and management, Vol. 3, Issue10, Pages 3626-31, 2015.

2 Subedi D.P., Adhikari D.R., Joshi U.M., Poudel
H. N., Niraula B., “Study of temperature and concentration dependence of
refractive index of liquids using a novel technique”, Kathmandu university
journal of science, engineering and technology, Vol. II, No.1, Feb 2006.

3 U.V. Biradar, S.M. Dongarge, “Refractive Index of
Salt (NaCl) from Aquous Solution”, Int. J. of Computer & Mathematical
Sciences, Vol. 4, Issue 12, Dec 2015.

4 Zhu Xingyu, Mai Tiancheng and Zhao Zilong, “Relationship
between Refractive Index and Molar Concentration of Multi-Component Solutions”,
Advances in Computer Science Research, Vol. 71, 4th Int. Conf. on Machinery,
Materials and Information Technology Applications, 2016.

5 Manu Joseph and Ignatius J., “Comparison of alteration
of refractive index of liquid with temperature and concentration”, Int. J. of
Pure and Applied Physics, Vol. 13, No. 1, Pages 167-171, 2017.

6 Jassim Mohamed Jassim and Noor Salah Khudhair, “Study
the Effective a Temperature and Concentration on Refractive Index of Water by
Using Michelson Interferometer”, Int. J. of Scientific Engineering and Research,
Vol. 3, Issue 11, Pages 27-30, Nov 2015.

7 Chang-Bong Kim1 and Chin B Su, “Measurement of
the refractive index of liquids at 1.3 and 1.5 micron using a ?bre optic
Fresnel ratio meter”, Institute Of Physics Publishing, Measurement Science And
Technology, Pages 1683–86, 2004.

8 A. Joshi, N. D. Haynes, D. E. Zelmon, O.
Stafsudd and R. Shori, “Impurity concentration and temperature dependence of the
refractive indices of Er3+doped ceramic Y2O3”,
Optical Society of America, Vol. 20,  No.
4, Optics Express, 4428-35, Feb 2012.

9 Ruy Batista Santiago Neto, Jos´e Paulo Rodrigues
Furtado de Mendonc¸a and Bernhard Lesche, “Determination of Absolute Values of
Refractive Index of Liquids Using an Interferometric Method”, Revista de
F´?sica Aplicada e Instrumentac¸ ˜ao, Vol. 17, No. 2, Junho, 2004.

10 U.V. Biradar, S.M. Dongarge and N. V. Wani, “Refractive
Index of Salt (KCl) from Aquous Solution”, Int. J. of Computer &
Mathematical Sciences, Vol. 6, Issue 2, Feb 2017.