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Name: Patrick S. Caddarao Section: 3 ChE A Group No. 2 Date Performed: Nov. 28, 2007 Experiment # 2 Refractive Index I. Introduction: Refractometer is an optical instrument that measures the extent to which light is bent when it moves from air into a sample. It is a unitless number, between 1.3000 to 1.7000 for most compunds, and is normally determined to five digit precision. [1] At the end of the experiment we are expected (a) to determine the indices of refraction of the different proporti
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   Name: Patrick S. Caddarao Date Performed: Nov. 28, 2007Section: 3 ChE A Group No. 2 Experiment # 2Refractive IndexI. Introduction: Refractometer is an optical instrument that measures the extent to which light is bentwhen it moves from air into a sample. It is a unitless number, between 1.3000 to 1.7000 for mostcompunds, and is normally determined to five digit precision. [1]At the end of the experiment we are expected (a) to determine the indices of refraction of the different proportions of liquids in a binary mixture. (b) to determine the specific andmolecular refractivities of each proportion of liquids in a binary mixture. And (c) to compare theobserved molecular refractions with calculated values. II. Methodology: Different proportions of methanol from Carl Zeiss 114648 made in West Germany andreagent grade toluene by Fisher Scientific Analytical code: T/2300/17 Batch 0418049 had been prepared for the determination of the refractive index using Abbe Refractometer by Merck KGaAmade in Darmstadt Germany. Refractive index was noted starting at 100% methanol and 0%toluene mixture. A 10% increment of toluene and 10% decrement of methanol were used in the proceeding proportions of mixtures. We ended up measuring the refractive index when we reachthe 100% pure toluene solution. The readings were taken when the demarcation line between thelight and dark intersects the cross hairs. The temperature of the binary mixture was noted everyreadings. The sample were then transferred into a pycnometer to get exactly 25 ml of the solutionand weighted through an analytical balance. The density of the solution was calculated by theformula, mass/volume and the Rs and Rm were calculated using       +−=  ρ η η  12()1( 22  s  R and       +−=  ρ η η  M  R m 2()1( 22 respectively, where M = (x 1 )(Mwt. 1 ) +(x 2 )(Mwt. 2 ).  III. Results and Discussion y = -0.2955x 2 + 0.1328x + 1.4996R 2 = 0.97531.321.341.361.381.41.421.441.461.481.51.521.5400.20.40.60.811.2Series1Poly. (Series1) Refractive indexmole fraction of methanol   Figure 1   Refractive index vs. Mole fraction of MethanolFigure 1 shows a second order polynomial series of relationship. As the mole fraction of methanol increases (mole fraction of toluene decreases), the refractive index decreases. Theequation of the line y = -0.2955x 2 + 0.1328x + 1.4996 and has a R  2 = 0.9753. The true value of refractive index of methanol at 20 ◦ C is 1.328 [3] and that of the toluene at 20 ◦ C is 1.4969 [4] . As wecompared to the true value of refractive index of the two, toluene has a greater refractive indexthan methanol that’s why refractive index decreases as mole fraction methanol increases.  y = -0.167x 2 + 0.0938x + 0.3423R 2 = 0.952400.050.10.150.20.250.30.350.400.20.40.60.811.2Series1Poly. (Series1) Specific Refractionmole fraction of methanol Figure 2 Specific Refraction vs. Mole fraction of MethanolFigure 2 shows a second order polynomial series of relationship. As the mole fraction of methanol increases, specific refraction decreases. The equation of the line is y = -0.167x 2 +0.0938x + 0.3423 and has a R  2 = 0.9524. y = -23.825x + 32.792R 2 = 0.99360510152025303500.20.40.60.811.2Series1Linear (Series1) mole fraction of methanolMolecular Refraction Figure 3 Molecular Refraction vs. Mole fraction of MethanolFigure 3 shows a linear of relationship. As the mole fraction of methanol increases,molecular refraction decreases. The equation of the line is y = -23.825x + 32.792 and has a R  2 =  0.9936. Molecular refraction was determined by using the formula       +−=  ρ η η  M  R m 2()1( 22 where M= average molecular weight = (x 1 )(Mwt. 1 ) +(x 2 )(Mwt. 2 ).MixturemethanoltolueneRiRsRmρ ◦ cXi of methanol100%0%1.344700.27498.80780.77223.51.000090%10%1.355500.27909.62820.78823.50.958980%20%1.371240.283610.58450.80023.50.912170%30%1.388340.293711.91270.80423.50.858260%40%1.4074350.303413.44920.81223.50.795550%50%1.437580.327915.98940.80024.00.721740%60%1.487950.347918.80850.82824.00.633530%70%1.4948150.348721.09800.83624.00.526320%80%1.5008350.349023.90530.84424.00.393310%90%1.5028450.346827.28900.85224.00.22370%100%1.504850.346431.91380.85624.00.0000 Table 1 Summary of Data obtained and calculated in the experimentTable 1 summarizes the data obtained in the whole experiment. It shows that a decreaseof mole fraction of methanol correspond to an increase of refractive index, density, specificrefraction and molecular refraction. Sample Calculations:A. Calculating proportions of methanol and toluene (1) 25 ml methanol + 0% toluenex = 0.000 mL toluene(2) 25 ml methanol + 10% toluenex / (25.000 + x) = 0.100x = 2.780 mL toluene(3) 25 ml methanol + 20% toluene(2.500 + x) / (25.000 + x) = 0.200x = 3.125 mL toluene
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