# Determination of Dye Concentration by

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DETERMINATION OF DYE CONCENTRATION BY SPECTROPHOTOMETRY Abstract The purpose of this lab is to determine the molar concentration of a food dye in an unknown solution. To determine the concentration of a food dye, UV light with different wavelength is passed through erythrosin B using spectrophotometer to find the wavelength that yields the highest absorbance. The wavelength with highest absorbance is passed through different concentration of erythrosin B solution and recorded the absorbance. The concentration of the solution is calculated by using Beer’s Law. First using the various dilutions of the solution and their absorbance, graph is plotted to determine the slope. With the slope and absorbance from the data table, molarity can be calculated using formula, absorbance equals slope times molarity. Procedure Refer to: Laboratory Manual for Chemistry 1A. Chabot College, Hayward, CA, 2012. Page 105 and 106. Safety Wear safety glasses. Wash hands properly upon contact with food dye. Dispose waste in proper place. Do not operate spectrophotometer without instruction. Data See attached data sheet. Concentration erythrosin, M Absorbance at λ max 1.00*10^-5 0.802 8.00*10^-6 0.640 6.00*10^-6 0.550 4.00*10^-6 0.374 2.00*10^-6 0.206 1.00*10^-6 0.131 Absorbance curve of erythrosin B: Beer’s Law: λ, nm Absorbance 480 0.426 490 0.430 500 0.438 510 0.518 520 0.725 526 0.820 530 0.765 540 0.385 Calculation M1 * V1 = M2 * V2 where, M1 = molarity of erythrosin B stock solution V1 = volume of erythrosin B stock solution M2 = molarity of diluted erythrosin B V2 = volume of diluted erythrosin B 10 mL: M2 = (1.00*〖10〗^(-4) M*10.00 mL)/100.00mL = 1.00*〖10〗^(-5) M 8 mL: M2 = (1.00*〖10〗^(-4) M*10.00 mL)/100.00mL =