Light Absorbance (Lab Report #4).docx - Nick Procaccio AP...

This preview shows page 1 - 3 out of 8 pages.

Nick Procaccio AP Chemistry Period 6-7 Analysis of Food Dyes in Beverages Goal: To analyze the food dye content in beverages (in our case, Gatorade) using spectrophotometry as the technique so we can learn how light reacts with matter. Background Info: The color of a solution can be used to gain information about the composition of the solution. Spectroscopy, the study of interaction of light and matter, can provide this information. In this lab we used a spectrophotometer . A spectrophotometer is an instrument that uses electromagnetic radiation of a specific wavelength to analyze the absorption or transmission of radiation by a sample. In this investigation, we used a visible spectrophotometer which scans the visible region of the electromagnetic spectrum (380nm – 750nm). To find the concentrations of our solutions, we used spectrophotometry , which is an analytical procedure that uses electromagnetic radiation to measure the concentration or molarity of a substance. The absorption of visible light by a substance results from electron transitions (a ground state electron becomes excited and moves to a higher energy level. The specific difference between two electron energy levels determines the specific wavelength of light absorbed by a substance. By measuring the visible light spectrum of a substance, we can determine the optimum wavelength for spectrophotometric analysis. In our case, since we are using FD&C Blue 1 dye, the optimum wavelength will be 630nm because it is the maximum absorbance of the substance. The wavelength of light absorbed by a substance is a characteristic of its molar or electronic structure. The more concentrated it is, the more light will be absorbed and vice versa. By using the percent transmittance equation (Absorbance = -log Percent Transmittance || A=-log %T), and Beer’s Law [A= e bc where A=amount absorbed, e =molar absorptivity coefficient (which is 130,000 M -1 cm -1 for the blue dye and 25,900 M -1 cm -1 for the red dye), b=the length of the sample cell, and c=concentration.], we were able to gain information of the composition of our solutions. Intro Activity: BLUE Step 1: We first turned on the spectrophotometer and allow it to warm up for 15 minutes. (not the new ones) Step 2: For the blue solution, we selected the 630nm wavelength because the optimum wavelength for spectrophotometric analysis of a dye solution is generally determined from the wavelength of maximum absorbance. The max absorbance for FD&C Blue 1 (dye) is 630nm. In laymen’s terms, the 630nm wavelength has the highest absorbance; meaning that most of the colors are absorbed and the blue light is transmitted. Step 3: We then obtained 50ml of our stock solution which contained of water and blue dye.
Step 4: Next, we made 6, 10ml solutions by combining the different volumes of the stock solution with different volumes of water. (We also had one 100% stock solution and one 100% water solution for zeroing) To make the 2ml water – 8ml stock solution, we filled a 10ml graduated cylinder with 8ml of stock solution and then filled it to the 10ml mark with water.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture