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Unformatted text preview: MAPUA I NST I TUTE OF TECHNOLOGY School of Chemical Engineering, Chemistry, Biological Engineering, and Material Science and Engineering Physical Chemistry Laboratory 2 - 3 rd Quarter SY 2010-2011 Neil Patrick P. Tangara , 3 rd Year B.S. Chemical Engineering Experiment No. 4 SPECTROPHOTOMETRY Meynard Austria 1 , Neil Patrick Tangara, Darlene Pudolin, Emily Rose Santos, Aeiocellis Tan, Creza Loraine Talingting 2 1 Professor; 2 Students, all from CHM171L/A31, School of Chemical Engineering, Chemistry, Biological Engineering & Material Science and Engineering, Mapua Institute of Technology ABSTRACT This experiment intends to utilize spectrophotometry to determine the visible light range based on wavelengths for the human eye and the effect of concentration on absorbance in a solution and to determine the unknown concentration of a sample using Beers plot. It was found that the human eye has a visible light range of approx. 400-650 nm. Also, concentration was found to vary directly with absorbance and inversely with transmittance. The unknown concentration was interpolated to be 0.00709 M using the best-fit-line equation generated by plotting concentration versus absorbance. This report will discuss why such a phenomenon occurs. Keywords : spectrophotometry, wavelength, absorbance, Beers plot, transmittance I N TRODUCT ION A spectrophotometer is employed to measure the amount of light that a sample absorbs. The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector. When a photon encounters an analyte molecule (the analyte is the molecule being studied), there is a chance the analyte will absorb the photon. This absorption reduces the number of photons in the beam of light, thereby reducing the intensity of the light beam. One of the most common applications of spectrophotometry is to determine the concentration of an analyte in a solution. The experimental approach exploits Beer's Law, which predicts a linear relationship between the absorbance of the solution and the concentration of the analyte (assuming all other experimental parameters do not vary)....
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