Experiment # 9: Optical Method of Analysis Use of Beer’s Law on a KMn04 Gregorio, Justin Edrik A.
Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
The purpose of this analytical laboratory experiment is to determine the unknown concentration of potassium permanganate (KMnO4) solution by finding its absorbance through the use of spectrophotometer. The preparation of four known concentration of KMnO4 was done namely, 2.00×10-4M, 1.50×10-4M, 1.00×10-4M, 5.00×10-5M, respectively and is to be place on the spectrophotometer with the unknown and distilled water for the determination of each concentration’s absorbance. As the concentration is proportional with the absorbance of the solution, to determine the concentration of the solution is possible by drawing a graph of concentration against the absorbance. At the end of the experiment, the group found the concentration of the unknown sample is 2.50×10-4M.
Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelength. This measurement can also be used to measure the amount of a known chemical substance. Spectrophotometry is one of the most useful methods of quantitative analysis in various fields such as chemistry, physics, biochemistry, material and chemical engineering and clinical applications. A spectrophotometer is an instrument that measures the amount of photons (the intensity of light) absorbed after it passes through sample solution. With the spectrophotometer, the amount of a known chemical substance (concentrations) can also be determined by measuring the intensity of light detected. In this experiment, we use the spectrophotometer to determine the unknown concentration of potassium permanganate (KMnO4) solution. The approach of this experiment on determining the concentration of the unknown is by finding the absorbance level of the different concentration of the solution. Relating the absorbance level and their respective concentration, we would be able to acquire the concentration of the unknown. The objective of this experiment is to became familiar with typical spectrophotometric analysis and to know the other way on how to know the concentration of a given solution.
II. Review of Related Literature
As stated by Christy P, The spectrophotometer was invented in 1940, by Arnold J. Beckman and his colleagues at National Technologies Laboratories, the company Beckman had started in 1935. They were led by project leader Howard H. Cary. The spectrophotometer was the company's greatest discovery. Before 1940, the chemical analysis process was a long venture taking weeks to complete with only 25 percent accuracy according to the MIT's "Inventor of the Week" archive. In 1940, when the Beckman DU Spectrophotometer was introduced, it simplified the process greatly, requiring only a few minutes for analysis. According to the same source, this test offered 99.99 percent accuracy on the analysis. This instrument set the standard in chemical analysis. A study made by David R. Caprette: A spectrophotometer consists of two instruments, namely a spectrometer for producing light of any selected color (wavelength), and a photometer for measuring the intensity of light. The instruments are arranged so that liquid in a cuvette can be placed between the spectrometer beam and the photometer. The amount of light passing through the tube is measured by the photometer. The photometer delivers a voltage signal to a display device, normally a galvanometer. The signal changes as the amount of light absorbed by the liquid changes. According to David B. Fankhauser, Ph.D., spectrophotometer is an instrument which measures the amount of light of a specified wavelength which passes...
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