Experiment 2 - Experiment 2 Introduction Organic phosphates...

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Experiment 2 Introduction Organic phosphates are essential in the role and the survival of biological systems, making them highly sought after all over the world. It is often a limited nutrient in many biodiversity’s, and its availability especially within freshwater environments governs the rate of growth of organisms. Though phosphate may increase the rate of growth in organisms, in high concentrations it can also have significant ecological consequences. For example, the increased growth rate may cause a devastating effect on an aquatic ecosystem through oxygen depletion. It is therefore imperative to monitor phosphate within individual environments, especially freshwater systems. Determining the phosphate in water samples can be carried out by spectrophotometry. Most commonly used standard method is based on the spectrophotometric determination of phosphorous molybdite blue also known as the ascorbic acid reduction method. The reason why spectrophotometry can be employed as an analytical tool is due to the amount of light absorbed within a solution which is directly proportional to the concentration of the species in the solution by the combined Lambert beer law. = A εCl ( ) 1 Therefore based on Lambert-Beer law, a plot of absorbance, A, versus molar concentration, at constant path length would yield a linear relation; an external calibration method can be used using known concentrations as standards to determine unknown concentrations within the standard concentration range. The ascorbic acid reduction method, produces an intensely blue-coloured phosphorous molybdenum blue compound by the reaction shown below; [P(Mo3O10)4]3- + 3H+ + Ascorbic Acid (MoO2•4MoO3)2•H3PO4 + 2MoO2 + Dehydroascorbic acid + 4H2O The rate of colour development as well as final intensity is dependent on reaction time and temperature. Therefore the variables must be kept as constants during the analysis. The blue colour may develop slowly and incompletely if the temperature is below 20°C for a time period of 20-30 minutes. This experiment is aimed to determine the concentration of phosphate ions in a freshwater sample using UV-Visible spectrophotometry, with the ascorbic acid reduction method. Through the use of these techniques we will gain not only an understanding of both the importance of phosphate and its chemistry but also experience and appreciation for analysis of real-life samples. Method: The analysis of phosphorous in the water sample was carried out in three separate parts. Part one involves the preparation and analysis of 6 standards. The calibration standards were prepared by Experiment 2 Michael Howden CBMS308
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accurately pipetting volumes of 0, 1, 2, 4, 7 and 10 mL of diluted dihydrogen phosphate stock solution (concentration) into a series of 50 mL volumetric flasks and then 30 mL of distilled water
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This note was uploaded on 04/27/2011 for the course SCIENCE 02 taught by Professor Apfd during the Spring '10 term at Alabama.

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Experiment 2 - Experiment 2 Introduction Organic phosphates...

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