Detection of Organic Molecules in Unknowns

Biology Lab Report 30 October Detection of Organic Molecules in Unknowns Introduction The Beer Lambert’s law illustrates that the amount of light conveyed through a solution is related to the concentration of the substance (Beer-Lambert Law). Therefore, the concentration of substances can be determined by measuring the amount of absorbed light using spectrophotometry. This experiment aimed at finding the concentrations of unknown substances using varying concentrations of standard solutions.MethodsFive different starch concentrations ranging from 0 to 100 µm/ml were prepared to make a total volume of 2 ml. The concentrations of the solutions were determined using spectrophotometry by measuring the absorbance of the solutions, which was recorded. The absorbance values of the three unknown samples were also determined and recorded.ResultsFigures and TablesCalibration CurveFigure 1: Calibration curve for the standard solutions. The absorbance of the standard solutions was plotted against the concentrations in µl/ml. The best line of fit and the equation of the line were also determined. Table 1: Absorbance of Unknown SolutionsSolutionAbsorbanceUnknown 10.583Unknown 20.461Unknown 30.210Concentrations of unknown solutionsThe concentrations of the unknown solutions were obtained by substituting their absorbance values in the equation of the calibration curve.Y=0.0101x +0.0005 where y was equal to the absorbance a 580 nm and x was equal to the concentration in µl/ml.For unknown 1, 0.583=0.0101x+ 0.00050.583-0.0005=0.0101×0.5825=0.0101×57.6733=xTherefore, the concentration of unknown 1=57.67 µl/ml.Following the same procedure, the concentrations of unknown 2 and 3 were 45.59 and 20.74 µl/ml.DiscussionIt was observed that the absorbance of the solutions increased with an increase in the concentrations. Substitution of the absorbance values of the unknown into the equation of the standard curve enabled the determination of the concentrations of the unknown samples. Therefore, it was concluded that spectrophotometry is a reliable and efficient method of determining the concentrations of unknown substances provided that a calibration curve is provided.Works CitedBeer-Lambert Law 2010. Web. 30 Oct. 2014. .

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