HShin_Lab_Report_8

HShin_Lab_Report_8 - Author: Hoon Shin, Austin Kwon,...

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Author: Hoon Shin, Austin Kwon, Branden Heilman Group: F TA: Eileen Chen Section: A05 Class: Chem100A, UCSD (University of California San Diego) Date: 6/08/08 Atomic Spectrometry Abstract The purpose of this lab was to calculate the concentration of calcium in Cereal, Cheerios, and fruit juice which was provided by lab. This can be done by using the flame spectrophotometery where possible for measuring the emission and absorbance which can be used to create the calibration curve to obtain concentration of calcium in cereal and fruit juice. As a results, concentration of Calcium in cereal was determine to be 16.747µg/mL ± 2.838µg/mL when “Two-Increment standard addition method”(described in introduction) was used. When the Multiple-increment standard addition method was used, the concentration of calcium in cereal was 13.37333µg/mL ± 0.18913µg/mL. Calcium concentration in fruit juice was 160.4422ppmCa in 5mL. Introduction Part 1 – Calcium concentration of dry cereal First step of this experiment requires one to turn certain amount of cereal into ash in the 200˚C oven which will be used as unknown solutions. By adding acid, HCl, oxalate solid will be removed and remains only the ions of calcium. In this particular experiment, two method of finding the concentration of calcium in cereals are introduced; two-increment standard addition method and multiple increment standard addition. Two-increment standard addition method is to make two different solutions where one is “unspiked” and the other one is “spiked” solution which contains known amount of
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calcium. With these solution made and absorbed absorptions of each of the solutions, one can use the equations to find the concentration of the sample. Where Csam, Asam, Cstd, and Asam+std equals concentration of the sample, absorbance of the sample, concentration of the standard solution, and absorbance of the spiked solution, respectively. The other method to find the concentration of calcium is by “multiple-increment standard addition”. By plotting the absorbance calibration curve of the concentrations of known standard solution and unknown solutions, one can easily determine the concentration in a sample. Where the formula: All the plotted points can be obtained using the spectrometer. Part 2 – Calcium concentration in fruit juice. Line spectra can be observed when the electron leaves the element from the heat. These energy emissions are visible around the ultraviolet region. The calcium can be found due to the constant of the emission proportional to the calcium concentration. CaCl 2 (s) → CaCl 2 (g) → Ca(g) + 2Cl(g) Considering the equation above, all the gas state atoms can be drop back to the ground state which gives: ( 29 λ hc/ hv Ca(g) ) ( Ca Ca(g) * + → g In reading the emission, some of the ions will lose an electron. Since KCl and NaCl takes less energy to ionize, this too will be considered as radiation buffer.
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This figure is how the emission is measured by the flame.
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HShin_Lab_Report_8 - Author: Hoon Shin, Austin Kwon,...

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