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Determination of Concentration of Chromium

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chemistry lab report
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  ABSTRACT INTRODUCTION Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. Chromium does not occur freely in nature. The main chromium mineral is chromite. As was mentioned earlier, chromium compounds can be found in waters only in trace amounts. The element and its compounds can be discharged in surface water through various industries. It is applied for example for metal surface refinery and in alloys. Stainless steel consists of 12-15% chromium. Chromium metal is applied worldwide in amounts of approximately 20,000 tons per year. It may be polished and it does not oxidize when it comes in contact with air. Chromium may be present in domestic waste from various synthetic materials. Through waste incineration it may spread to the environment when protection is insufficient. AIMS THEORY Chromium that is deposited on highroads srcinated from brake and dusts and exhaust of automobile engine can unfavourably permeate into any water straems nearby via flowing rainwater. Lakes and water streams which is nearer a typical congested with automobiles areas are the most susceptible areas to be contaminated by such chromium. Due to its cancer-risk character and toxicity even at mere concentrations, a lot of federal environmental agencies are doing researches to determine its presence in many environmental samples. Thus, in this experiment absorption spectroscopy will be used to detect the concentrations of Chromium (VI) in a water sample. Absorption spectroscopy operates on the measuring principle of light. Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies  as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum. Absorption spectroscopy measuring priciple of light before and after it passes through an aqueous metal solution. The amount of light absorbed by the chemical species in the sample is equivalent to the difference in the amount of light before it enters the sample and after it exits the sample. For the purpose of light to be absorbed by chemical species, the light must be set to a specific wavelength. Every chemical species absorbs distinct wavelengths of light. In absorption spectroscopy, the wavelengths of light absorbed by the in solution are detected. In this experiment, standard stock solutions are prepared by diluting 300 parts per million (p.p.m) of Chromium (VI) standard solution Five standard stock solutions being prepared from the concentrated Chromium (VI) standard solution with range from 15 p.p.m to 300 p.p.m. To calculate the dilute solutions volume needed, the solution dilution formula can be used: M 1 V 1 =   M 2 V 2 M 1 : is a concentration of standard Chromium (VI) solutions, which is 300 p.p.m. V 1 : is volume of distilled water needed to dilute Chromium (VI) solutions M 2 : is a concentration of stock solution of Chromium (VI) solutions, which are 15, 45, 75, 150 and 300 p.p.m. V 2  : is a volume of volumetric flask which is 50mL Quantitative analysis using spectroscopy is based on Beer-Lambert Law. Beer-lambert Law states that absorbance value depends on total quantity of the absorbing compound in the light path through the cuvette. Thus, if we plot a graph of absorbance versus concentration of the compound solution, we get a straight line passing throught the srcin. A compound w ith high molar absorbance is very effective at absorbing light. Hence, low  concentrations of a compound and high molar absorbance can be easily detected by the spectroscopy.The Beer-Lamberts Law A = εLC  A : is absorbance value from the spectroscopy ε : molar absorbance (L/mol.cm)  L : path length of the cuvette in which the sample is contained C : Concentration of the compound in solution (mol/L) APPARATUS & MATERIAL PROCEDURES RESULT & CALCULATION DISCUSSION CONCLUSION RECOMMENDATION REFFERENCE APPENDIX
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