Crime Lab Essay

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Alex Powell Chemistry Lab 4/5/2012 Crime Laboratory I. In this lab you are finding the concentration of your unknown which isn’t a real blood serum. You are using a visible spectroscopy which is the measurement of the amount of light absorbed by a solution. My hypothesis is that this method is valid and reliable. II. Some materials used in this lab were spectrophotometer cuvettes, test tube rack, pipet, veriner and a spectrophotometer. III. First thing you do is you place seven spectrophotometer cuvettes in a small test tube rack. Make sure you graph along the rigid side because fingerprints on the clear sides can mess up the readings. You then pipet the amounts of material listed in Table 1 of your lab manual, then shake the mixes thoroughly. Turn on you spectrophotometer and set the wavelength dial 540 nm. Allow the instrument to warm up for ten minutes. Then prepare the unknown sample by pipetting 1 ml of the unknown solution into the cuvette and mix with 1 ml of dilute ferric nitrate. Then after that you calculate the concentration for each of the solutions. Cuvette # | 25 mg/dl Standard | H2O ml | Dilute Iron III Nitrate (ml) | .039 M HNO3 (ml) | Concentration | 1 | 0 | 1 | 0 | 1 | 0 | 2 | 0.1 | 0.9 | 1 | 0 | 0.09 | 3 | 0.3 | 0.7 | 1 | 0 | 0.287 | 4 | 0.5 | 0.5 | 1 | 0 | 0.407 | 5 | 0.7 | 0.3 | 1 | 0 | 0.706 | 6 | 1 | 0 | 1 | 0 | 1.316 | When then use the calibration curve to determine the concentration of the unknown and we get .747. IV. As you can see from our data as the amount of H2O decreases and the 25mg/dl standard increases as does our concentration for the salicylic acids. We keep the amount of dilute iron III nitrate the same because it’s our independent variable. With the unknowns concentration we know it falls between .7mbg/dl of standard and only .3 ml of water. My guess is that it’s just higher the .7 because the

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