Formal Chem Lab #1 (Penny) - Copper Concentration in...

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Copper Concentration in Pennies Paige Ferland CHM 144M Dr. Danielson TA: Fan Connor English, Andrew Garcia 11/14/13 Methods: Solution Preparation Standard Solutions: A 5.00 g/L stock Cu2+ solution is provided and around 40mL of this solution needs to be collected in the beginning of the lab. Obtain 6 50mL volumetric flasks in which to hold the dilutions of the stock solution. 0.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL, and 10mL of stock solution are pipetted into the six flasks respectively (make sure they are labeled). While the flasks are under the fume hood, 3mL of concentrated ammonia (15 M) is added to each solution, the flask 1
is then filled to the line with distilled water and the six standard solutions are prepared. The concentration of each of the flasks should be calculated and recorded and two cuvettes obtained for use during the spectrometric analysis. Penny Solutions: Each student should have their own penny and from that penny create their own solution. The penny is weighed and the mass recorded in the notebook. The age of the penny should also be written down as this pertains to the hypothesis of the lab. In the fume hood, place the penny in a 150mL beaker and add 25mL of 6 M HN O 3 (measure using a graduated cylinder). The reaction should go to completion, when there is no solid left in the beaker. The beaker should then cool for around 10 minutes. While still in the fume hood, all the contents from the beaker should be quantitatively transferred using a funnel and distilled water to make sure there is no loss of sample. Use 5-10mL to rinse the beaker and empty into the flask, repeat this step two more times emptying into the flask before the next rinse. With flask still in fume hood, add 14mL of concentrated ammonia to the flask using a graduated cylinder. A blue color should develop; swirl to dissolve any solid left over. Dilute flask with distilled water, stopper, and invert to mix thoroughly. Absorbance Measurement Before measuring the absorbance of the standard solutions or the penny solutions it is necessary to determine the wavelength of maximum absorbance from a MeasureNet photodiode array (PDA) spectrophotometer. By looking at the given spectrum within the range of 350 to 850 nm (200-350nm is caused by the absorbance of light from the plastic cuvette and therefore, is not taken into account) the maximum wavelength value can be determined as the highest peak. Since the stock solution and the dilutions are blue in color the peak wavelength should correspond to the red LED color, as both blue and green would be reflected.

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