Methods: Preparation of Standard Solutions:Put 0.00 mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL, and 10.00 mL of the copper stock solution into separate 50 mL volumetric flasks. Add 3 mL of ammonia to the solution and mix with distilled water. Then calculate the concentrations of the copper in each of the six standard solutions. Preparation of Penny SamplesGet three pennies and weigh each penny and record the mass in your notebook. Note the age and the condition of the penny in your notebook. Do not confuse which mass goes with which penny. In the fume hood place the penny in a 150mL beaker and add 25mL of 6M HNO3 . Let the reaction proceed in the fume hood until the entire penny has dissolved. The let it sit in the fume hood for another 10 minutes. Transfer the beakers contents into a 100mL volumetric flask. Make sure all of the sample's contents is transferred, so rinse the beaker with a small amount of distilled water. Still in the fume hood add 14mL of concentrated ammonia solution to the volumetric flask and swirl to develop a blue color. If the light blue solid remains add more concentrated ammonia solution 1mL at a time and invert to mix thoroughly. Fill the cuvette for each penny sample and label the lid. There should be a total of 3 cuvettes with each penny sample. Measurement of AbsorbanceThe spectrometer along with the Lab Quest were used to find the calibration curve, maximum absorbency, and the absorbency of the stock solution and the pennies. Put the 0.0 cuvette into the spectrometer. Then the most concentrated solution was put
into the spectrometer and the wavelength was recorded. Add the cuvettes from most concentrated to least concentrated. CalculationsTo calculate the concentration of the stock solutions the following equation was used, where M is molarity and V is volume.
- Fall '08
- Chemistry, pennies, Stock Solutions