to make a penny became higher than the actual face value. So pennies started being produced with 2.5% copper coating by mass with a core that contains primarily zinc metal. Using this information one can hypothesize that these pennies will have close to 2.5% copper because in this experiment only pennies minted after 1982 were used. Also one may hypothesize that pennies with scratches or cuts may have less percent of Cu because the copper is on the surface. METHOD: First the solution was prepared. The standard solution was prepared first to use for the calibration of the spectrometer. Six solutions of this type were made in 50mL volumetric flasks. These solutions contained 10.00, 8.00, 6.00, 4.00, 2.00 and 0.00mL of stock Cu 2+ solution. 3mL of 15 Molar ammonia solutions was then added to all 6 solutions and then each solution was filled to the 50mL mark with distilled water. Next the penny samples were prepared. Three pennies were placed in three separate 150mL beakers. Each penny was then dissolved by adding 25mL of 6 Molar HNO 3 to the beakers. This reaction took about 10 minutes. The dissolved penny solution was then added to 100mL volumetric flasks by the method of quantitative transfer. 14mL of concentrated ammonia solution was then added to each flask. 1mL of ammonia was again added until no solid remained. The volumetric flask was then diluted to volume. 2
Next absorbance was measured. Cuvettes were filled about 75% full with each of the six standard solutions and the three penny solutions. Next, a calibration curve was created using the spectrometer. The 0.00mL Cu 2+ solution was used to find the wavelength needed in the curve, which tells the spectrometer what wavelength of light to pass through the solution. The maximum wavelength used to find the absorbencies was 606 nm. Then the five standard solutions were used to create the curve. Lastly, the calculations are made. The concentration of Cu 2+ solution in each standard solution was the first thing calculated. To calculate this, the volume of Cu 2+ solution is multiplied by the density of Cu 2+ solution and then divided by the total volume of standard solution. The equation of the calibration curve was the next calculation. This was completed using the linear regression in loggerpro. Using this equation and the
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- Fall '08