Additionally, safety goggles should be worn throughout the entire lab. Shoes should be closed toed, clothing should cover legs down to the shoes with socks, and shoulders should be covered by shirts. Hair must be tied back. Caution must be taken during this lab, and if it appears that the fumes from the nitrogen dioxide (NON) are not being removed by the fume hood, an instructor must be notified while the student stops adding the concentrated nitric acid (HON..). It is also possible to stain the hands of those working with these chemicals, so extreme care while transferring solutions that might be highly acidic is a must.
Materials: safety goggles spectrophotometer computer with Spectroscopy software forceps paper towels wax pencil copper wire steel wool analytical balance brass sample to be tested 80 molest tube 250 ml Erlenmeyer flask 50 ml graduated cylinder 250 ml beaker 200 ml beaker 250 ml volumetric flask volumetric pipettes (ml, ml, and ml) four 100 ml volumetric flasks pipette bulb Chemicals: 0. 2% nitric Acid, HON.. Approximately 50 ml per sample concentrated nitric Acid, HON.. Approximately 50 ml per sample denizen water, H2O approximately 75 ml per sample tap water, H2O approximately 1 00 ml per sample
Procedure: During this lab the student turned on and warmed up the spectrophotometer and set the laptop computer up with the program Specter Pro running. The student then obtained the required materials used in this lab and began the procedures. The student cleaned the test tubes with nitric acid (HON.., 0. 2%). One test tube was then filled half full with the same solution of nitric acid and wiped clean of finger prints and smudges. This sample was used as a blank to set the zero absorbency for the spectrophotometer. The direction of the test tube was marked and noted for future use. The student then selected a New
Absorbency vs… Concentration experiment in Spectroscopy. This was done in order to calibrate the spectrophotometer. The wavelength setting was set on the spectrophotometer at Mann and the machine was set absorbency, listed as unit (A). The student set the blank to zero absorbency and finished the calibration of the spectrophotometer. The solution in the test tube was then discarded and the test tube was set aside. Copper wire was obtained, weighed and cut to approximately 2. 5 g, and then cleaned with steel wool. The copper was then handled with forceps, and wrapped tightly around a pencil.
The copper was set aside to prepare the solution used in this experiment. The student placed approximately 100 ml of cold tap water in a mall Erlenmeyer flask. 50 ml of concentrated nitric acid was measured in a graduated cylinder, 20 ml of which was transferred to the ml test tube. This test tube was placed in the Erlenmeyer flask with enough water covering at least 2 CM of the test tube. The coiled copper wire from earlier was cautiously placed into the test tube. The fume hood was lowered to prevent any inhalation of the toxic gas emitted from the exothermic reaction.
The remaining nitric acid (HON..) was slowly added during the dissolving of the copper wire. Approximately 75 ml of denizen water was poured into a 250 ml beaker. The nitric acid solution was transferred from the ml test tube to the water in the beaker. The solution changed from dark green to bright blue. After the solution cooled, it was transferred to a clean 250 ml volumetric flask. The test tube that contained the nitric acid solution was rinsed and those rinses were also added to the volumetric flask. Del water was added to the mark on the volumetric flask.
The flask was stopper and inverted here times to ensure the solution was homogeneous. Four mall flasks were used during the dilution of the copper solution. Each was labeled from B to E. Volumetric pipettes were used to transfer the original nitric acid solution, now considered solution A, to each of the flasks. Flask B contained 75 ml of solution A, flask C contained 50 ml of solution A, flask D contained 25 ml of solution A, and flask E contained 10 ml of solution A. Denizen water was then added to each flask until the solution reached the 100 ml mark. The absorbency was measured for solutions A to E.
The original test tube that was used for the lank setting was rinsed with solution A, filled half full, wiped, and placed into the spectrophotometer for the absorbency reading. The same procedure was repeated for solution B, C, D, and E. A standard curve was prepared and printed for later use. Following the completion of the dissolution of copper wire, an unknown brass sample was dissolved and analyzed as previously done with the copper wire. Students plotted the absorbency of the unknown and marked the valid range of absorbency on the standard curve. The following chemical equation represents the reactions that took place during this lab.