Copper In Brass Lab

Spectrophotometric Determination of Copper in Brass
Your Name Here
Partners: his/her name here
Chemistry 1290-xxx
Date Report is Due
TA: TA’s name here

Purpose:
The primary purpose of this experiment was ……
Another purpose of this experiment was ……
Learning about this type of analysis was important in an everyday context because ...

Safety Information:
During this lab nitric acid will be used as an oxidizing agent and (NO2) nitrogen dioxide will form. This gas is extremely toxic, and should not be inhaled. A use of a fume hood should be used during the process of adding nitric acid (HNO3) to the solution. 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 (NO2) are not being removed by the fume hood, an instructor must be notified while the student stops adding the concentrated nitric acid (HNO3). 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 SpectroPro software forceps paper towels wax pencil copper wire steel wool analytical balance brass sample to be tested
80 mLtest tube
250 mL Erlenmeyer flask
50 mL graduated cylinder
250 mL beaker
200 mL beaker
250 mL volumetric flask volumetric pipettes (10mL, 25mL, and 50mL) four 100 mL volumetric flasks
250 mL volumetric flask pipette bulb

Chemicals:
0.2% nitric Acid, HNO3 approximately 50 mL per sample concentrated nitric Acid, HNO3 approximately 50 mL per sample deionized water, H2O approximately 75 mL per sample tap water, H2O approximately 100 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 Spectro 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 (HNO3, 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 absorbance for the spectrophotometer. The direction of the test tube was marked and noted for future use. The student then selected a New Absorbance vs. Concentration experiment in SpectroPro. This was done in order to calibrate the spectrophotometer. The wavelength setting was set on the spectrophotometer at 620nm and the machine was set absorbance, listed as unit (A). The student set the blank to zero absorbance 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 250mL Erlenmeyer flask.
50 mL of concentrated nitric acid was measured in a graduated cylinder, 20 mL of which was transferred to the 80mL 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 (HNO3) was slowly added during the dissolving of the copper wire.
Approximately 75 mL of deionized water was poured into a 250 mL beaker. The nitric acid solution was transferred from the 80mL 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. DI water was added to the mark on the volumetric flask. The flask was stoppered and inverted three times to ensure the solution was
homogenous.
Four 100mL 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. Deionized water was then added to each flask until the solution reached the 100 mL mark.
The absorbance was measured for solutions A to E. The original test tube that was used for the blank setting was rinsed with solution A, filled half full, wiped, and placed into the spectrophotometer for the absorbance 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 absorbance of the unknown and marked the valid range of absorbance on the standard curve.

The following chemical equation represents the reactions that took place during this lab.

Balanced equation(s) goes here.

Data for Copper Dissolution: mass of the copper wire ______ g molarity of solution A ______ M

Solution
Initial Volume of Solution A, mL
Final Volume of Solution, mL
Final Concentration of Solution, M
Absorbance, A
A
------
250.00

B
75.00
100.00

C
50.00
100.00

D
25.00
100.00

E
10.00
100.00

Sample Calculations:

Observations:

Data for Unknown Brass Sample Dissolution:
Unknown number of brass sample _______ mass of the copper wire ______ g

Determination 1
Determination 2
Absorbance, A

Concentration of [Cu(H2O)6]2+ from Beer’s Law Plot, M

Calculated mass of Cu in brass sample, g

Calculated amount of copper in brass sample, % Cu

Average % Cu

Insert standard curve here.

Discussion:

Error of Measurement:

Conclusion:

References: