Download Chemical Transformations of Copper and more Lecture notes Metallurgy in PDF only on Docsity!
Chemical Transformations of Copper
Introduction:
Copper was one of the first metals to be isolated, due to the ease of separating it from its ores. It is believed that the process was known ( metallurgy ) as early as 4500 BC. It is a ductile, malleable metal and is easily pounded and/or drawn into various shapes for use as wire, ornaments and implements of various types. Alloys of copper (bronze, brass) were discovered quite early in history and were among the first impetuses for international trade. Pure copper is the best electrical conductor of the more abundant metals. It has a good thermal conductivity and is corrosion resistant. Copper as a metal is second in commercial importance only to iron. In this experiment, a weighed amount of copper metal is transformed, through a series of reactions, into other copper-containing compounds, and is eventually returned to the metal state. The series involves the use of reactions classified as metathesis, decomposition, displacement and oxidation-reduction reactions. The following equations (unbalanced) outline the series of transformations to be performed:
A. Cu (s) + HNO3 (aq)! Cu(NO3)2 (aq) + NO2 (g) + H2O (l)
B. Cu(NO3)2 (aq) + NaOH (aq)! Cu(OH)2 (s) + NaNO3 (aq)
C. Cu(OH)2 (s)! CuO (s) + H2O (l)
D. CuO (s) + H2SO4 (aq)! CuSO4 (aq) + H2O (l)
E. CuSO4 (aq) + Zn (s)! Cu (s) + ZnSO4 (aq)
This series of reactions begins and ends with copper metal. Since no copper is added or removed between Reactions A and E, and since each reaction nearly goes to completion, you should be able to quantitatively recover all the copper metal you started with. The sequence of reactions also shows the wide variety of colors observed for inorganic compounds.
Experimental Procedure:
Part A: Preparation of Copper(II) Nitrate Solution
Place about 100 mg of copper wire (about 1 cm of 18 gauge wire), weighed to the nearest mg, in a 10 mL beaker. In the HOOD , add 2 mL of 6M nitric acid to the beaker and warm the contents on a hot plate. Continue heating until the copper wire has completely dissolved and the evolution of brown fumes of nitrogen dioxide is no longer observed. If necessary, you may cautiously add more nitric acid in 2 mL increments, but only add sufficient nitric acid to complete the reaction. Avoid adding a significant excess. The nitrogen dioxide should appear as a brown haze over the surface of the solution. Allow the resulting blue solution of copper(II) nitrate to cool to room temperature. This cooling process may be hastened by placing the beaker cautiously in an ice bath for a few minutes. When the solution has cooled, add 2 mL of distilled water to the blue solution.
Part B: Preparation of Copper(II) Hydroxide
Add a magnetic stirring bar to the beaker and place the flask on a microscale magnetic stirrer. At room temperature, with stirring, carefully add 6M NaOH solution dropwise until the solution is basic to red litmus paper. Use a capillary tube to remove sample for pH testing. A light blue precipitate of copper(II) hydroxide is formed as this reaction is carried out. Make sure the litmus paper has actually changed from red to blue, rather than simply being colored blue by the blue precipitate.
Part C: Preparation of Copper(II) Oxide
Set the hot plate for a moderate heat setting, and while stirring heat the beaker using a
temperature of 110o-115oC. A setting of 3 on most hot plates will work. If a reaction has not occurred after 5 minutes, turn up the heat.
During this time, the copper(II) hydroxide is transformed into copper(II) oxide (or cupric oxide), which appears as a black precipitate. When no more blue precipitate is present, allow the mixture to cool to room temperature and remove the magnetic stirring bar using forceps. If necessary, rinse the bar with a small amount of water, collecting the rinse in the beaker. Isolate the black solid by suction filtration using a Hirsch funnel. Rinse the beaker with 1 - 2 mL of
NOTE: T his reaction should be carried out in a well-ventilated area
(preferably a hood).
NOTE: Stirring is essential to prevent bumping of the mixture and
thus loss of CuO.
Data Sheet
Name _____________________________________________ Section _____________
Chemical Transformations of Copper
- Initial mass of copper wire __________________________________________
- Mass of Copper + weighing paper ____________________________________
- Mass of weighing paper ____________________________________
- Mass of copper recovered ____________________________________
- Percentage recovery (show calculation) ______________________________
- In Part E of the experiment, the zinc metal is added to undergo a redox reaction with the copper(II):
Zn + Cu+2^! Cu + Zn+
Hydrogen gas is also generated in this step. How is the hydrogen gas formed?
- Why is a large excess of zinc added in the reaction of Part E?
PRESTUDY
Name _______________________________________________ Section ____________
Chemical Transformations of Copper
1.(4 points) The first reaction in today's experiment follows the following balanced equation:
Cu(s) + 4HNO3 (aq)! Cu(NO3)2 (aq) + 2NO2 (g) + 2H2O
The remaining 4 reactions follow the following equations: Balance each of these:
A. Cu(NO3)2 (aq) + NaOH(aq)! Cu(OH)2 (s) + NaNO3 (aq)
B. Cu(OH)2 (s)! CuO(s) + H2O
C. CuO(s) + H2SO4 (aq)! CuSO4 (aq) + H2O
D. CuSO4 (aq) + Zn(s)! Cu(s) + ZnSO4 (aq)
2.(4 points) Classify the above 4 reactions as to type: (substitution, decomposition, etc.)
3.(2 points) Based on the balanced equations of Question 1, if you used 85.0 mg of copper in the initial reaction, calculate the exact amount of zinc required to complete the reaction in equation D.
