COMPOUNDS OF COPPER
The purpose of this experiment is to illustrate some kinds of chemical reactions, using copper and its compounds as examples. You will dissolve some copper in nitric acid and, after forming several different compounds, obtain the copper back again in the free state. The type of reaction will be indicated; you will write the equation for each reaction. This experiment also provides practice with some standard laboratory procedures. With good laboratory technique, you should be able to recover about 95% of the mass of the copper originally dissolved in the nitric acid.
1. Oxidation-Reduction
Weigh about one gram of copper on a watch glass on the balance. If wire is used, clean it with steel wool. Place the copper in a 250 mL beaker and add 5 mL of 35% sulfuric acid. (Any reaction?) Gently warm the beaker over a Bunsen burner. Do not permit it boil! Note if any reaction occurs. If no reaction occurs, pour the sulfuric acid off the unreacted copper.
Add 2 mL of concentrated nitric acid and allow the copper to dissolve. (Caution!! Do this in a hood and be careful handling the nitric acid!) Do not breathe the red-brown fumes of nitrogen dioxide, NO
2
.
Continuous exposure to these fumes can cause pulmonary edema (fluid in the lungs which causes drowning).
If the material in the beaker congeals to a solid mass, add 2 -3 mL of distilled water to dissolve the solid. If the copper does not all dissolve, the solution may be warmed gently and a few more drops of nitric acid may be added.
When the copper is dissolved, add 70 mL of distilled water and take the beaker back to your bench area.
1. Oxidation-Reduction – Alternate!
Weigh about one gram of copper on a watch glass on the balance. If wire is used, clean it with steel wool, bend into a flat coil place it in the bottom of a completely-dry 250-mL beaker. Pour approximately 20 mL of a mixture of a hydrogen peroxide-sulfuric acid solution (1 part water, 2 parts 30% H
H
2
SO
4
2
O
2
, 2 parts 6 M
by volume) into the beaker so as to completely cover the copper coil. Cover the beaker with a dry watch glass and place it in a 400-mL beaker containing 150 mL water heated to 60 degrees Celsius or warmer. This will serve as a hot-water bath to speed up the oxidation reaction. Keep the 250-mL beaker in the hot-water bath for only three minutes, then remove it and dry the outside with a paper towel. Swirl the beaker gently until all the copper is oxidized, producing the solution of aqueous copper(II) sulfate.
When the copper is dissolved, add 70 mL of distilled water and take the beaker back to your bench area.
2. Precipitation
Add 15 mL of 6M sodium hydroxide to the solution of copper (II) nitrate obtained in step 1. Make sure that the solution is basic by testing with litmus paper. If the solution is not basic, add additional 2 mL increments of sodium hydroxide until the solution is basic. Note the precipitate of copper (II) hydroxide .
3. Dehydration
Set the beaker containing the precipitated copper (II) hydroxide on a wire gauze supported on a tripod.
With constant stirring, heat almost to a boil. If the solution is not properly stirred severe bumping can occur causing the solution to spatter! The copper (II) hydroxide, a gelatinous precipitate changes to a more granular copper (II) oxide. The mixture should thin out and turn to a dark brown or black suspension. Filter the solution, collecting the dark copper (II) oxide on the filter paper in the funnel.

General Chemistry Compounds of Copper
4. Dissolution
Replace the beaker under the filter funnel with a fresh, clean 250 mL beaker. Dissolve the copper (II) oxide by adding 15 mL of 3 M sulfuric acid directly to the filter paper containing the oxide residue. Allow the acid solution to drain through the funnel into the 250 mL beaker. If all the oxide residue does not dissolve, pour the acid solution through the filter paper and collect it again. This process can be repeated until all the residue is dissolved. Rinse the filter paper with two 10 mL portions of cold distilled water and collect the rinse water in the beaker with the acid solution. If necessary, rinse with more cold water until the filter paper is no longer tinged blue.
5. Displacement
Add about 1.5 grams of powdered zinc to the copper (II) sulfate solution obtained in step 4. If bubbles do not form quite actively in the beaker, add 10 - 15 drops of 3M sulfuric acid. Note the formation of the red-brown elemental copper and the disappearance of the characteristic blue copper of the copper (II) ion solution.
Patience is required at the step. Adding a large excess of zinc may decolorize the solution quickly, but the gain is lost by the time required to dissolve the excess zinc. Gently shake the solution or use a magnetic stirrer to keep the zinc well mixed with the copper (II) sulfate solution. After the blue color is gone from the solution, any excess zinc left can be separated from the copper residue by decanting (pouring off) the liquid and dissolving the zinc with 5 mL dilute (6 M) hydrochloric acid.
Weigh a piece of filter paper. The elemental copper can be isolated and dried by filtration. Use the weighed piece of filter paper. Wash with cold water, and then with two 10 mL portions of acetone. When dry, the copper can be weighed and percentage recovery calculated.
DATA
Step 1
Mass of watch glass and copper, g
Mass of watch glass, g
Mass of copper used, g
Step 5
Mass of filter paper and copper, g
Mass of filter paper, g
Mass of copper recovered, g
_______________
_______________
_______________
_______________
_______________
_______________

General Chemistry Compounds of Copper
CALCULATIONS
Percent Cu recovered = (mass of copper recovered – Step 5/ mass of copper used – Step 1)x100
Percentage of copper recovered _______________
EQUATIONS
Please write balanced equations for all reactions in this experiment
Oxidation-Reduction
Precipitation
5.
6.
Dehydration
Dissolution
Displacement of the copper
Displacement of the excess zinc