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 by oxidizing it with hydrogen peroxide (H2O2) 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 original copper sample.
Pre-Laboratory Exercise:
1. Search on-line for a material safety data sheet (MSDS) for the 30% hydrogen peroxide solution you will
be using in step 1 of this experiment. There are several sources of MSDSs online that are free of charge.
2. Download a copy of the MSDS and save it to either your computer or a removable storage device.
3. Prepare a MSWord document explaining in your own words the hazard associated with concentrated
hydrogen peroxide solutions. Insert a copy of the MSDS into the document and save it using the name
perox_MSDS_AB where AB represents the first and last initials of your name.
4. Be prepared to submit this document as instructed by your laboratory instructor.
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, 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% H2O2, 2 parts 6 M
H2SO4 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 ºC 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.
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.
General Chemistry
Compounds of Copper
5.
Displacement
Add about 0.5 grams of magnesium turnings 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 magnesium may decolorize the solution
quickly, but the gain is lost by the time required to dissolve the excess magnesium. Gently shake the
solution or use a magnetic stirrer to keep the magnesium well mixed with the copper (II) sulfate solution.
After the blue color is gone from the solution, any excess magnesium left can be separated from the copper
residue by decanting (pouring off) the liquid and dissolving the magnesium with 5 mL dilute (6 M)
hydrochloric acid. Be sure to properly dispose of the liquid as instructed.
Wash the solid residue in the beaker with two 20 mL portions of deionized water. Allow the solids to
settle and decant away the liquid after each washing. In the hood, carefully add small amounts of 6 M HCl
to dissolve any magnesium remaining in the residue. If bubbling stops, but silvery magnesium metal is still
present, add 1-2 more drops of the 6 M HCl.
Allow the copper granules to settle, and then decant away the supernatant liquid, again disposing of the
liquid as instructed. Wash the copper granules with 25 mL of warm deionized water. Quantitatively transfer
the solid copper to a pre-weighed watch glass using a rubber policeman and a wash bottle. Carefully pour
most of the water from the watch glass.
To dry the copper, place the watch glass over the mouth of a beaker that is half full of tap water. Heat
the water to boiling, in order to steam dry the copper residue. Stop heating as soon as the metal appears to be
dry, in order to avoid oxidizing the metal.
Allow the watch glass and copper to cool on a paper towel. Then weigh them carefully. To see whether
the copper is completely dry, heat the watch glass and copper for 4 more minutes on the steam bath.
Remove, cool and reweigh. Continue heating and weighing until the mass remains constant to within 5 mg.
DATA
Step 1
Mass of watch glass and copper, g
_______________
Mass of watch glass, g
_______________
Mass of copper used, g
_______________
Step 5
Stable mass of watch glass and recovered copper, g
_______________
Mass of watch glass, g
_______________
Mass of copper recovered, g
_______________
CALCULATIONS
Page 2
General Chemistry
Compounds of Copper
Percent Cu recovered = (mass of copper recovered – Step 5/ mass of copper used – Step 1)x100
Percentage of copper recovered
_______________
Page 3
General Chemistry
Compounds of Copper
EQUATIONS
Please write balanced equations for all reactions in this experiment
1.
Oxidation-Reduction
2.
Precipitation
3.
Dehydration
4.
Dissolution
5.
Displacement of the copper
6.
Displacement of the excess magnesium
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