Recovery of Elemental Copper from Copper (II) Nitrate
Objectives:
Students should be able to…
- recognize evidence(s) of a chemical change
- convert word equations into formula equations
- perform a series of chemical reactions in order to recycle
the element copper
- determine the percent recovery of elemental copper
Challenge:
How good and accurate a chemist are you? Given a
solution of Cu(NO3)2, what percentage of elemental copper
can you recover from the original solution?
Materials:
1 M copper (II) nitrate
2 M sodium hydroxide
250 or 400 mL beaker
Distilled water
Bunsen burner
Al wire, 18 gauge or heavier
pH paper
Goggles
3 M hydrochloric acid
600 mL beaker
Ice water
Stirring rod
Ring stand
Graduated cylinder
Watch glass, 90 mm
Acetone
Procedures:
Conversion 1:
THIS IS ALREADY COMPLETED FOR YOU!!!
Copper reacts with nitric acid to produce a brownish-orange gas called nitrogen
dioxide. The blue color of the solution is characteristic of many copper
compounds dissolved in water. You will be provided with 25 mL of 1 M solution
of copper (II) nitrate. This solution contains 1.6 grams of copper. Since the
brown nitrogen dioxide produced by the reaction is toxic, I have prepared this
solution in advance for you.
Conversion 2:
CONVERTING COPPER (II) NITRATE TO
COPPER (II) HYDROXIDE
1.
Obtain 25 mL of copper (II) nitrate
2.
Test the copper (II) nitrate solution with pH paper. DO NOT DIP THE
PAPER INTO THE SOLUTION!!! Instead, take your clean stirring rod and
dip into the solution. Carefully touch the pH paper with the tip of the
stirring rod. Record the pH results in your data.
3.
Obtain 25 mL of 2 M sodium hydroxide and also test it with pH paper
using the same method as stated above. Remember that a pH less than 7
indicates an acid…pH greater than 7 indicates a base…pH equal to 7
indicates a neutral solution. Record your results.
4.
Fill your 600 mL beaker one third full of ice water. Carefully place your
beaker containing the copper (II) nitrate solution inside the 600 mL beaker
so that the beaker floats in the water.
5.
Slowly and cautiously add small portions of the sodium hydroxide
solution to your copper (II) nitrate solution in the smaller beaker.
Continuously mix the solution with a gentle swirling motion. Proceed until
all 25 mL of the sodium hydroxide solution have been added. This
neutralization process produces considerable heat, so stir well and add
the sodium hydroxide solution SLOWLY!
6.
Test the resulting solution with pH paper. If the test paper does not match
the original color of the basic sodium hydroxide, add more sodium
hydroxide to the 400 mL beaker while mixing until the color matches. The
pale blue solid, termed a precipitate, is copper (II) hydroxide. The liquid
which remains is sodium nitrate. Record your results.
Conversion 3:
CONVERTING COPPER (II) HYDROXIDE TO
COPPER (II) OXIDE
1.
Add 50 mL of distilled water to the beaker containing the copper (II)
hydroxide precipitate. Heat to a gentle boil and stir until all the material is
converted to a brown-black substance. This substance is copper (II)
oxide.
2.
Remove the stirring rod from the beaker. Let the beaker and the solution
cool for 5 minutes.
3.
Pour off the extra liquid (don’t lose any solid!!) Wash the precipitate
remaining in the beaker by adding 100 mL of distilled water and stirring
gently. Let the precipitate settle for another 5 minutes and pour off the
wash water, again leaving all solid particles in the beaker. This process is
called decanting.
Conversion 4:
1.
CONVERTING COPPER (II) OXIDE TO COPPER
(II) CHLORIDE
Add 25 mL of 3 M hydrochloric acid to the black copper (II) oxide in the
beaker. Stir gently or cover with a watch glass and swirl gently. The
oxide will dissolve in a minute or two…leaving a clear, aqua blue solution
(the result of the formation of copper (II) chloride).
Conversion 5:
CONVERTING COPPER (II) CHLORIDE BACK TO
COPPER METAL
1.
Add at least 1.5 grams of aluminum wire (~ 75 cm) to the copper (II)
chloride solution. (Cut the wire and bend it in half; bend it again until it is a
bit longer than a stirring rod. The bend it to form an “L” shape that will fit
in the beaker so that a “handle” remains above the solution level.)
2.
Immediately cover the beaker with a watch glass and allow it to stand.
Watch what happens and record your observations.
3.
As the aluminum wire “grow copper hair,” shake the wire gently to
dislodge the copper. Cover and let the beaker stand overnight.
Recovering Elemental Copper
1.
Heat 200 mL of distilled water to a boil.
2.
Remove any remaining aluminum wire from the beaker; with forceps
remove any small bits of wire mixed in with the solid copper.
3.
Decant and discard the clear liquid.
4.
Wash the copper in the beaker twice with 50 mL portions of the hot
distilled water…stir and let settle…decanting the wash water each time.
Try not to lose any of the solid copper.
5.
Weigh a clean watch glass to the nearest 0.01 g. Record the mass. Swirl
the copper and remaining water in the beaker and quickly pour it onto the
watch glass.
6.
With a distilled water wash bottle, gently wash any remaining copper from
the beaker into the watch glass. Allow the copper to settle and carefully
pour off the excess water from the watch glass.
CAUTION: Acetone is extremely flammable. For the next step of the
experiment, be sure all burner flames are extinguished in the lab before
proceeding!
7.
Wash the copper on the watch glass with a small quantity of acetone (the
amount will depend upon the size of the watch glass).
8.
Pour off the acetone into a small beaker, being very careful not to lose
acetone as before.
9.
Wash the copper with a second portion of acetone and pour off the
acetone as before.
10.
After the second wash, allow the copper and watch glass to stand
overnight in the fume hood until dry.
Recovery of Elemental Copper
Report Sheet
1.
Initial mass of copper (given)
2.
Mass of copper and watch glass __________
3.
Mass of watch glass
__________
4.
Mass of recovered copper
__________
5.
Percent yield (show calcs!)
__________
Mass of recoverd copper
Initial mass of copper
6.
__________
x 100
Write and balance the formula equation for Conversion #1:
copper + nitric acid  copper (II) nitrate + nitrogen dioxide + water
7.
Write and balance the formula equation for Conversion #2:
copper (II) nitrate + sodium hydroxide  copper (II) hydroxide + sodium
nitrate
8.
9.
Describe the color of the pH paper when in contact with:
a.
copper (II) nitrate solution ________________________________
b.
sodium hydroxide solution ________________________________
Write and balance the formula equation for Conversion #3:

copper (II) hydroxide  copper (II) oxide + water
10.
Write and balance the formula equation for Conversion #4:
copper (II) oxide + hydrochloric acid  copper (II) chloride + water
11.
Write and balance the formula equation for Conversion #5:
copper (II) chloride + aluminum  aluminum chloride + copper
12.
Describe the color of your recovered copper.
13.
In a perfect experiment, your percent yield would equal 100%.
Hypothetically, what type(s) of error would result in…
a.
a percent yield of less than 100%
b.
a percent yield of greater than 100%