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NO2
Cu
H2
HNO3
Al
Mg
CuSO4
Cu(NO3)2

H2SO 4
CuO
H2O
The Copper Cycle Experiment:
INTRODUCTION:
In this experiment we will explore chemical reactions of copper metal. You’ll start with
approximately 40 mg of copper and do the following chemical reactions:
1. Dissolve the copper metal and make copper (II) ion:
When nitric acid is added to copper metal, each copper atom gives 2 electrons to the 2 nitrogens in nitric
acid:
Molecular equation: Cu(s) + 4HNO3(aq)  2NO2 (g) + Cu(NO3)2 (aq) + 2H2O(l)
Ionic Equation:
Cu(s) + 4H+(aq) + 4NO3- (aq)  2NO2 (g) + Cu2+ (aq) +2NO3- (aq) + 2H2O(l)
Net ionic equation:
Cu(s) + 4H+(aq) + 4NO3- (aq)  2NO2 (g) + Cu2+ (aq) + 2NO3- (aq) + 2H2O(l)
Cu(s) + 4H+(aq) + 2NO3- (aq)  2NO2 (g) + Cu2+ (aq) + 2H2O(l
↑ blue copper (II) ion, aka cupric ion
Copper loses electrons and is oxidized to blue
copper (II) ion. Nitrogen gains the electrons copper
loses, and is reduced to reddish-brown nitrogen
dioxide gas. Nitric acid is an
Oxidation:
The loss of
oxidizing agent. This type of reaction,
electrons.
in which electrons are lost and
gained, is called an oxidationOxidizing
reduction reaction or redox reaction.
agents get
reduced.
Copper penny dissolving in concentrated HNO 3. Reddishbrown NO2 gas is being blown off.
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2. Make insoluble copper (II) hydroxide:
Copper (II) ion will react with hydroxide ion, OH-, and make insoluble copper (II) hydroxide, Cu(OH)2.
Copper (II) hydroxide looks like light blue Jello. 6 M sodium hydroxide, NaOH, is the source of
hydroxide ions. This is a metathesis, or displacement, reaction. It is not a redox reaction; no electrons
are being lost or gained. In this reaction, the cages of water around copper (II) ions are being displaced
by hydroxide ions, and cages of water around hydroxide ions are displaced by copper (II) ions.
Molecular equation: Cu(NO3)2 (aq) + 2NaOH3(aq)  Cu(OH)2(s) ↓ + 2NaNO3(aq)
Ionic equation:
Cu2+ (aq) 2NO3- (aq) + 2Na+(aq) + 2OH-(aq)  Cu(OH)2(s) ↓ + 2Na+(aq) + 2NO3-(aq)
Net Ionic Equation: Cu2+ (aq) + 2NO3- (aq) + 2Na+(aq) + 2OH-(aq)  Cu(OH)2(s) ↓ + 2Na+(aq) + 2NO3-(aq)
Cu2+ (aq+ 2OH-(aq)  Cu(OH)2(s) ↓
A note on the superscripts, subscripts, etc., in balanced equations:
(aq) ≡ aqueous, dissolved in water. Ions are dissociated. NaOH (aq) means that solid NaOH dissolved in water and broke
apart (dissociated) into sodium ions (Na+(aq) ) and hydroxide ions (OH-(aq). Each ion is hydrated, that is, surrounded by a
cage of water molecules.
(s) ≡ solid, insoluble in water. Cu(s) and Cu(OH)2(s) don’t dissolve in water, they are solid.
(g) ≡ gas
↓ ≡ indicates that a precipitate forms. Soluble ions such as Cu2+(aq) and OH-(aq) react and make an insoluble product,
Cu(OH)2(s) which settles to the bottom of the test tube.
Δ ≡ heat is used to make the reaction proceed.
3.
Dehydrate Copper (II) Hydroxide. Make Copper (II) Oxide
When Copper (II) hydroxide, Cu(OH)2, is heated, it will lose a molecule of water and form black CuO(s) copper (II)
oxide:
Δ
Molecular equation: Cu(OH)2(s)  CuO(s)↓ + H2O(g)
Ionic equation:
Δ
Cu(OH)2(s)  CuO(s)↓ + H2O(g)
Δ
Net Ionic Equation: Cu(OH)2(s)  CuO(s)↓ + H2O(g)
This, by the way, is neither a redox reaction nor a metathesis reaction. It is a decomposition reaction.
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4. Dissolve the Copper (II) Oxide and Make Copper (II) Sulfate:
Copper oxide is insoluble in water, but will dissolve nicely in sulfuric acid (H2SO4). A rather nice
colored solution of copper (II) sulfate will result:
Molecular equation: CuO (s) + H2SO4(aq)  CuSO4(aq) + H2O (l)
Ionic equation:
CuO (s) + 2H+(aq) + SO4=(aq)  Cu2+(aq) + SO4=(aq) + H2O(l)
Net Ionic Equation: CuO (s) + 2H+(aq) + SO4=(aq)  Cu2+(aq) + SO4=(aq) + H2O(l)
CuO (s) + 2H+(aq)  Cu2+(aq) + H2O(l)
This is a metathesis reaction, in which oxide ion (O=) is replaced by sulfate ion (SO4=). There is also an
acid-base reaction going on: 2H+ (an acid) + O= (a base)  H2O
5. Get the Copper Metal Back:
Copper metal can be made from copper (II) ion if a source of electrons is supplied. For example, you
can plate copper metal out of a copper (II) sulfate solution in contact with the cathode of an electrolytic
cell, and in fact we’ll do that next semester. In today’s case we will use another element as a source of
electrons. Magnesium will work nicely. Copper metal will re-form, and the solid magnesium will
dissolve and make magnesium sulfate:
Molecular equation: CuSO4(aq) + Mg(s)  Cu(s)+ MgSO4(aq)
Ionic equation:
Net Ionic Equation:
Cu2+(aq) + SO4=(aq) + Mg(s)  Cu(s) + SO4=(aq) + Mg2+(aq)
Cu2+(aq) + SO4=(aq) + Mg(s)  Cu(s) + SO4=(aq) + Mg2+(aq)
Cu2+(aq) + Mg(s)  Cu(s) + Mg2+(aq)
Aluminum metal will accomplish the same thing. Copper metal will re-form, and the solid aluminum
will dissolve and make aluminum sulfate:
Molecular equation: 3CuSO4(aq) + 2Al(s)  3Cu(s)+ Al2(SO4)3(aq)
Ionic equation:
Net Ionic Equation:
3Cu2+(aq) + 3SO4=(aq) + 2Al (s)  3Cu(s) + 3SO4=(aq) + 2Al3+(aq)
3Cu2+(aq) + 3SO4=(aq) + 2Al(s)  3Cu(s) + 3SO4=(aq) + 2Al3+(aq)
3Cu2+(aq) + 2Al (s)  3Cu(s) + 2Al3+(aq)
This is another oxidation-reduction reaction. In this case, copper (II) is gaining electrons from either
magnesium or aluminum to make copper metal. Magnesium or aluminum loses electrons; they are
oxidized.
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6. Dissolve Excess Magnesium or Aluminum:
If you added too much magnesium or aluminum metal, you can make it easy to separate from your reformed copper by adding concentrated (12 M) HCl:
Molecular equation: Mg(s) +
Ionic equation:
2HCl(aq)  H2(g) +
MgCl2(aq)
Mg (s) + 2H+(aq) + 2Cl-(aq)  H2 (g) + Mg2+(aq) + 2Cl-(aq)
Net Ionic Equation: Mg (s) + 2H+(aq) + 2Cl-(aq)  H2 (g) + Mg2+(aq) + 2Cl-(aq)
Mg (s) + 2H+(aq)  H2 (g) + Mg2+(aq)
Molecular equation: 2Al(s) +
Ionic equation:
6HCl(aq)  3H2(g) +
2AlCl3(aq)
2Al (s) + 6H+(aq) + 6Cl-(aq)  3H2 (g) + 2Al3+(aq) + 6Cl-(aq)
Net Ionic Equation: 2Al (s) + 6H+(aq) + 6Cl-(aq)  3H2 (g) + 2Al3+(aq) + 6Cl-(aq)
2Al (s) + 6H+(aq)  3H2 (g) + 2Al3+(aq)
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EXPERIMENT:
PROCEDURE:
Remember, observation is the key to science! Record all observations. Be specific. What colors did you
see? How did the colors change when you added something? What color were the copper compounds
you made? After re-reading your lab notes, you should be able to recognize nitrogen dioxide gas from
your description when you are 93! Also, this lab is not from the back of a Campbell’s Soup can. Clearly
note what YOU do experimentally. Did you need to add 27 drops of HNO3? Did you add 4 mL of 8 M
NaOH instead of 5 drops of 6 M NaOH? Record it!
Before you come to lab: In your lab notebook, at minimum have:
1. An outline of the procedures you will follow today;
2. Balanced chemical equations for every step;
3. Calculate how many grams is 40 mg.
1. Weigh about 40 mg (to the nearest 0.1 mg) of copper wire and put it into a centifuge tube. Get
another test tube and weigh out another 40 mg (to the nearest 0.1 mg) of copper wire
Perform the following steps to the contents of each test tube. You will be doing duplicate experiments
concurrently. Remember, the essence of science is to strive to reproduce your work!
REACTION 1
IN THE HOOD, add about 20 drops of concentrated (16 M) nitric acid. Keep your test tubes in the hood
until all the copper has dissolved. After the reaction is complete, add as many drops of distilled water as
you added HNO3. Remember, note your observations! Write them down in your notebook! In your notebook
lab report, write the balanced equation for the reaction taking place. Carefully describe each reactant(what color is
it? What does it look like?) and product.
CAUTION! Concentrated nitric acid is corrosive! Keep it out of your eyes! If you get any on your skin or
clothing, wash the area thoroughly with water. By the way, you will be able to tell if you get HNO 3 on your skin,
as it will react with the proteins in your skin, nitrating them and turning them yellow. Affected skin areas will stay
yellow until you shed that layer of skin cells (about a week).
CAUTION! Don’t inhale the NO2! It’s toxic!
REACTION 2
Put the test tubes in an ice bath ( a beaker full of crushed ice will do nicely). Slowly add drops of 6 M
NaOH. Add 2 or 3 drops, flick the test tubes briskly with your finger to stir the contents, and return
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the tubes briefly to the ice to chill them. Keep adding NaOH in small amounts until no further
precipitate is formed (about 20 drops). Note your observations. Write them in your notebook! Now! In your
notebook, lab report, write the balanced equation for the reaction taking place. Carefully describe each reactant and
product. What do they look like? Describe, vividly, what happened.
CAUTION! Sodium hydroxide is corrosive! If you get it on your fingers, that slippery feeling is the protein
and lipid in your skin dissolving. If you get any on your skin or clothing, wash the area thoroughly with water.
Centrifuge your test tubes for about 30 seconds. Make sure the tubes are balanced, or the centrifuge will
walk off the bench. Your instructor will show you how to balance the centrifuge. You’ll find that the
solid Cu(OH)2 has packed in the bottom of the test tube. Solids that come out of solution, like Cu(OH)2,
are called the precipitate, or ppt. The liquid on top is called the supernatant, or soup. This liquid
contains anything still in solution (aqueous). In this case, it contains sodium ion, Na+(aq) , nitrate ion,
NO3-(aq) and water.
If the supernatant is blue what additional ion does it contain? Even if the
supernatant is not blue, to make sure all the copper (II) ion has precipitated, add 5 more drops of 6 M
NaOH. Do clouds form around the drops as they hit the supernatant? There’s still copper (II) ion in
there. Add 5 MORE drops of 6 M NaOH, and centrifuge again.
When all the copper (II) ion has come down as Cu(OH)2, carefully suck off the supernatant with a
Pastuer pipet & discard it. SAVE THE Cu(OH)2! Note your observations. Write them down! Wax eloquent!
In your lab report, write the balanced equation for the reaction taking place. Carefully describe each reactant and
product. Be sure you will recognize it again.
REACTION 3
Cu(OH)2 will easily lose water when you heat it, and make CuO, copper(II) oxide. What you want in
this section is to make copper (II) oxide without blowing it out of your test tube. Fire up a Bunsen
burner and set it for a low cool flame. Hold the test tube of Cu(OH)2 in a test tube clamp, tilt it to about
45o and gently pass it back & forth through the flame.
Make sure the mouth of the test tube is not pointing at anyone! Look above you at the ceiling, and observe
the Robert W. Warren Crater Fields. The Copper (II) oxide can really blow out of the test tube if heated too fast!
Be aware of what your eyes tell you…if the contents of the test tube start to plop and perk, MOVE THE
TEST TUBE out of the flame. Be aware of what your hands are telling you…if you feel the test tube start
to vibrate, MOVE THE TEST TUBE out of the flame. Be away of what your ears are telling you. If you
hear fizzing and rumbling, MOVE THE TEST TUBE out of the flame.
When the contents of the test tube are all black CuO, go on to the next section. Note your observations.
In your lab report, write the balanced equation for the reaction taking place. Carefully describe each reactant and
product.
REACTION 4
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Add 40 drops (about 2 mL) of 6 M H2SO4 (sulfuric acid) to the solid CuO. Stir the contents of the test
tube with brisk finger flicks. When the Copper (II) oxide has all dissolved, go on to part 5.
6 M H2SO4 is “dilute”, but still corrosive.
Note your observations. In your lab report, write the balanced equation for the reaction taking place. Carefully
describe each reactant and product.
REACTION 5
Add a small piece (about 0.2 cm2, we mean teeny!) of aluminum foil to the products of Reaction 4. Add
two drops of 12 M (concentrated) HCl. Add more small pieces of aluminum foil, only if needed, until
the reaction is complete. By “complete”, we mean that all the observable copper (II) ion (What color is
copper (II) ion?) has reacted and made copper metal. (What color is copper metal? What does it do in
water?)
QUESTION TO ANSWER IN LAB: HOW WILL YOU KNOW THE REACTION IS
COMPLETE? HOW DO YOU JUDGE THIS?
12 M (concentrated) is corrosive, and produces HCl vapors which are highly irritating to eyes, nose and skin.
Note your observations. Answer the questions in the previous paragraph. In your lab report, write the balanced
equation for the reaction taking place. Carefully describe each reactant and product.
REACTION 6
In a perfect world, you will add just enough Al to react with the copper (II) ion and no more. Chances
are, though, to make sure all the copper (II) is reacted, you will have added a slight excess of aluminum.
If you see any silver aluminum floating about, after all the copper has come out of solution, add an
additional drop of concentrated HCl to your test tube.
DRY THE COPPER and WEIGH IT
Decant the liquid from reaction 6. (To decant means: pour off the liquid, leaving the solid behind.
Consult your instructor for techniques. Save the entire solid product.
Add a few mL of deionized water to wash the copper in the test tube. Flick the test tube briskly with
your finger to stir it, decant the liquid and repeat the water wash two more times.
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So that drying will occur with reasonable rapidity, now wash the copper with 3 mL of ethanol twice.
Decant the liquid after each wash.
Dry the copper in the drying oven for about 15 minutes.
Obtain the mass of the dry copper.
DISPOSE OF ALL WASTE IN THE “COPPER WASTE” CONTAINER IN THE HOOD.



 What is the THEORETICAL YIELD of copper? That is, if you started with 0.04150g
of copper wire, how many grams could you get back if every reaction went 100% to completion,
and you lost not a drop of anything?
Calculate the % copper recovered in each of your trials as (g copper recovered ) x100.
(theoretical g copper)
Was your % recovery higher than 100%? Suggest 2 reasons why.
Was your % recovery lower than 100%? Suggest 2 reasons why.
ADDITIONAL PIECE FOR LAB WRITE-UP:
Calculate:
 how many MOLES of Cu you started with,
 how many MOLES of Cu(NO3)2 you could have made from that number of moles of Cu,
 how many grams of Cu(NO3)2 you could have made from that number of moles of Cu, and,
 how many MOLES of Cu you ended up with.
WASH & RETURN ALL GLASSWARE!
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Bonus: Which US coinage has the greatest % copper?
What % is it?
What element is in greatest quantity in a US Penny?
http://www.usmint.gov/about_the_mint/
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Glassware needed, per pair of students:
10 x 75 mm test
tubes
Stirring rod
Test tube rack
Test tube clamp
Centrifuge
Analytical
balances
Weighing paper
2
1
1
2
1/bench
5
Reagents needed, per pair of students:
Copper wool
Conc HNO3
6 M NaOH
6 M H2SO4
Conc HCl
Aluminum foil
ethanol
<0.1 g
1 dropper bottle
1 dropper bottle
1 dropper bottle
1 dropper bottle
< 0.1 g
1 wash bottle