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Cycle of Copper Reactions

Introduction

A renowned 19th century chemist described his first experience with chemicals in the

following way:

“While reading a textbook of chemistry I came upon the statement, "nitric acid acts

upon copper." I was getting tired of reading such absurd stuff and I was determined to

see what this meant. Copper was more less familiar to me, for copper cents were then

in use. I had seen a bottle marked nitric acid on a table in the doctor's office where I

was then "doing time." I did not know its peculiarities, but the spirit of adventure was

upon me. Having nitric acid and copper, I had only to learn what the words "act upon"

meant. The statement "nitric acid acts upon copper" would be something more than

mere words. All was still. In the interest of knowledge, I was even willing to sacrifice

one of the few copper cents then in my possession. I put one of them on the table,

opened the bottle marked nitric acid, poured some of the liquid on the copper and

prepared to make an observation. But what was this wonderful thing which I beheld?

The cent was already changed, and it was no small change either. A green-blue liquid

foamed and fumed over the cent and over the table. The air in the neighborhood of the

performance became colored dark red. A great colored cloud arose. This was

disagreeable and suffocating. How should I stop this? I tried to get rid of the

objectionable mess by picking it up and throwing it out of the window. I learned

another fact. Nitric acid not only acts upon copper, but it acts upon fingers. The pain

led to another unpremeditated experiment. I drew my fingers across my trousers and

another fact was discovered. Nitric acid acts upon trousers. Taking everything into

consideration, that was the most impressive experiment and relatively probably the most

costly experiment I have ever performed. ... It was a revelation to me. It resulted in a

desire on my part to learn more about that remarkable kind of action. Plainly, the only

way to learn about it was to see its results, to experiment, to work in a laboratory.”

from F. H. Getman, "The Life of Ira Remsen"; Journal of Chemical Education: Easton,

Pennsylvania, 1940; pp 9-10.

Chemistry is the study of chemical reactions – the rearrangement of atoms to form new

materials. The passage above describes a variety of interesting reactions, some of which you

will perform in this experiment. In this experiment you will perform a sequence of reactions of

copper that form a cycle. As you record your observations, try to interpret them in terms of

chemical equations. In particular, think about grouping them by reaction type. You will also

practice quantitative laboratory techniques by determining the percent recovery of the initial

sample of copper.

The sequence or reactions in this lab begins and ends with copper metal, so it is called a

cycle of copper reactions. Because no copper is added or removed between the initial and final

steps, and because each reaction goes to completion, you should be able to quantitatively recover

all of the copper you started with if you are careful and skillful. This diagram shows in an

abbreviated form the reactions of the copper cycle.

1 2

Cu (s) → Cu(NO3)2 (aq) → Cu(OH)2 (aq)

↑ 5 ↓ 3

4

CuSO4 (aq) ← CuO (s)

Obviously, these reactions are not balanced. They simply convey the changes that copper

undergoes during the cycle. The numbers next each reaction arrow correspond to the following

balanced reactions.

(1) 8 HNO3 (aq) + 3 Cu (s) + O2 (g) → 3 Cu(NO3)2 (aq) + 4 H2O (l) + 2 NO2 (g)

(2) Cu(NO3)2 (aq) + 2 NaOH (aq) → Cu(OH)2 (s) + 2 NaNO3 (aq)

(3) Cu(OH)2 (s) → CuO (s) + H2O (l)

(4) CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)

(5) CuSO4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)

Four types of reactions are represented here. Reaction (1) is an oxidation-reduction

(redox) reaction. This involves the transfer of electrons, in this case from copper to nitrogen.

Reaction (2) is a double-replacement precipitation reaction. Note that the nitrate and hydroxide

ions switch partners as the copper hydroxide precipitates (forms a solid). Reaction (3) is a

decomposition. The hydroxide ion breaks apart, leaving one oxygen combined with the copper.

Reaction (4) is an acid-base reaction with a single replacement. The sulfate ion switches from

the hydrogen to the copper, while the protons (hydrogen ions) combine with the oxide ion

forming water. In this example, the oxide ion is a Bronsted-Lowry base, an acceptor of protons.

The final reaction is another redox reaction in which zinc loses electrons to copper.

This experiment requires you to successfully complete the following tasks:

• Carefully follow the procedure and work safely

• Make detailed visual observations about the reactions which occur

• Record data and perform calculations

Most experiments require you to perform these tasks. They are all a part of being a

successful scientist or engineer.

Equipment, Chemicals and Supplies

2 M sulfuric acid (H2SO4) plastic weigh boat nitrile gloves

3 M sodium hydroxide (NaOH) 125 mL Erlenmeyer flask hot plate

5 M nitric acid (HNO3) 600 mL beaker metal tongs

2 M hydrochloric acid (HCl) 250 mL beaker metal scoopula

methanol 50 mL graduated cylinder glass stir rod

zinc metal (Zn) granules 10 mL graduated cylinder

wash bottle w/ deionized water copper granules (Cu)

Safety Hazards

Place your backpacks, skateboards, etc. on the counter in the back of the lab. Lab sessions are

crowded, and it is important that people don’t trip and fall when working around open flames

and chemicals.

As with many experiments, the chemicals you will work with today can be harmful if you

do not work safely. Understand what you are doing, be careful, and wear your safety

protection (goggles and lab coat at all times). You will perform this experiment in the fume

hood. It is not safe to breathe large amounts of some reactants and products and some

gases produced by these reactions.

If you accidentally spill a solution, notify the GSA immediately. The GSA will clean up the

spill. If some solution gets on your hands or nitrile gloves, wash them for a minimum of 15

minutes with soap and water after removing the gloves. While it seems like this is a long time to

wash your hands, extra washing is necessary to remove chemicals which might have soaked into

your skin.

Pay attention to the GSA and follow all his or her instructions.

Procedure

To work safely and avoid making mistakes and wasting time, read the entire procedure before

starting the experiment.

Record your observations for each question (denoted by [...] notation) on your data sheet. Do

this as you perform the experiment. You will not remember what happened later after lab when

you write your lab report’s Results section.

NOTE: THE EXPERIMENT WILL BE PERFORMED IN THE FUME HOOD.

1. Take a 600 mL beaker and fill it about three quarters (350 mL) with warm water. Use heat-

resistant gloves when pouring the warm water. Place the beaker on the hot plate IN THE

FUME HOOD. Turn on the hot plate to a setting of 3 to keep the water warm. Do not allow the

water to boil.

2. Weigh a clean 125 mL Erlenmeyer flask and record the mass on your data sheet.

3. Using a weigh boat, tare (zero out) the balance and add around 0.40 grams of copper granules.

(This is a very small amount. The tip of the scoopula should be enough.) Record the mass of the

copper granules and flask on your data sheet. Add the granules to the Erlenmeyer flask by

bending the weigh boat to avoid losing the product.

4. Measure 10 mL of 5.0 M nitric acid (HNO3) using a 10mL graduated cylinder. Please use

caution and wear nitrile gloves when pouring chemicals. If any solution spills on your

gloves, remove them, and wash your hands for a minimum of 15 minutes.

5. Add the 5.0 M nitric acid to the Erlenmeyer flask with the copper granules. Cradle the

Erlenmeyer flask on top of the water bath for about 45 seconds. If any solution spills on

yourself or the surface of the fume hood, notify the GSA immediately. Please keep the

hood’s sash down to avoid inhaling the harmful fumes. Do not open all the way up as

reactions take place. Remove the flask, swirl the solution and place it back on top of the water

bath. Keep repeating this step until all the copper has dissolved.

[1] What is in the solution when the reaction is complete? Record your observations on

the data sheet.

6. Once the copper dissolves, remove the flask from the water bath. Place the flask on the bench

in the fume hood to cool. When the solution is cool, add 15 mL of deionized water.

7. Measure 15.0 mL of 3.0M NaOH with a 50mL graduated cylinder and add it to the

Erlenmeyer flask while stirring the solution with a glass rod to precipitate Cu(OH)2.

[2] What is formed in the solution besides Cu(OH)2? Record your observations on the

data sheet.

8. Place the Erlenmeyer flask back on the hot plate (setting 6). Heat, DO NOT BOIL, the

solution. Gently stir the solution with a glass rod to prevent bumping (i.e. the formation of a

large steam bubble in a locally overheated area). Record your observations on the data sheet.

If your solution begins to boil, remove the Erlenmeyer flask using metal tongs and set it on

the counter. Turn off the hot plate.

9. Once the transformation is complete, remove the solution from the hot plate using metal tongs

and continue stirring for one minute on the bench. Then allow the solid material to settle.

10. Once settled, decant (pour off) the supernatant liquid into a 600 mL waste beaker at your

bench. Be careful; avoid losing any solid. If you need more space this can be done outside of

the hood.

See the video Decantation for assistance (http://youtu.be/Xassu5TBFDs)

11. Add about 100 mL of hot deionized water to the solid that remains in the flask. Allow the

solid to settle again and decant once more into the waste beaker. If you need more space this can

be done outside of the hood.

[3] What is removed by the washing and decantation process? Record your observations

on the data sheet.

12. Measure 15 mL of 2.0 M H2SO4 with a 50mL graduated cylinder. Pour this solution into the

flask that contains the solid while stirring.

[4] What is in the solution now? Record your observations on the data sheet.

13. Using a weigh boat, weigh 1.0 gram of zinc powder. IN THE FUME HOOD, add the zinc

metal powder to the flask containing the solid solution. Stir until the supernatant liquid is

colorless. If the zinc powder forms clumps in the solution, break the clumps apart with your

stirring rod.

[5] What happens?

[6] What is the gas produced? Record your observations on the data sheet.

14. When the evolution of gas ceases (no more bubbles), decant the supernatant liquid into the

waste beaker.

15. If you see any silvery grains of unreacted Zn mixed in with your recovered Cu, add 5 mL of

2.0 M HCl and warm, but do not boil the solution. When the evolution of gas ceases, allow the

solution to cool and decant the supernatant liquid into the waste beaker.

16. Wash the recovered Cu with about 5 mL of deionized water. Allow the solid to settle and

decant the wash water into the waste beaker. Repeat the washing and decantation at least two

more times. Dispose of all aqueous waste in your waste beaker in the container labeled A.

17. In the hood, wash the solid with about 5 mL of methanol. Allow the solid to settle and

decant the methanol. Dispose of the methanol in the waste container labeled S.

18. Place the Erlenmeyer flask on a hot plate to dry the copper metal (setting 6). Remove the hot

flask from the hot plate with metal tongs. Set it on the bench top to cool.

[7] What color is the solid material? Record your observations on the data sheet.

19. Once the Erlenmeyer flask is cool and the copper appears dry, weigh the flask with the solid.

Record the mass on your data sheet.

20. Clean up your work area. Dispose of the solid copper product in the solid waste jar. Return

borrowed equipment to the stockroom.

Perform the necessary calculations and record your data on the data sheet. Calculate the mass of

the product you recovered by subtracting the weight of the empty Erlenmeyer flask from the

weight of the flask plus the copper metal. Calculate the percentage of recovery using this

equation:

% recovered = mass of Cu recovered

mass of Cu wire  100%

A significant portion of this laboratory procedure was taken from Ken Ostrowski’s website,

www.ostrowskiness.com/sections/chemistry/HTMLLab/gclab1-06.htm. Used with permission.

DATA SHEET FOR CYCLE OF COPPER

Your name

Lab partner’s name

Lab section

DATA AND OBSERVATIONS

Table 1: Data table on mass values

Measured Mass Units (g)

Erlenmeyer flask (Step 2)

Copper granules (Step 3)

Erlenmeyer flask and dry copper (Step 19)

Mass of recovered copper

Calculations on percent of copper recovered

_______________%

Answers to questions in the procedure. They should appear in the Results section of your

report. Be detailed.

Step 5: [1] What is in the solution when the reaction is complete?

Step 7: [2] What is formed in the solution besides Cu(OH)2?

Step 11: [3] What is removed by the washing and decantation process?

Step 12: [4] What is in the solution now?

Step 13: [5] What happens? [6] What is the gas produced?

Step 18: [7] What color is the solid material?

Table 2: Observations from reactions in the copper cycle

Reaction Observations

Cu + HNO3

Cu(NO3)2 + NaOH

Cu(OH)2 + heat

CuO + H2SO4

CuSO4 + Zn

Report: A template for the report is provided on Canvas. Be sure to follow the instructions in the

template for each section of the report.

Discussion Questions

Answer the following questions in the Discussion section of your report. You should consider

these questions as you are performing your experiment. Take enough notes so that you can

answer the questions after you have finished the experiment.

1. Identify the types of reactions observed and describe when they happened in the performance

of this experiment. (10 pts.)

2. What would be the effect of using a single, solid chunk of copper metal instead of the copper

granules? What would be the effect of using powdered copper metal? Describe the factor or

factors taken in consideration to answer this question. (5pts.)

2. In step 4, you were warned not to let the solution bubble due to bumping or boiling. If the

solution did splash out of the flask due to bubbling, would this affect your final product?

Explain. (5 pts.)

3. New U.S. pennies have a copper color. Why wouldn’t this cycle of copper procedure work

with a penny instead of the copper granules? Compare the characteristics each has. (5 pts.)