EXPERIMENT
Chemical Reactions of Copper
and Percent Recovery
9
Prepared by Edward L. Brown, Lee University
To take copper metal through series of chemical reactions that regenerates
elemental copper. Students will classify the various reactions, write their net
ionic equations and identify the driving force responsible for the reaction.
A
P P A R A T U S
beaker (250 mL)
Bunsen burner
graduated cylinder
boiling stones
wire gauze
glass stirring rod
ring clamp
evaporating dish
ring stand
beaker tongs
C
OBJECTIVE
APPARATUS
AND
CHEMICALS
H E M I C A L S
Copper wire in numbered test tube
Aluminum foil
concentrated Nitric Acid (HNO3)
Methanol
3.0 M NaOH
Acetone
3.0 M HCl
In this lab you will perform three of the five basic types of chemical reactions:
1. Synthesis – two elements come together to form a compound.
Cl2 (g) + 2Na (s) ⎯⎯
→ 2NaCl (s)
Equation 9.1
2. Decomposition – a compound is broken down into smaller molecules and/or
elements. In lab today, you will decompose water into its elements according to
the following chemical equation:
2H 2 O (l) ⎯⎯
→ 2H 2 (g) + O 2 (g)
Copyright 2005 Chem21 LLC. No part of this work may be reproduced, transcribed, or used
in any form by any means – graphic, electronic, or mechanical, including, but not limited to,
photocopying, recording, taping, Web distribution, or information storage or retrieval systems
– without the prior written permission of the publisher. For permission to use material from
this work, contact us at info@Chem21Labs.com. Printed in United States of America.
Equation 9.2
Chemical Reactions of Copper
3. Combustion –
™ An element reacts with oxygen to form an oxide (this is also a Synthesis)
2Mg (s) + O 2 (g) ⎯⎯
→ 2MgO (s)
™
Equation 9.3
A compound consisting of carbon, hydrogen and/or oxygen (C8H18 is called
octane) reacts with oxygen to form carbon dioxide and water.
2C8 H18 (l) + 25O 2 (g) ⎯⎯
→ 16CO 2 (g) + 18H 2O (l)
Equation 9.4
4. Metathesis – two ionic species (C1A1 and C2A2) containing a cation (C) bonded to
an anion (A) are mixed together. The cations (C1 and C2) exchange anionic
partners to form the products shown (C1A2 and C2A1) when one of the four
criteria (also called driving force) below is met.
C1A1 + C 2 A 2 ⎯⎯
→ C1A 2 + C 2 A1
Equation 9.5
a. A precipitate is formed (use solubility rules to determine when a precipitate
will form).
AgNO3 (aq) + HCl (aq) ⎯⎯
→ AgCl (s) + HNO3 (aq)
Equation 9.6
b. A weak electrolyte is formed – either C1A2 and C2A1 is a weak electrolyte.
An example of a weak electrolyte is a weak acid. Weak acids are all species
where a hydrogen atom is attached to fluorine, oxygen, or to a positive
nitrogen, excluding the seven strong acids (HCl, HBr, HI, H2SO4, HNO3,
HClO3, HClO4). The Lewis structure of the product, HC2H3O2 (acetic
acid), shows that a hydrogen is attached to an oxygen making it a weak acid.
HCl (aq) + NaC2 H 3O 2 (aq) ⎯⎯
→ HC2 H3O 2 (aq) + NaCl (aq)
Equation 9.7
The structure above is a common class of weak acids called organic acids (or
carboxylic acids). The distinguishing feature of this category of acids is the
–COOH group.
H
O
H C C
H
O H
c. A non electrolyte (water) is formed. This reaction is also called a
neutralization reaction where an acid and a base react to form a salt and water.
HCl (aq) + NaOH (aq) ⎯⎯
→ H 2 O (l) + NaCl (aq)
Experiment 9
Equation 9.7
9-2
Chemical Reactions of Copper
d. A gas is formed upon mixing two compounds and/or solutions. The gases
(and their smells) commonly formed in chemical reactions are H2S (rotten
egg), SO2 (burnt match), CO2 (odorless, doesn’t support combustion), O2
(odorless, supports combustion), H2 (odorless, explosive), and NH3
(ammonia). Equation 9.8 shows a general reaction of carbonates and acids.
2HCl (aq) + Na 2 CO3 (aq) ⎯⎯
→
Equation 9.8
CO 2 (g) + H 2 O (l) + 2NaCl (aq)
5. Oxidation / Reduction – a more active metal gives its electrons to the cation of a
less active metal. The more active metal becomes a cation and the cation of the
less active metal becomes a metal. This process of transferring electrons is called
a REDOX reaction and requires that REDuction occurs only in the presence of
Oxidation (i.e. they are coupled). Oxidation is defined as the loss of electrons and
reduction is the gain of electrons.
In total, you will perform five reactions involving copper, starting with the
oxidation of copper metal to copper ion and ending with the reduction of copper ion to
regenerate elemental copper as the final product. Unlike experiments where we analyzed
the reactions “qualitatively” (we were concerned with “observing what happened” and not
with the question of “how much” reacted), this lab will focus on analyzing the various
reactions “quantitatively” - analysis based on amount rather than observation.
This laboratory exercise will require familiarization with several separation
techniques to isolate a single pure product. The separation of the components in many
mixtures routinely encountered by chemists is based on the use of one or more of the
following techniques:
1.
Decantation. The process of separating a liquid from a denser
solid. The solid component settles to the bottom of the container
(sedimentation) leaving the less dense liquid at the top where it is
removed by pouring.
2.
Extraction. The process of separating substances by
exploiting their differing solubilities in a particular solvent. Ideally,
only one component of a mixture will dissolve in the solvent of
choice leaving the other component as a solid or an
immiscible liquid.
3.
Filtration. The process of separating a liquid from a solid by
moving the solution through a material that is porous to the liquid
but not the solid. Typically, filter paper and gravity are used to
accomplish this separation.
4.
Evaporation. The process of providing conditions in which a volatile component
(usually a liquid) is removed from a less volatile component (usually a solid) by
Experiment 9
9-3
Chemical Reactions of Copper
prolonged exposure to an atmosphere with which the volatile component attempts
to establish an equilibrium.
5.
Crystallization. The process of providing conditions in which only one substance
in a solution will form crystals that can
be collected by filtration.
6.
H2O
H2O
Place
receiving
flask in an
ice/water
bath.
Distillation.
A process in which
components of mixtures are separated
based on differing boiling points – the
lowest boiling component is collected
first followed by the more volatile
components of the mixture.
7.
Sublimation. A process in which a solid passes directly into the gas state without
becoming a liquid. All substances can accomplish this feat at some particular
temperature and pressure, however, at atmospheric pressure relatively few
substances sublime.
8.
Chromatography.
A process in which
components of a mixture are exposed to two
very different physical environments – a
stationary phase and a mobile phase. Usually,
no two components in a mixture will have the
same affinity for both phases. The extent of
separation depends on each components time in
the mobile phase – the longer a component is in
Step 1
Step 2
Step 3
this phase, the farther it will travel along the
stationary phase. In a later lab, you will use
paper as the stationary phase and water/acetone as the mobile phase to separate
cations from one another.
A
B A&B
Each person will be given a mass of copper wire which will be converted into Cu(NO3)2
→ Cu(OH)2 → CuO → CuCl2 → Cu(s). The unbalanced reactions involved are as
follows:
Experiment 9
Cu (s) + HNO3 (aq) → Cu(NO3)2 + H2O + NO2
Equation 9.9
Cu(NO3)2 (aq) + NaOH (aq) → Cu(OH)2 + NaNO3
Equation 9.10
Cu(OH)2 (s) → CuO + H2O
Equation 9.11
CuO (s) + HCl (aq) → CuCl2 + H2O
Equation 9.12
9-4
Chemical Reactions of Copper
Al (s) + CuCl2 (aq) → AlCl3 + Cu
Equation 9.13
excess Al (s) + HCl (aq) → AlCl3 + H2
Equation 9.14
Several items should be noted about Equations 9.9 – 9.14:
•
•
•
•
•
Some of the products are gases (i.e. NO2 and H2) which are the easiest products to
remove from a reaction.
Water is formed in three steps and its removal is accomplished by decantation or
evaporation.
Sedimentation and decantation techniques are only employed when the copper
compound is insoluble (s) in water – the “(s)” stands for “solid”.
When the copper compound is insoluble, all other products are water soluble
(NaNO3 and AlCl3) and are removed by allowing the copper compound to
sediment and decanting the water soluble by-products away from the copper
compound.
Any water present at the end of the reaction is removed by combining it with
methanol, then acetone, followed by evaporation.
Following this final evaporation, you will obtain elemental copper – the same material
used in the very first reaction. If you obtain the same amount that you started with, then
you will have recovered 100 percent. This percent recovery is one of the most important
laboratory calculations. This value gives chemists a quick understanding of just how well
a single reaction (or in this case, multiple reactions) has occurred. This value will be
dependent on two main factors: the degree of completion of each reaction and the ability
to isolate a single product at each step. The percent recovery is calculated using Equation
9.15.
% Recovery =
actual mass
× 100
theoretical mass
Equation 9.15
The actual mass is the mass of the pure, final product as determined by a balance in the
laboratory. The theoretical mass is the mass of the product that should be present if
every reactant molecule participated in the written reaction(s) AND if the technique(s)
used to obtain the pure, final product were successful in isolating only product molecules
without losing any in the process. In today’s lab, a rare use of Equation 9.15 occurs.
Since we are starting and ending with the same pure substance (elemental copper), the
theoretical mass is the starting mass. In most reactions, the theoretical mass is calculated
by converting the mass (in grams) of Substance A to the mass (in grams) of Substance B.
A: Equation 9.9: Addition of Concentrated HNO3
PROCEDURE
1. Obtain a clean, 250 mL, graduated beaker from your lab drawer.
2. Place your name or initials on the beaker.
3. Obtain a piece of copper wire from your instructor and determine the mass of the
copper [Data Sheet Q1].
Experiment 9
9-5
Chemical Reactions of Copper
4. Twist the copper wire into a flat, tight coil (the size of a penny) and place it in the
bottom of your beaker.
5. Place your beaker in the hood.
6. Either you or your instructor will place ~ 5 mL of concentrated nitric acid (conc HNO3
is very CAUSTIC – Avoid Contact!! Use gloves!!) in the beaker. The copper metal
will be oxidized to copper ions (~5 minutes). The noxious gas, NO2, is produced in
this reaction so the beaker must be kept inside the hood.
7. Record your observations [Data Sheet Q2]. Note the state (s, l, g, aq) of each product
you will need to know this to balance the equations online. Equations 9.9 – 9.14 give
the states of the reactants but not the products.
8. After the copper wire has disappeared, fill your beaker to the 100 mL mark with
distilled water (use the graduations on the beaker to measure the water).
9. Write a balanced net ionic equation [On-Line Report Sheet Q3] and classify the
type of reaction this represents [On-Line Report Sheet Q4].
B: Equation 9.10: Addition of NaOH
10. Use a graduated cylinder to add 30 ± 2 ml 3.0 M NaOH to the copper nitrate
solution.
11. Record your observations [Data Sheet Q5].
12. Write a balanced net ionic equation [On-Line Report Sheet Q6] and classify the
type of reaction this represents [On-Line Report Sheet Q7].
13. What is driving force (reason) for the reaction [On-Line Report Sheet Q8].
C: Equation 9.11: Addition of Heat
14. Place the beaker on a wire gauze seated on a ring clamp
[Figure 9.1]. Place a few boiling stones in the beaker and stir
the solution (constant stirring) with a glass stirring rod as
you bring the solution almost to boiling. Leave the stirring
rod in the solution to avoid losing material on your lab
bench.
15. Near the boiling point, the solution will form a brown /
black precipitate and all the blue color will disappear.
Remove the heat at this point and allow the solution to cool (5
- 10 minutes) without stirring.
16. Record your observations [Data Sheet Q9].
17. Write a balanced net ionic equation [On-Line Report Sheet
Q10] and classify the type of reaction this represents [OnLine Report Sheet Q11].
Figure 9.1
18. If some of the solid has not settled to the bottom of the beaker
during the cooling period, add an additional 2 mL 3.0 M
NaOH dropwise on top of the floating solid.
19. Decant (pour off) the clear solution with minimal loss of the precipitate. The trick is
not to pour a little and then stop; then pour a little more, then stop, etc – this will just
stir up the solid in the bottom of the beaker. The trick to decantation is to pour
slowly and constantly until the solid in the bottom of the beaker is just about to
be poured out – then, stop decanting!
20. Add 100 mL boiling water (use beaker tongs) to the precipitate in the beaker – any
non-copper impurities will dissolve in the hot water. Allow the solid to sediment for
Experiment 9
9-6
Chemical Reactions of Copper
5 minutes. Decant the water taking care to minimize loss of the copper-containing
solid. What are you removing in this step [On-Line Report Sheet Q12]?
D: Equation 9.12: Addition of HCl
21. Use a graduated cylinder to add 25-30 ml 3 M HCl to the beaker.
22. Record your observations [Data Sheet Q13].
23. Write a balanced net ionic equation [On-Line Report Sheet Q14] and classify the
type of reaction this represents [On-Line Report Sheet Q15].
24. What is driving force (reason) for the reaction [On-Line Report Sheet Q16]?
E: Equation 9.13: Addition of Aluminum
25. Place the beaker containing the CuCl2 into a larger beaker filled ¾ full with ice and
water.
26. After 5 minutes, remove this beaker from the ice bath and add ~ 0.25 g aluminum foil
to the beaker. At this point two reactions are occurring in the beaker – one between
the copper ion and aluminum metal [Equation 9.13] and one between the
hydrochloric acid and the aluminum metal [Equation 9.14].
27. This reaction will take 5 - 10 minutes. You are ready to move on to the next step
when the red precipitate of copper no longer forms on the surface of freshly added
aluminum foil and there are no shiny pieces of metal (Al) in the beaker and the
solution is no longer blue. If aluminum is still present at the end of the reaction, add
more 3.0 M HCl; if solid copper is still forming on fresh aluminum foil, add more
aluminum foil. Record your observations [Data Sheet Q17].
28. Write a balanced net ionic equation for the reaction between Al and CuCl2 [On-Line
Report Sheet Q18] and classify the type of reaction this represents [On-Line Report
Sheet Q19]. What is driving force (reason) for the reaction between Al and HCl [OnLine Report Sheet Q20]?
29. Write a balanced net ionic equation for the reaction between Al and HCl [On-Line
Report Sheet Q21] and classify the type of reaction this represents [On-Line Report
Sheet Q22]. What is driving force (reason) for the reaction between Al and HCl [OnLine Report Sheet Q23]?
F: Isolation of Copper:
30. Decant most of the liquid above the copper metal into another beaker (leave ~ 20
mL).
31. Transfer this remaining 20 mL and the solid copper to a clean, dry evaporating dish.
Decant the liquid from the evaporating dish back into the beaker to aid in transferring
all the copper. Repeat as necessary so that all the copper has been transferred to the
evaporating dish. Finally, decant the water in your evaporating dish away from the
copper metal that has settled.
32. Rinse the copper in the evaporating dish with 5 mL water. Use a stirring rod to break
up the clumps of copper. Decant the water.
33. Repeat Step 32 with another 5 ml of water (decant the water).
34. Repeat Step 32 a third time with another 5 ml of water (decant the water).
35. Take your evaporating dish and a small beaker to the lab station where the methanol is
located (DO NOT TAKE THE METHANOL OR ACETONE TO YOUR
LAB STATION!!). Rinse the copper in the evaporating dish with 5 mL methanol.
Experiment 9
9-7
Chemical Reactions of Copper
36.
37.
38.
39.
40.
41.
42.
43.
Use a stirring rod to break up the clumps of copper.
Decant the methanol into your beaker and then place
it in the methanol waste container before proceeding
to Step 36.
Acetone is located at the same lab station. Rinse the
copper in the evaporating dish with 5 mL acetone. Use a
stirring rod to break up the clumps of copper. Decant
the acetone into your beaker and place it in the
1/2 inch H2O
acetone waste container before proceeding to Step
37.
At your lab station, place the evaporating dish on the top
of a beaker containing ½ inch of boiling water [Figure
9.2]. Allow the heat of the boiling water to remove the
remaining traces of acetone and dry the copper (Take
Care Not To Allow The Flame To Come Near The
Evaporating Acetone!!!
Acetone Is Extremely
Figure 9.2
Flammable!!! If the Acetone does ignite, Do Not Panic –
the fire will not hurt your product and will go out when all the acetone has
evaporated.). You may use a glass stirring rod to break up any clumps of copper, but
make sure you don’t lose any of your product by setting your stirring rod on the
counter. Scrape your stirring rod on the side of the evaporating dish to remove any
adhering copper.
Remove the heat when the copper appears dry and no longer clumps on your stirring
rod. To test for complete evaporation of the acetone, briefly pass the flame from your
Bunsen burner over the surface of the copper in the evaporating dish – if any residual
acetone is present, it will burn briefly and then die out.
Use non-rubberized tongs to place your evaporating dish on the lab bench to cool.
When the evaporating dish is cool to the touch, WIPE THE OUTSIDE DRY WITH A
PAPER TOWEL and take it to the balance area.
Tare a piece of weighing paper (0.000 g) and quantitatively transfer the solid copper
onto the weighing paper. Record its mass [Data Sheet Q24].
Crease the weighing paper and transfer the product to a small vial. Cap the vial and
affix a label containing your name and the mass of the copper – 10 POINTS – NO
VIAL, NO POINTS.
Determine the % Recovery [On-Line Report Sheet Q25].
Waste Disposal
Any aqueous solutions generated in this lab can be flushed down the sink with plenty of
water.
Lab Report:
Once you have turned in your Instructor Data Sheet, lab attendance will
be entered and lab attendees will be permitted to access the online data / calculation
submission part of the lab report (click on Lab 9 – Chemical Reactions of Copper).
Enter your data accurately to avoid penalty. The lab program will take you in order to
each calculation. If there is an error, you will be given additional submissions (the
number and penalty to be determined by your instructor) to correct your calculation.
Experiment 9
9-8
Chemical Reactions of Copper
Post-Lab Questions:
The questions for this lab can be found at
http://www.Chem21Labs.com. Do Not Wait Until The Last Minute!!!! Computer
Problems and Internet Unavailability Happen, But Deadlines Will Not Be Extended!!
On the Internet, complete any Post Lab Questions for Laboratory 9. The computer
program will check your answer to see if it is correct. If there is an error, you will be
given additional submissions (the number and penalty to be determined by your instructor)
to correct your answer.
Late Submission:
Late submission of the lab data / calculations is permitted with
the following penalties: - 10 points for submissions up to 1 day late, - 20 points for
submissions up to 2 days late.
Experiment 9
9-9
Laboratory 9
Lab 9
Chemical Reactions of Copper
Name:___________________
Mass:___________________
Student Data Sheet
A: Equation 9.9: Addition of HNO3
1. Mass of Copper Wire
g
2. Observations: Cu (s) + HNO3 (aq)
B. Equation 9.10: Addition of NaOH
5. Observations: Cu(NO3)2 (aq) + NaOH (aq)
C. Equation 9.11: Addition of Heat
9. Observations: Cu(OH)2 (s) + heat
D. Equation 9.12: Addition of HCl
13. Observations: CuO (s) + HCl (aq)
E. Equation 9.13: Addition of Aluminum
17. Observations: CuCl2 (aq) + Al (s)
AND
Al (s) + HCl (aq)
F. Isolation of Copper
g
24. Mass of Copper
Experiment 9
9-10
Name:
Laboratory 9
Instructor Data Sheet
A: Equation 9.9: Addition of HNO3
1. Mass of Copper Wire
g
2. Observations: Cu (s) + HNO3 (aq)
B. Equation 9.10: Addition of NaOH
5. Observations: Cu(NO3)2 (aq) + NaOH (aq)
C. Equation 9.11: Addition of Heat
9. Observations: Cu(OH)2 (s) + heat
D. Equation 9.12: Addition of HCl
13. Observations: CuO (s) + HCl (aq)
E. Equation 9.13: Addition of Aluminum
17. Observations: CuCl2 (aq) + Al (s)
AND
Al (s) + HCl (aq)
F. Isolation of Copper
g
24. Mass of Copper
Experiment 9
9-11