Download Chemical Reactions of Copper and Percent Recovery

Chemical Reactions of Copper
and Percent Recovery
EXPERIMENT
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
OBJECTIVE
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
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)
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Equation 1
Chemical Reactions of Copper
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:
2H2O (l) 
 2H2 (g) + O2 (g)
Equation 2
2Mg (s) + O2 (g) 
 2MgO (s)
Equation 3
3. Combustion –

An element reacts with oxygen to form an oxide (this is also a Synthesis)

A compound consisting of carbon, hydrogen and/or oxygen (C8H18 is called
octane) reacts with oxygen to form carbon dioxide and water.
2C8H18 (l) + 25O2 (g) 
 16CO2 (g) + 18H2O (l)
Equation 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
C1A1 + C2 A2 
 C1A2 + C2 A1
Equation 5
called driving force) below is met.
a. A precipitate is formed (use solubility rules to determine when a precipitate
will form).
AgNO3 (aq) + HCl (aq) 
 AgCl (s) + HNO3 (aq)
Equation 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 H3O2 (aq) 
 HC2 H3O2 (aq) + NaCl (aq)
Experiment 9
Equation 7
9-2
Chemical Reactions of Copper
The structure below 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) 
 H2 O (l) + NaCl (aq)
Equation 7
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 8 shows a general reaction of carbonates and acids.
2HCl (aq) + Na 2CO3 (aq) 

Equation 8
CO2 (g) + H 2O (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” (i.e. we were concerned with observing “what happened”), this
lab will focus on “quantitative analysis” – an analysis based on amount rather than
observation.
Experiment 9
9-3
Chemical Reactions of Copper
This laboratory exercise will require familiarization with two separation techniques
– decantation and evaporation. The various separation techniques employed by chemists
are:
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 (Organic lab).
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
prolonged exposure to an atmosphere with which the volatile component attempts
to establish an equilibrium.
5.
Crystallization (Organic Lab). The process of providing conditions in which only
one substance in a solution will form crystals that can be collected by filtration.
Distillation (Organic Lab). 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.
6.
H2O
H2O
Place
receiving
flask in an
ice/water
bath.
Experiment 9
Sublimation. A process in which a solid
passes directly into the gas state without becoming
7.
9-4
Chemical Reactions of Copper
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 this phase,
the farther it will travel along the stationary phase.
A
B A&B
Step 1
Step 2
Step 3
Each person will be given a mass of copper wire which will be converted into a variety of
copper compounds before being returned to elemental copper.
Cu  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
Cu(NO3)2 (aq) + NaOH (aq)  Cu(OH)2 + NaNO3
Equation 10
Cu(OH)2 (s)  CuO + H2O
Equation 11
CuO (s) + HCl (aq)  CuCl2 + H2O
Equation 12
Al (s) + CuCl2 (aq)  AlCl3 + Cu
Equation 13
excess Al (s) + HCl (aq)  AlCl3 + H2
Equation 14
9-5
Chemical Reactions of Copper
Several items should be noted about Equations 9 – 14:

Some of the products are gases (i.e. NO2 and H2) – chemists love gases since they
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 15.
% Recovery =
actual mass
× 100
theoretical mass
Equation 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 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.
Experiment 9
9-6
Chemical Reactions of Copper
A: Equation 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].
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 – 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 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 11: Addition of Heat
14. Place the beaker on a wire gauze seated on a ring clamp [Figure
1]. Place a few boiling stones in the beaker and stir the solution
(constant stirring) with a glass stirring rod as you bring the
Experiment 9
Figure 1
9-7
Chemical Reactions of Copper
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 [On-Line Report Sheet Q11].
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 noncopper impurities will dissolve in the hot water. Allow the solid to sediment for 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 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 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 13] and one between the hydrochloric acid
and the aluminum metal [Equation 14].
Experiment 9
9-8
Chemical Reactions of Copper
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 water (add water to just cover the copper).
Use a stirring rod to break up the clumps of copper. Decant the water.
33. Repeat Step 32 (decant the water).
34. Repeat Step 32 (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 methanol (add
methanol to just cover the copper). 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.
36. Acetone is located at the same lab station. Rinse the copper in the evaporating dish with
acetone (add acetone to just cover the copper). Use a stirring rod to break up the clumps
of copper. Decant the acetone into your beaker and place it in the acetone waste
container before proceeding to Step 37.
Experiment 9
9-9
Chemical Reactions of Copper
37. At your lab station, place the evaporating dish on the top of
a beaker containing ½ inch of boiling water [Figure 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 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.
1/2 inch H2O
Figure 2
38. 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.
39. Use non-rubberized tongs to place your evaporating dish on the lab bench to cool.
40. When the evaporating dish is cool to the touch, WIPE THE OUTSIDE DRY WITH A
PAPER TOWEL and take it to the balance area.
41. 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].
42. 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.
43. Determine the % Recovery [On-Line Report Sheet Q25].
Waste Disposal:
Place any aqueous solutions generated in this lab in the container
labeled “Aqueous Waste”. Place the methanol and acetone rinses in waste containers
labeled “Methanol Waste” and “Acetone Waste”, respectively.
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
9-10

Laboratory 9
Lab 9
Chemical Reactions of Copper
Name:___________________
Mass:___________________
Student Data Sheet
A: Equation 9: Addition of HNO3
1. Mass of Copper Wire
g
2. Observations: Cu (s) + HNO3 (aq)
B. Equation 10: Addition of NaOH
5. Observations: Cu(NO3)2 (aq) + NaOH (aq)
C. Equation 11: Addition of Heat
9. Observations: Cu(OH)2 (s) + heat
D. Equation 12: Addition of HCl
13. Observations: CuO (s) + HCl (aq)
E. Equation 13: Addition of Aluminum
17. Observations: CuCl2 (aq) + Al (s)
AND
Al (s) + HCl (aq)
F. Isolation of Copper
24. Mass of Copper
Experiment 9
g
9-11
Name:
Laboratory 9
Instructor Data Sheet
A: Equation 9: Addition of HNO3
1. Mass of Copper Wire
g
2. Observations: Cu (s) + HNO3 (aq)
B. Equation 10: Addition of NaOH
5. Observations: Cu(NO3)2 (aq) + NaOH (aq)
C. Equation 11: Addition of Heat
9. Observations: Cu(OH)2 (s) + heat
D. Equation 12: Addition of HCl
13. Observations: CuO (s) + HCl (aq)
E. Equation 13: Addition of Aluminum
17. Observations: CuCl2 (aq) + Al (s)
AND
Al (s) + HCl (aq)
F. Isolation of Copper
24. Mass of Copper
Experiment 9
g
9-12