C.11 Investigating Matter: Retrieving Copper

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Name: _____________________________ Student ID Number: __________________ Period: ______
Date: ______________________
Unit 2
C.11 Investigating Matter: Retrieving Copper
Introduction
While completing Investigating Matter B.3 (pages 139–140), you heated metallic copper, producing a
black powder, copper(II) oxide (CuO). Because atoms are always conserved in chemical reactions, the
original copper atoms must still exist. In this investigation, you will attempt to recover those atoms of
metallic copper.
Before starting, read the procedure to learn what you will need to do, note safety precautions, and plan
necessary data collecting and observations. Prepare a table in your lab notebook where you can record the
various masses measured in this investigation, and clearly label what those data represent.
Procedure
Part I: Separating Copper(II) Oxide (CuO) from the Sample
Most likely, during Investigating Matter B.3, not all the original copper powder reacted with oxygen gas
when you heated the copper in air. Some copper metal probably is still mixed in with the black copper(II)
oxide. The first steps in this activity involve separating this mixture into copper and copper(II) oxide. To
do this, you will add dilute hydrochloric acid (HCl) to the black powder. Copper metal does not react with
hydrochloric acid, so it will remain as a solid. The black copper(II) oxide, however, reacts with
hydrochloric acid to produce copper(II) chloride (CuCl2) and water, as shown in the following equation:
CuO(s)
Copper(II) oxide
+
2 HCl(aq) →
CuCl2(aq)
Hydrochloric acid
Copper(II) chloride
+
H2O(l)
Water
1. Obtain your beaker containing the black powder from Investigating Matter B.3. Look closely at its
contents. Is the material uniform throughout? If not, why not?
2. Construct a data table appropriate for recording the data you will collect in this investigation.
3. Add 50 mL of 1 M HCl to the beaker containing the copper oxide mixture. Record your observations
of the solution. (Caution: 1 M hydrochloric acid may damage your skin. If some HCl does spill on
your skin, ask another student to notify your teacher immediately. Begin rinsing the affected area
with tap water immediately.)
4. Gently heat the mixture to about 40 °C on a hot plate, and maintain at that temperature for 15
minutes, stirring every few minutes with a glass rod.
5. Remove the beaker from the hot plate. Turn off the hot plate. Allow any unreacted copper metal still
remaining to settle to the bottom of the beaker. Then slowly decant the liquid into a second, empty
100-mL beaker.
6. Wash the solid copper remaining in the first beaker several times by swirling it gently with
approximately 10 mL of distilled water. Slowly decant the liquid into the second beaker, adding it to
the liquid you collected in Step 5. Set aside the collected liquid contained in the second beaker
(approximately 60 mL) for Step 9.
7. Measure and record the mass of a piece of filter paper. Transfer the solid copper to the paper, as
shown in Figure 2.35 (page 170 of your textbook), and allow it to dry overnight.
8. After the sample and filter paper have dried, find the mass of the solid copper. This represents the
portion of the original copper powder that failed to react to form CuO. Record this mass in your
laboratory notebook.
104
Name: _____________________________ Student ID Number: __________________ Period: ______
Date: ______________________
Part II: Converting Copper(II) Chloride (CuCl2) to Copper (Cu)
The final step in this investigation is to convert the dissolved copper(II) chloride (CuCl2) to copper metal.
Perhaps you already have an idea how to do this. Recall the metal activity series that you devised during
Investigating Matter B.5 (pages 142–143 of your text). By adding solid metal samples to solutions that
contain other metal ions, you compared the chemical activity of each metal. Review your observations
from that earlier investigation. Which of the tested metals are more active than copper? Try to predict the
result of placing one of those more active metals in your copper(II) chloride solution. Check your
prediction by completing these steps.
9. Obtain a watch glass that can completely cover the top of the beaker containing copper(II) chloride
(CuCl2) solution from Step 6. For each gram of copper powder that you started with from
Investigating Matter B.3, add about one gram of zinc metal to the CuCl2 solution. See Figure 2.36
(page 170 of your textbook).
10. Immediately cover the beaker with the watch glass, and allow it to stand for several minutes. Record
your observations.
11. After the reaction has subsided, remove the watch glass and gently dislodge the solid copper that has
formed on the surfaces of the zinc pieces.
12. Continue to dislodge the copper from the zinc until you are convinced that the zinc has stopped
reacting with the solution. (How can you decide?) Then, add 10 mL of 1 M HCl to the beaker and
carefully remove any large pieces of solid zinc from the beaker with forceps. Follow your teacher’s
instructions for discarding the solid zinc. Replace the watch glass. Record your observations.
13. After a few minutes, carefully decant as much of the liquid as possible into another empty beaker.
Follow your teacher’s instructions for discarding the liquid.
14. Wash the solid copper several times with distilled water.
15. Transfer the copper to a preweighed piece of filter paper, and allow the copper to dry overnight.
16. After the sample and filter paper have dried, find the mass of copper metal. This represents the copper
that you recovered from the copper(II) chloride solution.
17. Follow your teacher’s instructions for disposing of waste materials.
18. Wash your hands thoroughly before leaving the laboratory.
Questions
1. During Investigating Matter B.3, not all of the original copper powder reacted when you heated it in
air.
a. What observational evidence leads you to think that the reaction was incomplete?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
b. How would you revise the procedure so that more copper(II) oxide could form?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
105
Name: _____________________________ Student ID Number: __________________ Period: ______
Date: ______________________
2. During Investigating Matter B.3,
a. What mass of the original powdered copper sample reacted when you heated it? (Hint: Refer to
the original mass of copper you used during this investigation and the mass of copper residue
found in Step 8 to calculate this.)
______________________________________________________________________________
b. What percent of the total copper sample reacted?
______________________________________________________________________________
3. In the reaction between copper(II) chloride (CuCl2) solution and zinc metal, in Investigating Matter
B.5, each Cu2+ ion gained two electrons to form an atom of copper metal. Each zinc metal atom lost
two electrons to form a Zn2+ ion:
a. Write a balanced chemical equation that represents this process. (Hint: To review how, turn to
pages 157–161.)
______________________________________________________________________________
b. Based on the chemical equation you wrote in Question 3a, identify
i.
the reactant that was oxidized. _________________________________________________
ii.
the reactant that was reduced. __________________________________________________
iii.
the reducing agent. ___________________________________________________________
iv.
the oxidizing agent. ___________________________________________________________
4. Adding HCl to CuO, in Investigating Matter B.3, resulted in the formation of a blue solution. This
color is due to the presence of Cu2+(aq) ions. Consult your observations when answering the
following questions:
a. Describe what happened to the solution color after you added zinc (see Steps 9 and 10).
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
b. What caused the changes you observed in the solution?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
c. How can the color of the solution be used to indicate when the zinc metal has removed the Cu2+
ions from the solution?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
106
Name: _____________________________ Student ID Number: __________________ Period: ______
Date: ______________________
5. To recover Cu metal from the CuCl2 solution, you had to use other resources:
a. What resources were “used up” in this recovery process?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
b. Where (to what location) did each resource finally go?
______________________________________________________________________________
______________________________________________________________________________
107
Name: _____________________________ Student ID Number: __________________ Period: ______
Date: ______________________
Unit 2
C.11 Investigating Matter: Retrieving Copper
Data Tables
Part I
Data
Mass of filter paper
Mass(g)
Mass of filter paper and copper residue
Mass of copper residue
Part II
Observation of Beaker
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Data
Mass of filter paper
Mass(g)
Mass of filter paper and copper residue
Mass of copper residue
108
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