Name: ____________________________
Per: _______
Date: _______________
Leftover Aluminum Wire
Stoichiometry – Lab #2
Pre-Lab Preparation and Questions
*Read the Introduction and Background sheet you are provided on the last page, then
answer the following pre-lab questions.*
1. Review: Balance this equation in the space below.
___ CuCl2 (aq) + ___ Al (s) ___ Cu (s) + ___ AlCl3 (aq)
2. Review: What type of reaction is this? How do you know?
3. Review: What are your reactants going to be in the lab? Your products?
4. Review: what does “yields” mean in terms of a chemical equation?
5. What is a limiting reactant?
6. In the example provided (2H2 + O2  2H2O), 10 grams of both hydrogen and
oxygen are reacted to form water. Based on the calculations they provided,
which is the limiting reactant? Explain your answer in detail.
7. What is theoretical yield? What is the equation we use to solve for this?
Name: ____________________________
Per: _______
Date: _______________
8. What is actual yield? Why do we measure this?
9. What is percent yield? What is the equation we use to solve for this?
10. What is percent error? What is the equation we use to solve for this?
11. From previous labs, what do we know about the COLOR of copper solutions?
What would happen if copper got “kicked out” of the solution?
12. What are some potential sources of error that may happen in an experiment?
13. What do you think it means for something to be “oxidized?” For example,
“copper will slightly oxidize” from procedure step #10.
Materials
*See background and intro page you were given*
Safety
*See background and intro page you were given*
Name: ____________________________
Per: _______
Date: _______________
Procedure
1. Label your test tube and your paper cups (using tape) with a group member’s
name, your class period and trial number (1 and 2).
2. Obtain about 0.5 grams of copper (II) chloride, CuCl2 crystals and put in a test
tube. Add 10 mL of distilled water and stir to dissolve the crystals.
3. Cut a 15 cm piece of aluminum wire with wire cutters. Use a small piece of
steel wool to shine the wire and to remove any impurities on the surface.
4. Measure and record the exact mass of the aluminum wire to the nearest
hundredth of a gram in the data table.
5. Use the tweezers to lower the aluminum wire into the test tube containing the
copper (II) chloride solution, CuCl2•2H2O. The wire may extend beyond the
height of the tube, this is okay.
6. Place the test tube into the boiling water bath for approximately 5-10 minutes.
The reaction is complete when the solution becomes colorless.
7. Use tweezers to remove the wire from the test tube. Use caution so as not to
disturb the copper on the wire.
8. Measure the mass of your clean, dry paper cup and record the mass in the
data table.
9. Use a spatula to scrape as much solid copper as possible from the aluminum
wire into the evaporating dish.
10. Allow the copper to dry overnight. (Note: the copper will slightly oxidize and
change color to green or dark brown. Overheating will cause the copper to
oxidize even faster.)
11. Once dry (next class period), measure the mass of the copper and the paper
cup. Record this mass in the data table.
12. Rinse the aluminum wire with tap water to remove any impurities and dry the
wire with a paper towel.
Name: ____________________________
Per: _______
Date: _______________
13. Once dry, measure and record the actual “leftover” mass of the aluminum
wire in the data table.
14. Repeat this experiment to obtain data for trial 2 using the other end of the
aluminum wire. Record all trial II data in the data table.
Data Table
Trial 1
Trial 2
Trial 1
Trial 2
Initial Mass of CuCl2•2H2O (g)
Initial Mass of Aluminum wire (g)
Mass of “leftover” aluminum wire (g)
Actual mass of aluminum reacted (g)
Mass of paper cup + copper (g)
Mass of paper cup (g)
Actual mass of recovered dry copper
Results Table
Moles of CuCl2•2H2O
Moles of Aluminum that should react
(theoretical)
Mass of aluminum (g) that should
react (theoretical)
Percent error for reacted aluminum
Predicted mass of recovered copper
(theoretical)
Percent error for recovered copper
Percent yield of recovered copper
Name: ____________________________
Per: _______
Date: _______________
Post Lab Analysis Questions
1. Write the balanced equation for the reaction that occurred between the
aluminum wire and the copper (II) chloride solution. (check pre-lab questions
for help!)
2. Which starting material of the reaction is the limiting reactant and which
material is present in excess? Show calculations and all work for your
determination of this.
3. Complete the Data Table and Results Table. Show all calculations on the page
provided (back of the packet), clearly indicating where each result came from
for each box a-g.
4. What physical evidence do you have that shows that copper (II) chloride is,
indeed, the limiting reactant?
5. Discuss reasonable and potential sources of error in this experiment.
Name: ____________________________
Per: _______
Date: _______________
6. Discuss potential reasons why the percent yield of recovered copper may be
greater than 100%.
7. Why do you think scientists add excess of one or more chemicals when
performing a reaction, rather than combine the exact stoichiometric ratio?
8. What factors do you think may lead scientists (in industry, for instance) to
decide to use a certain starting material as the limiting reactant and another as
the excess chemical?
Name: ____________________________
Per: _______
Calculations Page – Data Table (for Trials 1 & 2)
a.
b.
c.
d.
e.
f.
g.
Date: _______________
Name: ____________________________
Per: _______
Calculations Page – Results Table (for Trials 1 & 2)
a.
b.
c.
d.
e.
f.
g.
Date: _______________
Name: ____________________________
Per: _______
Date: _______________
DUE DATE FOR STOICHIOMETRY FORMAL LAB: Friday, March 22nd
TO SUBMIT: Email by Friday at 10 AM or hand in as you come to class. Email is
preferred (easier to edit/make revisions).
What about the calculations? Do we have to type them?
-
NO! Just scan in your work; that will be fine.
Please make sure it is legible.
Lab Report Requirements
Use this lab packet to guide you; all of the answers should be here if you
completed the lab and questions!
The final, typed lab report should have the following sections:
-
Purpose
o You will write your own this time
-
Introduction/Background
o use pre-lab questions to guide you
-
Materials
o Provided for you
-
Safety Precautions
o Provided for you
-
Procedure
o Provided for you
-
Data Table with calculations
o Use lab template
-
Results Table with calculations
o Use lab template
-
Discussion /Conclusion
o Use analysis/post-lab questions to guide your discussion
o Should be AT LEAST 3 paragraphs
o INCLUDE PICTURES (at least 2) in this section of the before/after results
Name: ____________________________
Per: _______
Date: _______________
STUDENT DIRECTIONS FOR TODAY’S LAB
-
Today, you will be working with your groups to complete all questions and
the lab.
-
I will answer questions as needed, but I will be pushing you to think a lot on
your own and coming up with the answers as a group.
STEPS TO TAKE
1. Read over the Intro/Background sheet on your own. Highlight/annotate as
necessary. Perhaps read the pre-lab questions first so you know what to look
for!
2. Discuss each paragraph with your group. Point out the main ideas/terms you
found and why they are important.
3. Answer the pre-lab questions as a group. Everyone must be finished before
you move on.
4. Read over the procedure and highlight the ACTIONS you must take.
5. Gather the materials/supplies needed. Double check that you have them all.
6. Begin the experiment, following the procedure carefully, step-by-step.
7. Complete any calculations you can for today, and note which ones you will
have to do during next class period.
8. Answer any analysis/post-lab questions that you can today.