Copper Iron Stoichiometry Lab
Owen M Jacobs
AA2
September 20 2020
Abstract:
In the Cu/Fe Stoich lab students utilized techniques such as weighing by difference,
quantitative transfer, and vacuum filtration. The purpose of this lab was to utilize these
previously stated strategies in harmony with a lab procedure to identify a limiting reagent by
experimental procedure and to calculate the percent yield of a reaction. Specifically, students
aimed to identify which of the two Fe + CuSO4 redox reactions given to us took place by
selecting how much of each reactant they would use and calculate thee percent yield of Cu for
that reaction. Using 8.0000g Cu (II) Sulfate and 2.1000g Fe, my experimental results concluded
that the reaction that produced Iron (II) Sulfate occurred, the limiting reagent was Iron, and there
was a 99.20% yield of Cu.
Introduction:
In this lab specifically, students were given 2 possible chemical reactions between
aqueous copper (II) sulfate and iron powder. The reactions are as follows:
CuSO4(aq) + Fe(s) → Cu(s) + FeSO4(aq)
3CuSO4(aq) + 2Fe(s) → 3Cu(s) + Fe2(SO4)3(aq)
(1)
(2)
To determine which of the two reactions occurred, students chose a specific amount of Iron
powder and Copper (II) Sulfate that would serve as reactants. Using the selected amount of
products students could use stoichiometry of both reactions to predict the outcomes. While in the
lab, students would have needed to ensure their mass measurements for reactants were precise,
so we utilized weighing by difference. To weigh by difference, one must place an approximated
amount of solid in a weighing bottle and mass this amount. Solid is then removed from this
bottle and placed in its respective destination. When the bottle is massed again, it will have a
lower mass, and the difference between the original and final mass of the bottle containing solid
is how much was actually used.1 If this solid needed to be transferred to a new beaker,
quantitative transfer would be utilized. Quantitative transfer is a technique that can be used to
guarantee a complete transfer of substance to a separate beaker.2 For a solid reagent, DI water
from a squirt bottle can be used to wash any excess solid into the new vessel. Another important
technique we utilized was vacuum filtration. Vacuum filtration is much faster than its alternative,
gravity filtration, due to the fact that the unwanted solution and air is forced through the filter
medium by the application of reduced pressure and solid remains in the filter.3 This is ideal as it
greatly reduces the amount of time needed to filter a considerable large amount of solid and
liquid mixture.
The Cu/Fe lab presented students a reaction in which iron replaces and reduces copper.
Outside of the laboratory, reactions like these are utilized in a wide number of fields. For
example, the field of mining, but more specifically metallurgical engineering. A technical study
by members of the college of chemical engineering at Jishou University in Hunan, China found
that using scrap iron as a reducing agent in the leeching of manganese from low grade pyrolusite
(MnO2) was extremely effective under optimum leaching conditions.4 According to the
Environmental Protection Agency ferrous metals including iron and steel are the most common
metals in common waste.5 Advances like these allow new materials to be produced while
lessening the cost in resources to produce them. The iron copper sulfate reaction is also an
example of a single replacement, or displacement, reaction. Many widely used reactions in
industry are displacement reactions. The reaction between aluminum and iron oxide (thermite)
results in a massive amount of energy released as heat, aluminum oxide, and iron. This
displacement reaction is used in incendiary bombs, the reduction of metals from their oxides, and
primarily as a heat source for the welding of iron and steel.6 The chemical reaction of thermite is
most commonly used in welding rail tracks together.
Experimental:
This lab was carried out followed according to the procedure for the Copper Iron
Stoichiometry Lab stated in the lab manual.7 In the prelab, students were instructed to select the
amounts of CuSO4 and Fe powder to be used beforehand, so I instead weighed out 2.1000g Fe
(Table 1) and 8.0000g CuSO4 (Table 1) in preparation for the lab. The CuSO4 powder was then
quantitatively transferred to a 200mL beaker rather than the 150mL beaker stated in the lab
manual.7 A total of 175mL deionized water was added to the 200mL beaker containing the
copper (II) sulfate. Aside from these examples, my experiment contained no deviations from the
procedure.
Results:
Before utilizing the glass crucible to filter the final products, its mass was
32.0753±.0002g (Table 1). After products were filtered, washed, and dried, the crucible
containing copper precipitate had a mass of 34.4455±.0002g (Table 1). With these two values it
became possible to calculate the mass of Cu produced in the reaction. This mass is
2.3702±.0004g (Table 1). Number of moles for all directly measurable reactants/products are
included in Table 2.
Table 1: Mass of CuSO4, Fe, and Filtration Crucible on the same Analytical Balance
CuSO4 (g)
Fe (g)
Crucible (g)
8.0000±.0002
2.1000±.0002
32.0753±.0002
Crucible and
Cu Precipitate
(g)
34.4455±.0002
Cu Precipitate
(g)
2.3702±.0004
Table 2: Moles CuSO4, Fe, and Cu
Substance
Number of Moles (mol)
CuSO4
.05012
Fe
.03760
Cu
.03729
In order to determine which of the reactants was limiting in the instance of each reaction
(1) and (2):
Each of the reactions were balanced and number of mols CuSO4 and Fe (Table 2) were
determined. I then created BCA tables for each reaction.
For reaction (1):
Figure 1: BCA Table for reaction (1)
CuSO4 (aq)
+
Fe (s)
→
Cu (s)
+
FeSO4 (aq)
B
.05012 mol
.03760 mol
0 mol
0 mol
C
-.03760 (-x)
-.03760 (-x) mol
+.03760 (+x) mol
+.03760 (+x)
mol
A
.01252 mol
mol
0 mol
.03760 mol
.03760 mol
Since each the coefficient of each reactant and product in reaction (1) is 1, it can simply be
assumed that the reactant with a lower number of mols will be consumed entirely. In this case
.03760 mol Fe (Table 2) will be consumed. With 1:1 mol ratios it is known this reaction will
result in the creation of .03760 mol of each product, and only .03760 mol of CuSO4 will be
consumed. (Figure 1) illustrates that CuSO4 will be in excess when the reaction finishes, and iron
will be the limiting reagent.
For reaction (2):
Figure 2: BCA Table for reaction (2)
3CuSO4(aq)
+.
2Fe(s)
→
3Cu(s)
+ Fe2(SO4)3(aq)
B
.05012 mol
.03760 mol
0 mol
0 mol
C
-.05012 (-3x)
-.03341 (-2x) mol
+.05012 (+3x) mol
+.01671 (+x)
mol
A
0 mol
mol
.00419 mol
.05012 mol
.01671 mol
Using balanced reaction (2) and the number of mols CuSO4 and Fe (Table 2), a BCA table can
be constructed to calculate theoretical yields and to determine the limiting reagent. We can
calculate which reactant will be limiting by dividing the number of moles by the respective
coefficient. This will give us our x value when the correct limiting reagent is used in the
calculation mentioned previously.
.03760 mol Fe / 2 = .01880
If .01671 is the x value, the reaction would result in a negative amount of CuSO4 when the
reaction halts, so Fe is not the limiting reagent for reaction (2).
.05012 mol CuSO4 / 3 = .01671
This calculation confirms that copper (II) sulfate is the limiting reagent for reaction (2) and
.01671 is the value that should be used for x in the BCA table.
In my lab notebook I noted that after the reaction had finished, a brilliant blue color
remained in solution. The lab manual states that this brilliant blue color is a characteristic of
aqueous copper (II) sulfate.7 The experimental yield for Cu was .03729 mol (Table 2). Using my
selected masses of CuSO4 and Fe would have theoretically produced .03760 mol Cu (Figure 1)
with CuSO4 remaining when the reaction reached completion. My percent yield Cu for reaction
(1) is 99.20%. After the reaction was complete, a blue color remained in solution, indicating
leftover (excess) CuSO4. With all of this in mind, I conclude that reaction (1) occurred
predominantly with Fe as a limiting reagent.
Discussion:
The reaction that occurred, reaction (1) or reaction (2), was determined by comparing the
experimental yield of Cu to each of the theoretical yields for reaction (1) and reaction (2). The
limiting and excess reagent calculated for each reaction also helped indicate which reaction
occurred. Using these strategies, I was able to conclude that the reaction that reaction (1)
occurred beyond reasonable doubt. I paid close attention to detail and ensured I used exactly
2.1000g Fe and 8.0000g, though the analytical balance I used had a margin of error of ±.0002.
This margin of error would not have a large enough effect on my final results to lower my
percent yield significantly at all. When a substance needed to be moved from one vessel to
another, I was certain to utilize quantitative transfer to guarantee a complete transfer.3
Quantitative transfer was utilized when transferring the iron powder to the CuSO4 solution and
when I was filtering the final solution containing FeSO4 and Cu. After ensuring all substance
from the reaction beaker made it into the crucible for filtration, I performed the washes by water
and acetone called for by the lab procedure.7 I set a 10 minute timer just after I finished the last
wash according to the procedure.7 This was crucial because if the Cu precipitate was not filtered
long enough, the sample would still contain moisture which would have added mass to my final
measurement, making my experimental yield too high. If left for too long, the sample would
have reacted with oxygen in the air to form oxides, also adding to the final mass and making my
percent yield too high. Being careful in timing was crucial in order to avoid both of these
scenarios. Lastly, when handling the crucible containing the dried Cu precipitate, I used
Kimwipes between my gloves and the glass crucible in order to prevent any contaminant that
may have been on my gloves from reaching the crucible or its contents. The root of my small
margin of error likely occurred during vacuum filtration. When I had finished filtering my final
Cu product, I could see small number of miniscule shiny orange flakes on the surface of my
filtrate. It is likely that a very small amount of my copper principate passed through the filter and
was not accounted for in my final mass. This likely made my percent yield slightly lower than it
should have.
All things considered, I believe this lab was successful. A small amount of experimental error
can be traced back to my filtration step. My percent yield for reaction (1) was 99.20%. This
along with other experimental indicators, like the blue CuSO4 remaining in solution after the
reaction completed, aided me in concluding that reaction (1) occurred.
Acknowledgments:
I used the example lab report to understand how exactly to structure the report for this lab. I also
used the Lab Report Writing Guidelines to understand the lab report in a more abstract sense.
Jake Giarranto helped me understand ACS citations because I was unable to access the ACS
Style Referencing module on compass. Tommy Cahill and I read over each other’s final lab
reports. I helped Tommy with formatting (double spaced, in text citations) and corrected a few
grammatical errors.
References:
(1)
Chesney, D. WEIGHING BY DIFFERENCE. January 16, 2008.
(2)
Bell, S. A Dictionary of Forensic Science; Oxford University Press: Oxford, England,
2012.
(3)
Filtration https://orgchemboulder.com/Technique/Procedures/Filtration/Filtration.shtml
(accessed Sep 24, 2020).
(4)
Yan, S. W.; Wen-bin; Shao-feng, X. Technical Study on Leaching Low-Grade Pyrolusite
Using Scrap Iron as Reductant. December 2012.
(5)
Epa, U. S.; OLEM. Ferrous Metals: Material-Specific Data. 2017.
(6)
The Editors of Encyclopedia Britannica. Thermite
https://www.britannica.com/science/Thermit (accessed Sep 24, 2020).
(7)
University of Illinois at Urbana-Champaign Department of Chemistry. An Introduction to
Chemical Systems in the Laboratory; 2020.
References