Emily Sexton
4th hr
Introduction
In the real world, it is easy to find an unknown if the physical properties are
known. When doctors are trying to figure out the reason a patient is sick, physical
symptoms, like physical properties, can be used to determine the diagnosis. In
chemistry, knowing physical properties and running simple tests can help to find
information to identify the correct formula of a substance. To find the empirical
formula for the unknown copper oxide, multiple proportions needed to be found.
Multiple proportions are the mass of two separate elements combined to make
whole number ratios. The empirical formula is the smallest whole number ratio
by dividing the number of moles of each element by the smallest molar amount.
To find percent composition, take the mass of one specific element, divide it by
the molar mass of the compound, and multiply it by one-hundred. By discovering
the percent composition of each element, an empirical formula could be
determined. If the mass of unknown copper oxide is known and the mass of
copper precipitated is measured, then the empirical formula for the unknown
copper oxide may be determined.
Materials and Methods
A 100mL beaker was obtained, cleaned, and massed. Copper oxide was then
added to the 100mL beaker and massed. A second 50mL beaker was massed and
labeled, then massed again with mossy zinc included. After a 100mL beaker was massed,
25mL of distilled water was added to it to clean the stirring rod. A graduated cylinder
was then obtained with 25mL of 3 M HCl. It was then added to copper oxide in a 100mL
beaker. The solution was stirred until solid copper oxide dissolved. Five milliliters of HCl
was added to speed up the dissolving process 5 times, and the solution turned green.
Mrs.G then dumped 6 M HCl to the solution twice. The solution was left over the
weekend to dissolve, and the spatula dissolved in the solution. Zinc was added one
piece at a time to the solution. The solution was then stirred for ten minutes with a glass
rod. To speed up the process, 2.58 grams of zinc was added to the solution. A filtration
system was then set up with a ring stand, beaker, and massed filter paper. Despite a few
small spills, the filtered material was then put in oven to dry. The next day the filter
paper and solution was massed, and the remains were then thrown away.
Results
Mass
100mL Beaker
100mL Beaker + copper oxide
Copper oxide
50.95 g
53.45 g
2.50 g
Filter Paper
Filter Paper + copper
Copper
0.54 g
2.64 g
2.1 g
2.1 g/63.55g = .033mol/.025 = 1.32 mol Cu = 1 Cu
0.4 g/16g = .025mol/.025 = 1 mol O = 1 O
1 Cu: 1 O = CuO
Conclusion
The final product of this lab was copper (II) oxide. The final empirical
formula came out to be 1.321 grams of copper to one gram of oxygen. It may not
have come out perfect because part of the solution was spilled during the
filtration process. The solution took a long time to dissolve, and when the spatula
dissolved partly into our solution it added more mass as well. Once the zinc was
added on the second day, the solution began to fizz, bubble, and produce fumes
that caused the solution to precipitate. Before the filtration, the solution wasn’t
exactly clear, but it had no hint of green so it was fine to filter. Most lab groups
got the same results, but there was a lot of confusion during the whole lab on
understanding the hypothesis. If the mass of unknown copper oxide is known and
the mass of copper precipitated is measured, then the empirical formula for the
unknown copper oxide may be determined. By determining the mass of the
solution after filtering it, the unknown copper oxide could be identified as copper
(II) oxide. By knowing certain properties of an unknown solution, the solution can
be identified. If a glass of pop is on the table, it can be identified by the physical
properties color, often smell, and taste just like an unknown solution can be
identified in chemistry.
(Mrs.G- I don’t know why the layout is so messed up on this whole lab, my tab
button was not working, so I apologize that it is kind of messed up. :]
I also could not figure out moodle for the life of me.)