Chemistry Lab 4 A Cycle of Chemical Reactions of Copper -...

Walsh, 1
Matthew Walsh
Section 13
November 3, 2009
A Cycle of Chemical Reactions of Copper
Introduction:
Copper is a metallic element that can undergo an easily observable set of chemical
reactions that pass copper from one chemical step to another in a cycle that both starts
and ends as elemental copper. The process of these reactions is as follows:
Cu(s)  Cu(NO
3
)
2
(aq)
 Cu(OH)
2
(aq)
 CuO(s)
 CuSO
4
(aq)
 Cu(s)
A more detailed account of these reactions is given in the “Equations” section.
Copper is easily dissolved in nitric acid and in concentrated sulfuric acid. This is
important, because these two acids are used in the above-described cycle. It is equally
important to note that there are many observable changes upon shifts between chemical
steps in the cyclical reactions outlined above. This experiment highlights macroscopic
changes in color, appearance, and bulk. As have been described, the lab’s purposes are:
to understand classifications of reactions (as demonstrated in this experiment), to learn
techniques for recording and interpreting macroscopic changes (such as those undergone
by copper), and to practice quantitative laboratory techniques (for example, synthesis,
separation, filtration, quantitative transfers) for minimalizing the loss of recovered
copper.
Experimental:
The first deviation occurred when the copper had to be covered with 4.0 mL of nitric
acid. Because the copper wire was not flattened to a full enough extent, much more than
4.0 mL was needed to submerge the copper wire. This led to using more sodium

Walsh, 2
hydroxide than was called for in the lab manual (so that the sodium hydroxide could
neutralize the nitric acid). So much sodium hydroxide was used that the solution needed
to be transferred into a larger beaker, which was another deviation from standard
procedure. The next deviation from the lab manual was that instead of using a Bunsen
burner, wire gauze, et cetera to heat the solution of Cu(OH)
2
, a hot pad was used. Also,
more Zn was added to the solution of CuSO
4
than the 2.0 g that was called for in the lab
manual. On top of the 2.06 g, which was added in small increments, 0.28 g was added to
fully react with the Cu
2+
. However, there was a period of time when another 10 mL of
H
2
SO
4
was needed to dissolve the remaining Zn, so at some point there was unreacting
solid Zn in solution with solid Cu due to a lack of acid. There were no further deviations
from standard procedure.