Empirical Formula of Copper (?) Oxide Lab
(Due for 100% credit anytime during the week of 1/16/12. After that, -10 pts. per day.)
Purpose: (what are we trying to determine in this lab??)
To determine _______________________________________________________________________________
by calculating the ________________________________________of the unknown compound, copper (?) oxide.
Precautions: (list as many as you can think of that actually apply to this situation)
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Materials: (list as many as you can think of that we actually use in this lab)
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2.0 g black powder compound (the copper (?) oxide)
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__________________________________________

rubber tubing with L-shaped glass tubing attached
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Procedure: (list as many steps as you can think of that we actually do in this lab)
(this drawing needs to be on your formal lab report!)
1.
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2.
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3.
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4.
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5.
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6.
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7.
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8.
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9.
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10. _________________________________________________________
11. _________________________________________________________
12. _________________________________________________________
13. _________________________________________________________
Data Table:
mass of black powder given (g)
A.
mass of test tube and black powder BEFORE heating (g)
B.
mass of test tube and new color powder AFTER heating (g)
C.
description of powder in test tube AFTER heating
D.
mass of oxygen “lost” (g)
E.
mass of copper remaining (g)
F.
% oxygen
G.
% copper
H.
empirical formula
I.
name of empirical formula
J.
2.0 g
copper (___) oxide
For the calculations:
 E=B–C
 F=A–E
 G=E÷A
 H=F÷A
 I = use G and H to calculate,
compare to ideal data
(below)
 J = use data from I to
answer
No, you do not include this
instructions box on your final
draft!!! Just the data table!
Calculations: ideal data (percent composition):
copper (I) oxide = ______________
copper (II) oxide = ______________
Cu = ___ (___________) = ____________
Cu = ___ (___________) = ____________
O = ___ (___________) = ____________
O = ___ (___________) = ____________
____________ g/mol
____________ g/mol
Cu = ____________ = __________% Cu
Cu = ____________ = __________% Cu 
O = ____________ = __________% O
O = ____________ = __________% O
Caution! Unless your experiment had EXCELLENT results, your empirical
formula may not turn out “normal.” You might end up with a strange ratio like
Cu7O4. Remember, the only ratios that can possibly exist are Cu2O and CuO!
Calculations: experimental data:
Experimental Percent Composition:
Experimental Empirical Formula:
g Cu = H.__________% Cu  H._________g Cu
2.0 g total
F._______
A.
E._______
g O = G.__________% O
A. 2.0 g total
1 mol Cu
63.55 g Cu
= _________ =
1 mol O
16.00 g O
= _________ =
 G._________g O
Note: Your empirical formula
Difference between the Experimental Percent Composition and the Ideal Percent Compositions: calculation above may not clearly
________% Cu in copper (I) oxide
– H.________% Cu experimentally
–
__________% difference
_________% Cu in copper (II) oxide
H._________% Cu experimentally
__________% difference
indicate to you what the correct
formula is. So instead, think about
which calculation here has the
smaller difference. The formula
with the smaller difference is the
formula your experimental data
is indicating.
Graphs: (construct three pie charts showing the percent compositions of the ideal and experimental data) Each slice = 10%
KEY
 = Cu
=O
Ideal copper (I) oxide
Experimental copper (?) oxide
Ideal copper (II) oxide
* = Cu2O or CuO
Conclusion: The compound that was decomposed in the test tube was ____*____, copper (___) oxide, because
the percentages calculated from the actual data more closely match the ideal percentages of this
compound (a difference of _______%) than they do the ideal percentages of the other copper oxide
compound, ___*____ (a difference of _______%).
Questions:
(Answer the following questions with full sentences, meaning, you must re-state the question in your answer. Also, number your answers in
the same way as the questions are numbered below.)
1. Write and balance the reaction that took place. (use your data to predict the product)
To access an easy-to-use
2. Briefly (but specifically) describe what change(s) you saw occurring to the
TEMPLATE for your lab,
copper oxide powder as it was heated, and tell approximately how long it took.
go to Mrs. Rigdon’s
3. Describe the color of your final product (be specific).
website,
then click on
4. Why do you think we ran the burner’s methane gas into and out of the test tube
“Important Files.” Then
during the heating process, rather than heat the compound in the open air?
click “Other Important
5. Why do we call this reaction a “decomposition” reaction—what’s decomposing?
Information.” You will find
6. Why did your instructor come around and tap on the test tube occasionally
the template for this lab at
during the heating process—what does this prevent from happening?
the bottom of the list.
7. Where does the oxygen that is separated from the copper oxide go—what
happens to it?
8. What were some possible sources of error in this lab (i.e. why didn’t you get exactly the same percentages as
you calculated for the ideal data)?
Rules for writing your lab report:
 MUST BE TYPED—hand-written reports will NOT be accepted
 double or 1.5-line spaced (no single spacing)
MOST IMPORTANT: follow the format of this handout!!!
 12 point “Times New Roman” or “Arial” or other normal font
 name, date, and period in top right-hand corner (like on a funsheet, for example)
 title: Empirical Formula of Copper (?) Oxide Lab (no separate title page, just make sure this title appears at the top of your 1st page)
 if more than one page (most likely, it will be), staple them together
 Mrs. Rigdon is looking for two main things: neatness and accuracy. Make sure your report has both!
 Due for 100% credit anytime during the week of 1/16/12. After that, -10 pts. per day. That means printed out and ready to turn in when you
walk in the door sometime that week.