Example Lab Write-up
TITLE: Decomposing Copper Oxide
Name
Period
Date
PURPOSE: (lab notebook & lab report)
The (goal, purpose) of this (experiment, laboratory work, study) is to (identify, find) the
molecular formula of an unknown metal oxide compound by (determining, calculating, deriving) its
percent composition by mass.
BACKGROUND: (lab report)
Metals can react with oxygen to (form, produce) metal oxides; these metals are then said to be
“oxidized”, such as when iron reacts with air to (form, produce) rust. (Similarly, conversely), a metal
oxide can be heated in the absence of oxygen to (form, produce) a pure metal. In this experiment, we
will decompose an unknown copper-oxide compound to determine its percent composition of copper.
PRE-LAB ASSIGNMENT: (lab notebook)
(Complete the percent mass calculations for each of the copper oxide compounds; show your work.)
PROCEDURE: (lab notebook; you have the option to cut & paste these steps into your notebook.)
1. Weigh the test tube and record the value; sig figs are determined by the precision of the scale.
2. Obtain 3-4 g of the unknown sample and carefully place it in the bottom of the test tube.
3. Re-weigh the test tube and record the exact mass.
4. Set up the lab apparatus as in Figure 1. (Include a sketch in your lab notebook.)
5. Light the Bunsen burner and adjust the air flow to get a blue cone flame. Use this hottest part
of the flame to heat the sample in the test tube. Move the flame along the tube to make sure
any sample on the sides of the test tube is reacted.
6. Once all the copper oxide has reacted, place the Bunsen burner to the side but keep it burning
to that gas continues to flow over the sample as it cools. Let it cool completely before you reweigh.
7. Determine the mass of the test tube and product (without the stopper!) and record the value.
8. Clean up per instructions.
PROCEDURAL SUMMARY: (lab report)
Summarize the laboratory procedure in an expository paragraph, (do not write very step!) Here
is an example:
In this lab, we (measured, determined) the mass of an unknown copper oxide sample placed in a
test tube. Using a two-hole stopper with glass-tubing, the test tube was (positioned, placed, fixed)
between the gas outlet and the Bunsen burner to create a continual flow of gas over the sample. The
sample was heated in the test tube until all of the copper oxide decomposed to copper metal, as
indicated by ________________, and the final product was weighed.
SAFETY PRECAUTIONS: (lab notebook)
 Do not leave the gas on if the Bunsen burner does not ignite within 10 seconds; wait for the gas
to disperse before you attempting again.
 When heating the test tube, keep the flame away from the rubber stopper.
 Be sure everyone at the table is aware the flame is still burning while the test tube is cooling.
 Let the tube cool completely before handling.
Example Lab Write-up


Dispose of the copper metal product in the designated waste container; do not dispose in the
sink drain.
Wash hands before leaving.
OBSERVATIONS: (lab notebook, lab report)
This section includes your descriptions and experimental data, summarized in a data table. Examples for
this lab are as follows:
Mass of test tube =
Mass of test tube + unknown compound =
Mass of unknown sample =
Appearance:
The copper reaction product is a _________ color. The end of the reaction was signaled by the
sample turning _____________.
Mass of test tube + copper product =
Mass of copper product =
ANALYSIS: (lab notebook – raw calculations; lab report – calculations neatly presented in a data
summary table)
Your final percent mass results should go in this section, summarizing them in tabular form for easy
comparison to known values.
Compound
Cu2O
CuO
unknown
Name
%Mass
(from pre-lab)
(from pre-lab)
CONCLUSIONS: (lab report)
The percent mass of the copper in our unknown sample was ________%. This value (is
comparable to, is equal to) the calculated percent mass for copper (XX) oxide; therefore, the molecular
formula unknown sample is ___________, whose chemical name is _____________________.
NOTE: If the experimental results do not correspond to the percent masses for either compound,
this section should include a discussion on possible or known sources of experimental error.
SUMMARY: (lab report)
When a metal oxide is heated in the absence of oxygen the compound is decomposed and a
pure metal is produced. In this experiment, an oxygen-free environment was maintained in the
(reaction vessel, test tube) by (directing, introducing) the gas flow (through, into) the test tube before
reaching the Bunsen burner. If the test tube had been (kept open to, exposed to) the air,
______________________ (write your hypothesis with rationale….would there be a reaction??) (Lastly,
finally), we know the reaction product should weigh less than the metal oxide because it has (less, a
lower) ________.