The Empirical Formula of a Copper Sulfide
Lab protocol adapted by Catherine Sarisky
This lab has been scaled down to reduce the amount of sulfur dioxide emitted into the atmosphere!
Objective
To experimentally determine the chemical formula of copper sulfide.
Introduction
The empirical formula of a compound represents the lowest whole number ratio of its atoms. Sulfur, a
group 16 non-metal, commonly forms just one ion, S2- (sulfide). Copper, like many transition metals,
forms variable type cations. This means that copper can form several different ions: The copper(I) ion,
+
2+
Cu , and the copper(II) ion, Cu . As a result, we don’t immediately know what the product of the reaction
between copper metal and elemental sulfur will be
Cu (s) + S8 (s)  ??
(1)
During this reaction, you will also observe the combustion of sulfur. Any sulfur that does not react with
the copper will react with the oxygen gas in the air. An unbalanced equation for this reaction is
S8 (s) + O2 (g)  SO2 (g)
(2)
Because the product of this reaction is a gas, excess sulfur will be removed from the contents of the
crucible. Once the reaction is complete, only the copper sulfide product will remain in the crucible.
Materials
Copper filings or shot, Cu ( 0.6 g)
Sulfur, S8 (0.3 g)
Crucible and lid
Clay triangle
Ring stand
Bunsen burner
Crucible tongs
Tile
Think Safety!
 Don’t forget your lab goggles! Long hair must be tied back while flames are in use in the laboratory.
 Crucibles and lids will be hot, and will take some time to cool. You may set the hot crucible and lid
onto the tile, as it is heat-resistant. Do not set the hot crucible on your lab handout or paper towels;
the crucible will be hot enough to char paper!
 Crucibles are fragile and do not bounce well! Remove the lid from the crucible (use tongs) before
attempting to move the crucible itself using the tongs. Attempts to carry the crucible and lid together
using the tongs often result in broken crucibles and/or lids. Better yet, wait to move the crucible until
it has cooled, and then carry it in your hands.
Procedure
1. Obtain a crucible, clay triangle, and ring stand.
2. Weigh you crucible and lid.
3. Weigh out 0.6 g of copper into the crucible and record the
mass of the crucible plus copper.
4. Now add approximately 0.3 g of sulfur to the crucible. Put the
lid on the crucible.
5. Begin heating slowly, and then gradually increase the heat.
The bottom of the crucible should be in the hottest part of the
flame. Briefly lift the lid of the crucible (use tongs!) about
every five minutes to check for burning sulfur.
6. After the sulfur has stopped burning, continue to heat the
crucible to red hot for another 5 minutes. Pick up the burner
and heat the edge of the crucible lid to red hot.
7. After the crucible has cooled to room temperature, remove
the crucible lid. If you see any yellow sulfur, you’ll need to
heat the crucible and contents for a few minutes longer
before continuing. Otherwise, you can weigh the crucible
and your product.
8. Inspect the contents of the crucible. Use your observations
to answer question 2.
Questions:
1. What are the two possible products of copper and sulfur? Write the formulas for each.
2. List some physical properties of Cu (s), S8 (s), and the copper sulfide product. Has a chemical
change occurred? Why or why not?
Data Table
(show all calculations, units, and correct significant figures)
Record:
Mass of the empty crucible (before heating – NO LID)
Record:
Mass of the crucible + copper (NO LID)
Record:
Mass of the crucible and product (after heating -- NO LID)
Calculate:
Mass of the copper
Calculate:
Mass of the product
Calculate:
Mass of sulfur in the product
Calculate:
Moles of copper in the product
Calculate:
Moles of sulfur in the product
Calculate:
Ratio of moles of copper to moles of sulfur
Calculate:
Formula of the product
NOTE: For the calculated masses, make sure that the values you’re subtracting make sense.
Show work in the space in the data table or in the space below. It is much easier for you to check
your work for errors if you can review your calculations.