Exp 04: Chemical Formula
Your job is to react copper wire (Cu) with sulfur powder (S8) using heat
from a bunsen burner to form a copper sulfide compound.
Then to determine and justify the molecular formula of that compound.
CuXSY
Exp 04: Chemical Formula
Procedure
1. Support a clean, dry, porcelain crucible and cover on a clay
triangle and dry by heating to a dull red in a Bunsen burner
flame. Allow the crucible and cover to cool to room
temperature and weigh them. Record the mass to the nearest
0.01 g.
2. Place 1.5 to 2.0 g of tightly wound copper wire or copper
turnings in the crucible and weigh the copper, crucible, and
lid to the nearest 0.01 g and record your results. Calculate
the mass of copper.
3. In the hood, add sufficient sulfur to cover the copper, place
the crucible with cover in place on the triangle, and heat the
crucible gently until sulfur ceases to burn ( blue flame) at the
end of the cover. Do not remove the cover while the crucible
is hot.
4. Heat the crucible to dull redness for about 5 minutes.
5. Allow the crucible to cool to room temperature. This will take
about 10 min. Then weigh with the cover in place. Record the
mass.
6. Again cover the contents of the crucible with sulfur and
repeat the heating procedure. Allow the crucible to cool and
reweigh it. Record the mass. If the last two weighings do not
agree to within 0.02 g, the chemical reaction between the
copper and sulfur is incomplete. If this is found to be the
case, add more sulfur and repeat the heating and weighing
until constant mass is obtained.
7. Calculate the mass of copper sulfide obtained. The difference
in mass between the copper sulfide and copper is the mass
of sulfur in copper sulfide. Calculate this mass. From this
information the empirical formula for copper sulfide can be
obtained, and the chemical equation for its production can
be balanced.
Exp 04: Chemical Formula
Interpreting Data (Calculations & Reasoning):
C1: Determine the mass of copper you consumed in this reaction ( +/- .01
grams).
C2: Determine the mass of copper sulfide you produced ( +/- .01 grams).
C3: Determine the mass of sulfur in your copper sulfide ( +/- .01 grams).
C4: Calculate the empirical formula for the copper sulfide you formed.
C5: Theoretically, two copper sulfides can exist. One has a molecular
weight of 159.157 amu (and therefore molar mass of 159.157 g/mol), the
second has a molecular weight of 95.611amu (and therefore molar mass
of 95.611 g/mol). Considering the empirical formula you determined
above, only one of these is the possible product of today's experiment.
Which is it and why?
C6: Assuming the two copper sulfides above are the only possible copper
sulfides, you now know the molar mass of the of the compound you
produced today. Calculate the molecular formula of the copper sulfide
using that molar mass and the empirical formula you discovered.
CuXSY
Questions?