EMPIRICAL FORMULA
DETERMINATION
Lab # 6
Taylor Fitzgerald
March 18, 2014
CHE1020
Spring 2014
Short Form Memo-Style Lab Reports
TO: Professor Michelle Sama
FROM: Taylor Fitzgerald, CIT Student
LAB PARTNER: Joe Toomey
DATE: March 18, 2014
SUBJECT: Empirical Formula Determination
Purpose:
The purpose of this lab was to experimentally determine the empirical
formula of magnesium oxide, the compound this is formed when magnesium
metal reacts with oxygen.
Summary:
What I have learned in this lab is that the empirical formula that Joe and
I gathered from this lab is Mg0, a 1:1 ratio.
Procedures:
During this lab to start each lab group sets up a ringstand with a ring,
placing a clay triangle over the ring. There must be room under the ring for the
Bunsen burner (approximately 2-3 inches). Next, connect the Bunsen burner to
the gas outlet using rubber tubing. Once a group is given the okay by the
instructor, the Bunsen burner may be turned on. Allow the flame to be about 1
inch. Next, dry a crucible by heating it over the flame of the Bunsen burner. Do
not let the crucible glow red. Now using the tongs, remove the crucible from the
triangle on the ring to a dry area at the work bench. Now the crucible and lid
need to cool until each is at room temperature. This took my group
approximately 15 minutes. Once they are at room temperature, weigh them
both together on an analytical scale.
While the crucible and lid are cooling, each group must collect a 25 cm
piece of magnesium ribbon. Gently coil the ribbon the fit inside the crucible. My
group coiled ours around a pencil. Now that the lid and crucible should be at
room temperature, place the magnesium ribbon inside the crucible and place
the lid on it. Each group will then measure and record the weight of the
magnesium ribbon, crucible, and lid all together.
Now, using the tongs, carefully return the crucible, magnesium ribbon,
and lid back to the clay triangle above the Bunsen burner. Remove the lid but
keep it nearby for the next step. Each group will heat the crucible and
magnesium ribbon until the magnesium ribbon ignites. Be sure not to inhale or
stare directly at the ignition. When the magnesium ribbon begins burning, place
the lid back on top of the crucible using the tongs and remove the Bunsen
burner from the area.
After the ignition, glowing, and smoke have all disappeared, return the
Bunsen burner underneath the crucible and being the heating process again.
Remove the Bunsen burner and lift the lid on top of the crucible about every 2-3
minutes to check the reaction. After approximately 15 minutes or so, check to
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CHE1020
Spring 2014
see if the reaction is completed. The magnesium ribbon should have
changed to a light gray/white powder (magnesium oxide). If the ribbon material
still remains after the 15 minutes, continue using the Bunsen burner until the
magnesium ribbon is powdery.
Now turn off the Bunsen burner and let the crucible and lid cool
completely. Measure and record the combined mass of the crucible, lid, and
magnesium oxide for one last measurement. Dispose of the magnesium oxide
into the approved waste bucket provided by your chemistry professor(s). Lastly,
clean up the group’s entire bench area.
Results:
Item
Mass
Empty crucible + lid
40.98 g
Crucible, lid, and
magnesium strip before
heating
Crucible, lid, and
magnesium strip after
heating
41.37 g
41.62 g
Characteristics
(shape/color)
N/A – No magnesium
strip is involved yet
Magnesium strip is
present, shiny, silver
White/gray powder
1. What was the mass of the magnesium used?
Magnesium = 0.38 g
2. How many moles of magnesium were used?
Moles of magnesium = (0.38 g / 24.30506 g/Mol) = 0.0156346045
Moles of magnesium
3. Determine the mass of the magnesium oxide formed.
41.62 g – 40.98 g = 0.64 g
4. Determine the mass of oxygen that combined with the magnesium.
41.62 g – 41.37 g = 0.25 g
5. Calculate the number of moles of oxygen atoms that were used.
(0.25 g / 15.99943) = 0.01563 Moles
6. Calculate the ratio between moles of magnesium used and moles of
oxygen used. Express the ratio in simplest whole-number form.
0.01563 : 0.01563 = 1:1 (ratio)
0.01563 : 0.01563
7. Based on your experimental data, write the empirical formula for
magnesium oxide.
MgO
8. Calculate the percent error in your determination of the
magnesium:oxygen mole ratio, using the accepted value provided by our
professor.
0.01563 – 0.01563 x 100 = 0 %
0.01563
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CHE1020
Spring 2014
Commentary: Overall I thought Joe and I worked well on this lab
together. We had good communication throughout the whole lab: Who was
gather what, who was recording, checking time, using the tongs, lighting the
Bunsen burner, ect. Our lab took us much longer than many other groups in our
lab did. For a while, we were beginning to think that we had a dead magnesium
strip. It took our magnesium strip the 23 minutes before it had ignited. But
other than that our lab was smooth sailing.
Attachments: Note that all attachments should be clearly labeled and concise,
and should refer to related sections of the memo.
1) Raw data – required but reviewed only when necessary
2) Sample calculations – required by reviewed only when necessary
3) Notes: Any other information you think might help me understand your
results and report. Optional, but may help your grade.
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