164 DIY Science: Illustrated Guide to Home Chemistry Experiments
POCEDURER
stoichiometrically with all of the sulfur present, the iron that is
present reacts with all of the sulfur to form a non stoichiometric
form of iron sulfide in which the proportions differ from the
stoichiometric form.mackinawite
Mackinawite has the general formula Fe(1+x)S, which indicates
that it contains a stoichiometric excess of iron and therefore a
stoichiometric deficiency of sulfur.
In this lab, we’ll prepare iron(II) sulfide using quantities of
reactants that are stoichiometrically balanced. Our product
should therefore be primarily the FeS (troilite) form of the
compound, with perhaps minor amounts of the other two
forms as contaminants. We’ll use a slight excess of sulfur,
because unless the reaction occurs under an inert atmosphere,
it’s common for the heat of the reaction to ignite the sulfur,
converting some of it to sulfur dioxide gas.
CUTIOA nS
This experiment uses the hot flame provided by a
gas burner. Be careful with the flame, and have a fire
extinguisher readily available. The reaction may be
vigorous and throw sparks that may ignite flammable
materials. The sulfur may ignite and emit toxic and choking
sulfur dioxide fumes, so perform this experiment under a
fume hood or strong exhaust fan or do it outdoors. (Even
without ignition, this reaction smells really, really bad.) The
product, iron sulfide, is pyrophoric when in powdered form,
which means that it may ignite spontaneously. Wear splash
goggles, gloves, and protective clothing.z
CUTIOA nS
Sulfur dioxide is a toxic gas with a sharp, choking
odor. You’ll certainly get a whiff of it when you do this
experiment. It will probably remind you of the smell
produced by firecrackers. If too much sulfur dioxide is
produced or the reaction becomes too vigorous, stop
the reaction by gripping the tin can lid with the tongs and
dropping the lid and reaction mixture into the pail of water.
Evacuate the area until the exhaust fan clears the air.z
1.ou have not already done so, put on your splash If y
goggles, gloves, and protective clothing.- Set up your tripod stand in the sand bed with your gas
burner set up to direct the hottest part of its flame at the
center of the ring. - Weigh the tin can lid to 0.01 g and record its mass on
line A of Table 9-1. - Center the tin can lid flat on the tripod ring.
- Weigh out 3.0 g of iron filings and 2.0 g of sulfur to
within 0.01 g and record the masses on lines B and C
of Table 9-1. - Calculate the number of moles of iron filings and sulfur,
and enter those values on lines D and E of Table 9-1. - Determine the limiting reagent from the values you
calculated in the preceding step. Assume that one mole
of iron reacts with one mole of sulfur to form one mole of
FeS, calculate the expected mass of FeS and enter that
value on line F of Table 9-1.- Combine the iron filings and sulfur in the center of a
folded sheet of ordinary paper and flex the paper back
and forth until the two chemicals are well mixed. - Pour the mixed iron and sulfur into a small pile in the
center of the can lid. Try to make the pile as compact as
possible. If the material is spread out, it’s likely that the
sulfur will catch fire and burn off to sulfur dioxide gas
before the reaction between the iron and sulfur begins.
If you are not performing this experiment outdoors, turn
on the fume hood or exhaust fan. (And you will probably
regret doing this indoors, even with an exhaust fan.)
Light the gas burner, and make sure that it’s centered
under the pile of iron and sulfur. At first, nothing appears
to happen. As you continue heating the mixture, some of
the sulfur begins to melt. Soon after, you should notice a
glow begin to develop in the mixture as the iron and sulfur
begin to react. Once that glow becomes obvious, turn
off the gas burner and allow the reaction to proceed to
completion on its own. See Figure 9-1.
Once the reaction has completed, allow several minutes
for the iron(II) sulfide and the equipment to cool.
Once the lid and iron(II) sulfide have cooled, weigh them
to 0.01 g and record the combined mass on line G of
Table 9-1. Calculate the actual mass of the product by
subtracting line A from line G and record this mass to
0.01 g on line H of Table 9-1.
Assuming that the product is pure FeS, calculate the
percent yield by dividing the actual yield (line H) by the
theoretical yield (line F) and multiplying by 100. Enter this
value on line I of Table 9-1.
Use the spatula to scrape the iron(II) sulfide into your
mortar. The product is a fused mass of lumps. Use the
pestle to crush the lumps into a coarse powder.
Use the magnet to test the iron(II) sulfide for
ferromagnetism (attraction to a magnet). If the reaction