Laboratory Experiment: Allotropic Forms of Sulfur
Objective
In this experiment, the different forms of sulfur will be examined after they are produced.
Special emphasis will be placed on the physical appearance of the test tube sample and the
magnified crystals. The changes observed will be physical changes, because the sulfur identity
will not change at each step.
Materials
Test Tube (1)
Test Tube Holder
Large Beaker
Sulfur
Bunsen Burner
Magnifying Glass
Filter Paper
Funnel
Introduction
Sulfur exists in several different allotropic forms depending on the surrounding conditions
(pressure, temperature) and the arrangement of groups of sulfur atoms. Sulfur is an element
well known to the ancients, and is referred to in Genesis as “brimstone”. In this lab, we will
produce monoclinic sulfur by SLOWLY melting some sulfur in a test tube and cooling it in filter
paper. The monoclinic crystals will then be examined under a magnifying glass. A 2nd test
tube will also be heated, this time to boiling, and the sulfur will be poured into a beaker of
cold water, thus producing amorphous sulfur. The amorphous sulfur will also be examined for
physical characteristics. Finally, after a few days, the monoclinic sulfur crystals and the
amorphous sulfur will be re-examined.
Pre-Lab Worksheet: Allotropic Forms of Sulfur
Please use the helpful sources (internet, dictionary, your textbook, etc.) to answer the following
questions.
1. What is an allotrope?
2. Which group on the periodic table does sulfur belong to?
3. How is sulfur naturally found?
4. What are two allotropic forms of sulfur? Please sketch each crystal structure.
5. What does the word “amorphous” mean?
6. What is a diatomic molecule?
7. What is a polyatomic molecule?
8. What are the formulas for each type of polyatomic molecule sulfur can exist as?
9. What does the word “viscous” mean?
10. Sulfur melts to form a ________ , _________ liquid, and burns with a ________ flame.
11. What is the melting point of sulfur? The boiling point?
12. What are three examples of how sulfur can exist combined with other elements?
Please list the chemical formulas for these substances.
13. How does the polyatomic molecule S8 exist? Please sketch either a ball and stick model
or a space-filling model.
Procedure
Part A
1. Fold your filter paper into a cone-shaped funnel. Lay these aside for later use.
2. Fill a test tube 1/3 full with sulfur.
3. CAREFULLY melt the sulfur by holding the tube in an inclined position about 4 inches
above a small Bunsen flame. Rotate the tube slowly as the sulfur melts. At no time
should the color of the sulfur turn dark brown!!
4. Using the funnel as a support for your filter paper, pour the melted sulfur into it. As
soon as crystals have formed from the edge to the center of the surface, and just before
it all turns solid, unfold the paper. Examine the crystals with your magnifying glass.
5. Make a drawing of the crystals in your lab notebook.
6. Observe crystals after 48 hours and record changes, if any occur. (Mark filter paper
with your name.)
Part B
1. Fill a test tube 1/3 full with sulfur.
2. Heat sulfur with the Bunsen flame until it boils. Tip the tube now and then and note
the color and consistency changes. (DO NOT BECOME ALARMED IF THE SULFUR
STARTS TO BURN). Pour the boiling sulfur into a beaker of cold water, keeping the
mouth of the tube moving in a circle.
3. When threads of sulfur have cooled (a few minutes), pour away the water. Observe
and touch the threads for texture, color, etc. Document your observations in your lab
notebook.
4. Place sulfur on a paper towel marked with your name. Observe physical
characteristics over the next 48 hours.
Data and Observations - in your lab notebook (you may take photographs)
Observations During
Melting of Sulfur
Physical Characteristics
of Sulfur Crystals
Sketch of
Monoclinic
Sulfur Crystals
Observations of
Crystals in 48
hours
Observations During
Boiling of Sulfur
Physical Characteristics
of Amorphous Sulfur
Sketch of
Amorphous
Sulfur
Observations of
Amorphous sulfur
in 48 hours
Part A
Part B
Clean-up Procedures
1. After the test tubes have cooled, return them to the central location where you
received them. Since the sulfur is insoluble in water, the test tubes will not come clean,
and will be used again for this lab in future classes.
2. Label your samples and place them at the back of the room for future observations.
3. Clean and dry all of your equipment and return it to your drawer. You can use the
soapy squirt bottle solution under the sink for cleaning equipment.
4. Using damp paper towel, wipe the lab benches down to remove any traces of sulfur
powder. Discard this in the trash can.
5. Using a damp cloth, wipe the lab benches down a second time.
6. (Last hour of the day) When the Bunsen burners are cool, please return them to the
appropriate location. Please put the strikers away too.
7. Place the soapy solution back under the sink.
8. Double-check your work area for cleanliness.
9. Wash your hands with soap and water.
Conclusions and Questions
You have observed six different forms of sulfur in this activity. First, the powdered sulfur
you began with was the orthorhombic allotrope. After being heated carefully, the sulfur
melted to pale yellow λ-sulfur (lambda-sulfur). This liquid solidified and formed monoclinic
sulfur crystals. When a second sample of sulfur was heated more strongly, sulfur vapor was
emitted, and a more viscous blackish liquid formed, which is called μ-sulfur (Mu-sulfur). When
the μ-sulfur was poured into the cool water, amorphous sulfur was observed. After several
days, the amorphous allotrope will turn brittle and return to the orthorhombic form.
Each form of sulfur has a different molecular structure. The following table summarizes the
various allotropic forms of sulfur.
Allotropic Forms of Sulfur
Form
Orthorhombic Monoclinic
Amorphous Lambda Mu
Vapor
Formula
Structure
S8
Rings
Varies
Chains and
rings
Tangled
robe
Solid-liquid
S2
molecules
S8
Rings
Appearance Rhombus
Needles
Phase
Solid
Solid
S8
Rings
Sn
Chains
Thin,
yellow
Liquid
Thick, red- yellow
black
Liquid
gas
Questions
1. Compare and contrast each liquid form of sulfur from each part of this experiment.
2. When the liquid Mu-sulfur forms during Part B of this experiment, the structure
changes from a ring structure to a chain structure. Knowing this information, can you
speculate why the liquid became more viscous compared to the pale yellow liquid
from Part A?
3. Why does the color change during heating?
4. Describe the process by which you produced monoclinic sulfur. What properties
differentiate it from other allotropic forms of sulfur?
5. Describe the process by which you produced amorphous sulfur. What properties
differentiate it from other allotropic forms of sulfur?
6. When sulfur is produced in large quantities for industry, it is often stored in large piles
outside. This used to be done with large piles of road salt, but this practice caused
considerable environmental damage and is no longer done. Explain why it is still
feasible to store sulfur in this manner.
7. Research and list 4 uses of sulfur.