Ali Khan

Allotropic Forms of Sulfur

Period 5

3/17/2013

Purpose:

To observe and describe the allotropes of sulfur.

Materials:

safety goggles ring stand 50-mL beaker ring support dropper pipet wire gauze 2 watch glasses gas burner 100-mL beaker vegetable oil 250-mL beaker powdered sulfur medium test tube filter paper circles test-tube holder distilled water tweezers paper towels magnifying glass

Procedure:

Part A. Orthorhombic Sulfur1. Pour vegetable oil to a depth of about 0.5 cm into a 50-mLbeaker.2. Add a pea-sized sample of sulfur to the oil.3. Using a gas burner, heat the oil-sulfur mixture over a low flamefor a few seconds. CAUTION: Excessive heating may cause thesulfur-oil mixture to ignite, producing toxic fumes.4. Using a dropper pipet, place a few drops of the warm oil-sulfurmixture on a watch glass. Put the watch glass and beaker aside.After about 20 minutes, examine the product under amagnifying glass. Record your observationsand sketch the shapes of any crystals that have formed.

Part B. Monoclinic Sulfur5. Fold a circle of filter paper into the conical shape used forfiltering, and place it in a 100-mL beaker for support, as shownin Figure 21.1.6. Fill a medium test tube about one-third full with powdered

sulfur.7. Heat the test tube over a low flame. CAUTION: Slow heating isrecommended. Continue heating until all the sulfur has meltedto an orange-yellow liquid.8. CAUTION: Molten sulfur can cause painful burns. Pour theliquid sulfur rapidly into the filter paper cone. As soon as thesulfur begins to solidify, carefully use tweezers to remove thefilter paper from the beaker. Place the open filter paper on awatch glass. Examine the product with a magnifying glass or amicroscope. Record your observations and sketch any crystalsthat have formed.

Part C. Plastic Sulfur9. Add 150 mL of water to a 250-mL beaker. Fill the test tube usedin Part B about one-third full with sulfur.10. Heat the test tube in a burner flame until the sulfur just beginsto boil. The sulfur should be dark red at the boiling point.CAUTION: Sulfur has a boiling point of 444 C!11. Rapidly pour the hot sulfur into the beaker of cold water, asshown in Figure 21.2. When the sulfur is cool, remove it fromthe water and place it on a paper towel to dry. Examine the drysulfur, using a magnifying glass or microscope. Record yourobservations and sketch this form of the sulfur.12. Properly dispose of the materials.

Data:

DATA TABLE 1: OBSERVATIONS OF ALLOTROPIC SULFUR

Allotrope Description Drawing of sample

orthorhombic sulfur blocky crystals

monoclinic sulfur small needles

plastic sulfur amorphous

Analysis/Conclusion

1. Which allotropes of sulfur are crystalline? Compare the structure of any crystalsformed.Orthorhombic sulfur forms rectangular/blocky crystals. Monoclinic sulfur forms needlelike and sharp structures.

2. What happened to the plastic sulfur upon standing for a time? What does thissuggest about the relative stabilities of the allotropes of sulfur?

The plastic sulfur changes from having no crystalline form to having orthorhombic and monoclinic crystals embedded in the solid. This would suggest that the crystalline forms are the more stable forms of sulfur.

3. Design an experiment to determine which of the crystalline forms of sulfur is themost stable at room temperature and 1 atm pressure.

I’d store the crystalline forms under those conditions, and I’d observe any changes that happened over time.