Allotropes of Sulfur

When powdered sulfur is heated, it undergoes a series of changes in appearance and physical properties. Sulfur melts, becomes highly viscous as polymer chains form, then flows more freely at higher temperatures before eventually igniting. Quenching burning liquid sulfur in water produces a flexible, rubbery form of sulfur.

1. Place powdered sulfur in a heat-resistant container and gently heat it.
2. Observe as the yellow solid melts into a brown liquid that initially flows easily.
3. Continue heating and note how the liquid becomes increasingly viscous, indicating the formation of long-chain polymeric sulfur.
4. On further heating, the sulfur flows more freely again, but may ignite with a blue flame.
5. Carefully pour the burning sulfur into a beaker of cold water.
6. Once cooled, remove the solidified sulfur from the water. Observe that it is rubbery and flexible, distinct from crystalline sulfur.

Experiments with Sulphur - Adrian's Chemistry Laboratory:

Sulfur Spaghettio Demonstration - MrLundScience:

📄 Plastic Sulfur - Chemistry Comes Alive!: https://www.chemedx.org/JCESoft/jcesoftSubscriber/CCA/CCA2/MAIN/PLASULF/CD2R1.HTM

• Compare cooled sulfur quenched in water versus sulfur allowed to cool slowly in air (which recrystallizes and becomes brittle).
• Use different cooling methods (ice bath vs. room temperature water) to test how quickly cooling affects the polymeric structure.
• Break apart quenched sulfur samples after some time to observe how they revert back to the brittle crystalline form.

• Safety glasses and lab coat required.
• Perform in a fume hood or well-ventilated area — burning sulfur releases sulfur dioxide, an irritating gas.
• Handle hot liquids with care to avoid burns.
• Keep a fire extinguisher nearby.
• Dispose of sulfur waste according to local regulations.

• Why does molten sulfur first become viscous and then flow more freely again? (Polymer chains form and then break down at higher temperatures.)
• What is the difference between polymeric sulfur and crystalline sulfur? (Polymeric sulfur is rubbery and flexible; crystalline sulfur is brittle and yellow.)
• Why does quenched sulfur slowly revert back to the brittle form? (Polymeric sulfur is metastable and gradually reorganizes into the stable crystalline form.)
• What type of chemical change occurs when sulfur ignites? (A combustion reaction forming sulfur dioxide gas.)