Yellow sulfur is heated in a flame.
- Sulfur dioxide is toxic.
- Shields, heat resistant gloves, goggles and the classroom hood must be used for this demonstration.
Chemicals and Solutions
Roll sulfur or tech grade sulfur powder
- 500 mL erlenmeyer flask
- Extension clamp
- Meker burner and matches
- Glass funnel
- Large crystallizing
- Gloves, goggles and shields
- Samples of volcanic, orthorhombic and monclinic sulfur
- Grind roll sulfur into a find powder. Fill the flask with about 1/2 inch of the powdered sulfur.
- Attach the clamp to the flask.
- Use shields around the classroom hood to contain as much sulfur dioxide vapor as possible.
- The Meker burner should have tubing long enough such that the sulfur can be heated in the down draft.
- Heat sulfur evenly over the Meker burner. Note the changes in the color and viscosity of sulfur as temperature increases. At first the sulfur will form an orange liquid. On further heating the color becomes dark red and the liquid becomes very viscous. Upon further heating the liquid becomes less viscous. At some point colorless vapors of sulfur dioxide will be given off. Hydrogen sulfide may be ignited (with an audible pop), producing blue flames. Dim the lights and quickly pour boiling (and blue flaming) sulfur into the beaker of water (pouring it around the funnel).
- Use forceps to remove the plastic from the water and show its elasticity.
- Compare the amorphous plastic sulfur to other allotropes of sulfur such as crystalline orthorhombic or monoclinic sulfur.
Monoclinic and orthorhombic sulfur consist of crown shaped rings of eight sulfur atoms. Plastic sulfur consists of very long chains of sulfur atoms rather than rings. When sulfur is heated to about 160ºC, one of the S-S bonds in some of the rings breaks and the rings open up to give chains. The sulfur atoms at each end of the chain have only seven valence electrons. Therefore they have a strong tendency to attract an additional electron and are very reactive. An S8 chain reacts with an S8 ring causing it to open up and form a 16 atom chain. As the temperature is raised the chains become longer and more tangled and the liquid becomes increasingly viscous.