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Plastic Sulfur

Simple Sulfur Polymer Demo

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Elemental sulfur melts from a yellow solid into a blood-red liquid. It burns with a blue flame.

Elemental sulfur melts from a yellow solid into a blood-red liquid. It burns with a blue flame. Pour molten sulfur into water to force the sulfur into polymer form.

Johannes Hemmerlein
Did you know that you can make a polymer from an element? Turn ordinary sulfur into rubbery plastic sulfur and then back into its brittle crystalline form.

Materials

  • 50 g sulfur [Compare Prices]
  • test tube (25 mm x 200 mm)
  • burner
  • test tube clamp
  • beaker of water (500 mL or so)
  • tongs

Procedure

You'll melt the sulfur, which changes from a yellow powder into a blood-red liquid. When the molten sulfur is poured into the beaker of water, it forms a rubbery mass, which remains in polymer form for a variable length of time, but eventually crystallizes into a brittle form.
  1. Fill the test tube with pure sulfur powder or pieces until it is within a couple of centimeters of the top of the tube.

  2. Using a test tube clamp to hold the tube, place the tube in a burner flame to melt the sulfur. The yellow sulfur will turn into a red liquid as it melts. The sulfur may ignite in the flame. This is fine. If ignition occurs, expect a blue flame at the mouth of the test tube.

  3. Pour the molten sulfur into a beaker of water. If the sulfur is burning, you'll get a spectacular burning stream from the tube into the water! The sulfur forms a golden-brown "string" as it hits the water.

  4. You can use tongs to remove the mass of polymer sulfur from the water and examine it. This rubbery form will last anywhere from a few minutes to several hours before reverting to the usual yellow brittle rhomic crystalline form.

How It Works

Usually sulfur occurs in orthorhomic form as eight-membered cyclic rings of monomeric S8. The rhomic form melts at 113°C. When it is heated over 160deg;C, sulfur forms high molecular weight linear polymers. The polymer form is brown and consists of polymer chains containing about a million atoms per chain. However, the polymer form is not stable at room temperature, so the chains eventually break and reform the S8 rings.

Safety

  • The sulfur is safe to recycle or dispose in any waste container.

  • Use care when handling the plastic sulfur, as it may still be hot/molten for several minutes.

  • It's best to perform this project under a hood or outdoors, since sulfur dioxide (SO2) will be released if the sulfur ignites. Sulfur dioxide is a greenhouse gas, which is irritating and toxic.

Source: B. Z. Shakhashiri, 1985, Chemical Demonstrations: A Handbook for Teachers of Chemistry, vol. 1, pp. 243-244.

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