Action of Heat on Sulphur

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When heated, sulphur undergoes a series of characteristic changes.

• Sulphur can melt at two different temperatures.

a) If heated rapidly, it melts at 112.8^oC.

b) But if heated slowly it will melt only at 118.6^oC.

Roll sulphur is rhombic. When heated it slowly changes to monoclinic form at 96^oC. However, if the heating is gradual monoclinic sulphur continues to melts only at 118.8^oC.

Conversely, if the heating of sulphur is very rapid, the molecules do not get a chance to get rearranged, and hence it melts at slightly lower temperature of 112.8^oC.

• Molten sulphur is a pale yellow liquid consisting of eight atom rings or spheres of sulphur (Fig.13.25). These octa-atomic molecules can easily slide on top of one another. As a result the liquid is quite mobile.

• As the temperature increases, the octa-atomic ring breaks, and forms a long chain of eight atoms (Fig.13.26). The color gradually darkens form pale yellow to amber color. As more and more molecules become long chain molecules, the chains get entangled. Hence the liquid becomes less mobile. At 160^oC, it becomes so viscous that it looks almost tar-like, and it does not flow out even if the test tube is inverted.

• When heated to above 160^oC the long chain molecules break up to form short chain molecules (Fig.13.27).

This leads to an easier movement of the molecules. As a result the liquid once again becomes mobile. The color of sulphur at this state is almost reddish brown.

• At 444^oC, sulphur begins to boil giving off light yellowish orange vapors. When the vapor are cooled, they solidify to form a Yellow powder of flowers of sulphur.