Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Dege on 06/11/2008 23:56:54
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hey, i am trying to melt sulfur into its pure yellow form.
but every time I try it only stays at its 3rd stage of melting,which is the almost solid stage. how can i get it to go to its complete yellow form?
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As a chemistry student I remember making brown/red 'plastic' sulphur and that if it's left to its own devices would revert over time to the yellow crystalline form. I found this too:
The S8 molecule is stable, and exists in solid, liquid and gaseous sulphur. Two crystalline forms compete, orthorhombic α-sulphur and monoclinic β-sulphur. Below 96°, the orthorhombic form is more stable, but it is a fairly narrow thing, and conversions between the two forms are slow. α-S has a density of 2.07 and melts at 113°C. β-S has a density of 1.97 and melts at 119°C. Each melts to a straw-yellow liquid of density 1.808 called λ-sulphur. If the liquid is cooled slowly, needle-like monoclinic crystals form. When the temperature falls below 96°, these crystals slowly change to orthorhombic microcrystals, which is shown by their becoming cloudy. If the liquid is heated further, at about 200°C it darkens to a reddish color and becomes viscous. The S8 rings are thermally broken, and recombine to form long chains, called μ-sulphur. The dark color is due to the free valences at the ends of the chains. If this dark sulphur is suddenly cooled by being poured into water, it becomes a rubbery mass of tangled chains. This was called amorphous sulphur, but is really a kind of glass. On standing, it eventually reverts to S8 and crystallizes. S6 molecules make rhombohedral crystals, which is called (I think) γ-sulphur. There is apparently also an S12 molecule.
Hope that helps.