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11.
2.
1 Elemental Sulfur
There are many allotropes of elemental sulfur, among which the two more common types are orthorhombic sulfur (rhombic sulfur, rhombohedral sulfur) and monoclinic sulfur
.
Orthogonal sulfur is a designated element,
△ f H m Θ =0, △ f G m Θ =0
.
When orthorhombic sulfur is heated to the phase transition temperature (368.
6K), it can be transformed into monoclinic sulfur without melting
.
When the temperature is lower than the phase transition temperature, monoclinic sulfur can be slowly transformed into orthorhombic sulfur
The molecular formula of elemental sulfur is S 8 and has a cyclic structure (Figure 11-4), in which each S atom adopts sp3 unequal hybridization
.
After the elemental sulfur solid is heated and melted and before gasification, S 8 opens the ring to form a long chain, and then rapidly cools to obtain elastic sulfur with a long chain structure and stretchability
.
Orthogonal sulfur and monoclinic sulfur with cyclic structure are easily soluble in non-polar organic solvents, such as CS 2 , C 6 H 6, etc.
, while elastic sulfur with long-chain structure is insoluble in non-polar organic solvents
Figure 1-4 S 8 cyclic molecular structure of elemental sulfur
Elemental sulfur is more active in nature.
It can react with almost all metals to form metal sulfides when heated or at high temperatures, and can also be combined with most non-metals
Using sulfur and mercury to generate HgS can remove a small amount of elemental mercury scattered on the ground in the laboratory
.
Sulfur can be oxidized by nitric acid
S+2HNO 3 =H 2 SO 4 +2NO
Under heating conditions, sulfur disproportionates in alkali
3S+6NaOH=2Na 2 S+Na 2 SO 3 +3H 2 O
11.
2.
Hydrogen sulfide H 2 S is a colorless and toxic gas with the smell of rotten eggs.
A large amount of inhalation can cause people to coma or die
.
The solubility of H 2 S in water is relatively small, and the saturation concentration is about 0.
Sulfur vapor and hydrogen gas may be directly combine to form H 2 S
.
In the laboratory, H 2 S is prepared by the action of metal sulfide and non-oxidizing acid
FeS+H 2 SO 4 (lean)=H 2 S+FeSO 4
The aqueous solution of H 2 S is called hydrosulfuric acid, which is a weak dibasic acid
.
The chemical properties of H 2 S are mainly reducing
.
It can be known from the standard electrode potential that H 2 S has strong reducibility no matter in acidic or alkaline solution
.
In the following reaction, H 2 S exhibits reducibility
