Oxygen compounds of hexavalent sulfur

1.
Sulfur trioxide

Sulfur trioxide SO ₃ is liquid at room temperature, with a melting point of 16.
6°C and a boiling point of 44.
6°C
.

The gaseous SO ₃ is a single molecule with a planar triangular structure.
The central S atom adopts sp² hybridization to form 3 σ bonds with 3 O atoms, and one of the molecules is delocalized without bonding
.

Liquid SO ₃ has two structures, single molecule (planar triangle) and cyclic trimer (SO ₃ ) ₃ , as shown in Figure 11-7(a); solid SO ₃ has cyclic trimer and Chain (SO ₃ )n, as shown in Figure, 11-7(b)
.

In the cyclic and chain structures, the center S adopts sp ³ hybridization, and there are two kinds of O atoms (terminal oxygen and bridging oxygen) in different chemical environments in the molecule

Figure 11-7 The trimerization and chain structure of SO ₃

2.
Sulfuric acid and its derivatives

Sulfuric acid H ₂ SO ₄ , colorless oily liquid, strong intermolecular hydrogen bond, high boiling point (337℃)
.

H ₂ SO ₄ can form a strong hydrogen bond with water molecules, so it has strong water absorption (can be used as a desiccant) and dehydration

The H ₂ SO ₄ molecule has a tetrahedral structure (Figure 11-8)
.

The central S atom adopts sp ³ unequal hybridization, the single electron in the hybrid orbital forms a σ bond with the oxygen in -OH, and the electron in the S atom hybrid orbital faces the end O atom

Figure 11-8 Schematic diagram of the molecular structure of H ₂ SO ₄

Sulfuric acid is a strong dibasic acid, the first stage is completely dissociated, and the second stage dissociation constant K ^Θ a ² =1.
0×10 ^-2
.

Concentrated sulfuric acid mainly exists in a molecular state.
The strong polarization of H ⁺ causes the SO bond to be easily broken and has a strong oxidizing property.
It can oxidize many metals and non-metal elements, and can also oxidize KI and KBr
.

-

Dilute sulfuric acid is basically non-oxidizing, and its interaction with Zn essentially reduces H+
.

Zn+H ₂ SO ₄ (dilute)=ZnSO ₄ +H ₂

The -OH in the sulfuric acid molecule is replaced by other groups to obtain sulfuric acid derivatives
.

The derivative HSO3Cl obtained by replacing one -OH in the H ₂ SO ₄ molecule by chlorine is called chlorosulfonic acid; the derivative SO ₂ C1 _{2 in which} all two -OH of the H ₂ SO ₄ molecule are replaced by chlorine is called Sulfuryl chloride (also known as sulfuryl chloride) .

The dried HCI and SO ₃ react to obtain HSO ₃ Cl
.

SO ₃ +HCI=HSO ₃ Cl

Using activated carbon as a catalyst, SO ₂ and Cl ₂ react to generate SO ₂ Cl ₂
.

SO ₂ +Cl ₂ =SO ₂ Cl ₂

Both SO ₂ Cl ₂ and HSO ₃ Cl are colorless fuming liquids, which hydrolyze violently in water to generate two strong acids
.

3.

Sulfate

Sulfuric acid is a strong acid, and most sulfates are easily soluble in water
.

The insoluble sulfates mainly include CaSO ₄ , SrSO ₄ , BaSO ₄ , PbSO ₄ , Ag ₂ SO ₄ , Hg ₂ SO ₄ and so on

Sulfate crystals with crystal water, such as gypsum CaSO ₄ ·2HO, bile alum CuSO ₄ ·5H ₂ O, green alum FeSO ₄ ·7H ₂ O, halo alum ZnSO ₄ ·7H ₂ O, mirabilite Na ₂ SO ₄ ·10H ₂ O, Epsom salt MgSO ₄ ·7H ₂ O and so on
.

Some crystal water is "anionic crystal water" and some are "coordination water".

Sulfate is easy to form double salt
.

There are two types of common sulfate double salt composition

Another type of double salt is a double salt of sulfate formed by +1-valent cation and +3-valent cation (V ³⁺ , Cr ³⁺ , Fe ³⁺ , Co ³⁺ , Al ^3+, etc.
), the general formula is MI ₂ SO ₄ ·MⅢ ₂ (SO ₄ ) ₃ ·24H ₂ O [or written as MIMⅢ(SO ₄ ) ₂ ·12H ₂ O], such as alum K ₂ SO ₄ ·Al ₂ (SO ₄ ) ₃ ·24H ₂ O, chromium potassium alum K ₂ SO _.
4 · of Cr ₂ (SO _.
4 ) _.
3 · 24H ₂ O and the like
.

Sulfate decomposes when heated, and generally produces metal oxides and SO ₃
.

E.
g

MgSO ₄ =MgO+SO ₃

If the temperature is higher, both SO ₃ and metal oxides may decompose
.
E.
g

4Ag ₂ SO ₄ =8Ag+2SO ₃ +2SO ₂ +3O ₂

If the cation is reductive, it may be oxidized by SO ₃
.

2FeSO ₄ =Fe ₂ O ₃ +SO ₃ +SO ₂

The thermal stability of sulfate can be explained by the theory of ion polarization, which is related to the charge and radius of the cation and the electronic configuration of the cation
.
The radius of the metal ions increases, the polarization ability is weak, the sulfate tends to be stable, and the decomposition temperature increases, such as the decomposition temperature MgSO ₄ <CaSO ₄ <SrSO ₄ ; the higher the metal oxidation number, the stronger the polarization ability, and the salt is unstable.
The decomposition temperature decreases, such as the decomposition temperature Mng(SO ₄ ) ₃ <MnSO ₄ ; the cation of the 18e or (18+2)e configuration is stronger than the cation of the 8e configuration, and the decomposition temperature of the salt is lower, such as the decomposition temperature CdSO ₄ <CaSO ₄
.

4.
Pyrosulfuric acid and its salts

Pure H ₂ SO ₄ , after absorbing SO ₃ , fuming sulfuric acid is obtained.
The chemical formula of fuming sulfuric acid can be written as H ₂ SO ₄ ·xSO ₃
.
When x=1, H ₂ S ₂ O _{7 is} called pyrosulfuric acid
.
H ₂ S ₂ O ₇ can be regarded as the product of removing 1 H ₂ O from 2 H ₂ SO ₄ , so it is also called disulfuric acid .

The most important pyrosulfate is K ₂ S ₂ O ₇ , which is obtained by strong thermal dehydration of KHSO ₄
.

2KHSO ₄ =K ₂ S ₂ O ₇ +H ₂ O

K ₂ S ₂ O _{7 is} eutectic with Al ₂ O ₃ and Cr ₂ O ₃ and other insoluble oxides to form two kinds of sulfates that are soluble in water.
K ₂ S ₂ O ₇ is called molten ore because of its melting effect Agent
.
Obviously, KHSO4 also has a melting effect
.

3K ₂ S ₂ O ₇ +Al ₂ O ₃ =Al ₂ (SO ₄ ) ₃ +3K ₂ SO ₄

Pyrosulfate reacts with water in the solution to slowly generate bisulfate
.

K ₂ S ₂ O ₇ +H ₂ O=2KHSO ₄

Therefore, the pyrosulfate solution should not be stored for a long time, and should be used and prepared now
.