Divalent mercury compounds

1.
Oxide

The Hg ²⁺ solution reacts with a strong base to obtain a yellow HgO precipitate
.

Hg ²⁺ + 2OH ^- = HgO + H ₂ O

Hg(NO ₃ ) ₂ thermally decomposes to obtain red HgO
.

2Hg(NO ₃ ) ₂ =2HgO+4NO ₂ +O ₂

At about 350°C, Hg reacts with O ₂ to produce HgO, and the reaction proceeds in the reverse direction above 500°C
.

2Hg+O ₂ =2HgO

HgO shows different colors due to different crystal grain sizes, and yellow HgO particles are smaller
.

The thermal stability of HgO is much lower than that of ZnO and CdO

HgO is basic, soluble in acid but not soluble in alkali
.

HgO+2HC1=HgCl ₂ +H ₂ O

2.
Salt

Mercury nitrate Hg(NO ₃ ) ₂ and mercury sulfate HgSO ₄ are ionic compounds that undergo hydrolysis reaction in water to generate precipitates
.

Therefore, the corresponding acid should be added when preparing Hg(NO ₃ ) ₂ and HgSO ₄ solutions
.

Mercury chloride HgCl ₂ (white), a covalent compound, has a low melting point and is easy to sublime.

It is commonly known as mercury and is highly toxic

HgCl ₂ +H ₂ O=Hg(OH)Cl+HCI

HgI ₂ is red at room temperature, and turns yellow after heating, and is hardly soluble in water
.

A proper amount of SnCl ₂ can reduce HgCl ₂ to Hg ₂ Cl ₂ precipitation; if SnCl _{2 is} excessive, Hg ₂ Cl ₂ will continue to be reduced to metallic mercury
.

The observed phenomenon is that a white precipitate is formed first, then the precipitate gradually turns from white to gray, and finally becomes black

The KI solution was added dropwise to Hg ²⁺ , and a red HgI ₂ precipitate was first produced , and the precipitate was dissolved in the excess KI to produce colorless [HgI ₄ ] ^2-
.

The alkaline solution of [HgI ₄ ] ^2- is called Nessler reagent
.

A small amount of NH ⁴⁺ or NH ₃ in the solution immediately generates a special red precipitate [Hg ₂ ONH ₂ ]I when it meets with Nessler's reagent , which is often used to identify NH ⁴⁺

The red precipitate should not be written as [Hg ₂ NOH ₂ ]I, but can be written as [OHg ₂ NH ₂ ]I
.

Pass H ₂ S into the Hg ²⁺ solution to obtain black HgS (natural cinnabar HgS is red) .

The black HgS can be transformed into a more stable red variant when heated to 386°C .
Mercury sulfide is the least soluble sulfide, insoluble in concentrated nitric acid , but soluble in aqua regia, excessive concentrated Na ₂ S or excessive acidic KI solution

3.

Coordination Compound

Hg ²⁺ and the CN ^- , CF2 ^- , the I ^- , the SCN ^- , NH2 _.

3
and the like generated as a colorless tetrahedral coordination ion
.
Due to the large radius of Hg ²⁺ and the strong polarization ability, the complex formed with the ligand with large deformability is quite stable
.
E.
g

Ammonia water reacts with HgCl ₂ and Hg(NO ₃ ) ₂ solutions to generate white precipitates of mercury ammonium chloride and mercury ammonium nitrate, respectively
.

HgNH ₂ CI solubility than HgNH ₂ NO _.
3
smaller
.
Hg (NH2 ₂ ) in CI NH2 _.
3
-NH _.
4
is substantially insoluble in a mixed solution of CI, dissolved in an excess NH2 _.
3 -NH _.
4 NO _.
3 mixed solution; Hg (NH2 ₂ ) NO _.
3 -soluble NH2 _.
3 -NH _.
4 NO _.
3 mixed Solution
.

To HgC1 ₂ NH was added _.
3 -NH _.
4 NO _.
3 mixed solution with a white precipitate, and the Hg (NO _.
3 ) ₂ solution was added NH _.
3 -NH _.
4 NO _.
3 mixed solution no white precipitate, which generates more [ Hg(NH ₃ ) ₄ ] ₂ ⁺
.

Hg (NO to ₂ ) ₂ KSCN was added, prior white precipitate formed, the precipitate was dissolved in a solution of excess KSCN to give a colorless solution which case a Zn ²⁺ white precipitate, in case of Co ²⁺ to form a blue precipitate
.