Mercury

Mercury does not react hydrochloric acid. It does dissolve in cold nitric acid and hot concentrated sulfuric acid, and at excess acid, mercury(II) salts are formed [13]:

3 Hg(l) + 8 H⁺(aq) + 2 NO₃⁻(aq) 3 Hg²⁺(aq) + NO(g) + 4 H₂O(l)
Hg(l) + 2 H₂SO₄(aq) Hg²⁺(aq) + SO₄²⁻(aq) + SO₂(g) + 2 H₂O(l)

Mercury does not react with oxygen at ordinay temperatures. When heated it slowly oxidizes, forming mercury(II) oxide [13]:

2 Hg(l) + O₂(g) 2 HgO(s) [red]

Metallic mercury does not react with alkalis under normal conditions.

Hg(I) as Hg₂²⁺ reacts with hydroxide, forming Hg₂O.

Hg₂²⁺(aq) + 2 OH⁻(aq) Hg₂O(s) [black]

The precipitate is split up in HgO and Hg upon heating

Hg₂O(s) HgO(s) + Hg(l)


Hg(II) reacts with hydroxide under cold conditions, forming a yellow precipitate of HgO

Hg²⁺(aq) + 2 OH⁻(aq) HgO(s) [yellow] + H₂O(l)

Upon heating, the precipitate turns red.

Mercury metal reacts with F₂, Cl₂, Br₂, or I₂, to form the corresponding dihalides [13].

Hg(l) + F₂(g) HgF₂(s) [white]
Hg(l) + Cl₂(g) HgCl₂(s) [white]
Hg(l) + Br₂(l) HgBr₂(s) [white]
Hg(l) + I₂(s) HgI₂(s) [red]


Hg(I) is precipitated by Cl⁻ ions, forming Hg₂Cl₂:

Hg₂²⁺(aq) + 2 Cl⁻(aq) Hg₂Cl₂(s) [white]


Mercury(II) chloride is moderately soluble in water. In excess Cl⁻, a tetrachloromercurate(II) ion is formed [13]:

HgCl₂(aq) + 2 Cl⁻(aq) [HgCl₄]²⁻(aq)


Hg(II) is precipitated by I⁻ ions, forming HgI₂ [13]:

Hg²⁺(aq) + 2 I⁻(aq) HgI₂(s) [red]

The precipitate is dissolved in excess I⁻, forming the almost colorless tetraiodo mercurium complex [13]:

HgI₂(s) [red] + 2 I⁻(aq) [HgI₄]²⁻(aq)

Hg²⁺ is reduced to Hg by Cu, forming Hg and Hg(I):

Hg²⁺(aq) + Cu(s) Hg(l) + Cu²⁺(aq)


Hg(II) is reduced to Hg(I) by elemental Hg [13]:

Hg²⁺(aq) + Hg(l) Hg₂²⁺(aq)


Under acidic conditions and in the presence of chloride ions, Hg(II) is reduced to Hg(I) by Sn(II), forming Hg₂Cl₂:

Hg²⁺(aq) + Sn²⁺(aq) + 2 Cl⁻(aq) Hg₂Cl₂(s) + Sn⁴⁺(aq)

Hg₂²⁺ is reduced to Hg by Sn(II). This reaction is used for qualitative analysis for Sn(II):

Hg₂²⁺(aq) + Sn²⁺(aq) 2 Hg(l) + Sn⁴⁺(aq)

In excess Sn(IV), Hg(I) is reduced to Hg:

Hg₂Cl₂(s) + Sn²⁺(aq) 2 Hg(l) + Sn⁴⁺(aq) + 2 Cl⁻(aq)

Hg(I) in the form of Hg₂²⁺ is precipitated by H₂S [13]:

Hg₂²⁺(aq) + H₂S(aq) + 2 H₂O(l) Hg₂S(s) + 2 H₃O⁺(aq) HgS(s) [black] + Hg(l) + 2 H₃O⁺(aq)

The precipitate can be dissolved in a mixture of sodium sulfide and sodium disulfide

HgS(s) + Hg(l) + S²⁻(aq) + S₂²⁻(aq) 2 [HgS₂]²⁻(aq)


Hg(II) is precipitated by H₂S as HgS. During the process, white, yellow and brown intermediates may be observed.

Hg²⁺(aq) + H₂S(aq) HgS(s) [black] + 2 H⁺(aq)

The precipitate can only be dissolved in aqua regis, sodium hypochlorite under acidic conditions, or Na₂S under alkaline conditions

3 HgS(s) + 12 Cl⁻(aq) + 8 H⁺(aq) 3 [HgCl₄]²⁻(aq) + 2 NO(g) + 3 S(s) + 4 H₂O(l)
HgS(s) + ClO⁻(aq) + 2 H⁺(aq) + 3 Cl⁻(aq) [HgCl₄]²⁻(aq) + S(s) + H₂O(l)
HgS(s) + S²⁻(aq) [HgS₂]²⁻(aq)

Mercury reacts with sulfur, forming mercury(II) sulfide [13]:

Hg(l) + S(s) HgS(s)

Metallic mercury does not react with water under normal conditions.

Hg(I) is precipitated by Cl⁻ ions, forming Hg₂Cl₂:

Hg₂²⁺ (aq) + 2 Cl⁻(aq) Hg₂Cl₂(s) [white]

The precipiptate is treated with ammonia, forming a mixture of white HgNH₂Cl and evenly distributed black Hg:

Hg₂Cl₂(s) [white] + 2 NH₃(aq) HgNH₂Cl(s) + Hg(l) + NH₄⁺(aq) + Cl⁻(aq)

Method 3500-Hg B Cold Vapour Atomic Absorption Method [6]. Elemental mercury is liberated by hydrochloric acid and stannous chloride. Vapours are purged into a cold vapour cell on the atomic absorption spectrophotometer and quantified using a wavelength of 257.3 nm.

Method limit of detection in water = 0.0001 mg/L
Method limit of detection in soil = 0.01 mg/kg