Chemical reactions

Reaction of mercury with acids

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)

Reaction of mercury with air

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]

Reaction of mercury with bases

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.

Reaction of mercury with halogens

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)

Reaction of mercury with metals/metal ions

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)

Reaction of mercury with sulfide

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)

Reaction of mercury with sulfur

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

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

Reaction of mercury with water

Metallic mercury does not react with water under normal conditions.

Qualitative analysis

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)

Quantitative analysis

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