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Mercury

1. Inorganic chemistry
Class -12

2. Mercury
Introduction
Symbol: Hg
Atomic number: 80
Atomic weight: 200
Electronic configuration: [Xe]4f
14
5d
10,
4S
2
Oxidation state: +1, +2
Valency: 1, 2
Occurrence of mercury
It occurs in small quantities in native state
The most important ore of mercury is cinnabar, HgS.

3. Extraction of mercury
Mercury can be obtained from cinnabar, HgS by the following steps:
Concentration
Combined roasting and distillation
Purification

4. 1. Concentration
The ore is crushed with jaw crusher and the powdered ore is concentrated by
froth floatation process
2. Combined roasting and distillation
This is the modern continuous process
The concentrated ore is mixed with charcoal and is heated in shaft furnace to
about 1000
0
C
The cinnabar is first oxidized to mercuric oxide which then decompose into
mercury.
The vapors of mercury distills off, which is condensed in water cooled Y-
shaped condenser.

5. Reactions involved
Roasting:
2HgS + 3O
2→2HgO + 2SO
2
Reduction:
2HgO →2Hg + O
2
2HgO + C →2Hg + CO
2HgO + CO →2Hg + CO2

6. 3. Purification
Mercury obtained by above process is not pure and contains impurities like
Cu, Zn, Bi, Ag etc. as impurities
To remove suspended particles the mercury is filtered through Linen or
chamois leather
The basic metals which are easily oxidized are removed as scums of their
oxides when dust free air is passed through mercury
The filtered Hg is treated with5% HNO
3, where most of basic impurities
dissolve but Hg remains intact
The Hg thus obtained is separated ,washed with water and dried
The mercury still contains impurities like silver gold platinum etc., these are
removed by vacuum distillation where more volatile mercury distilled out
leaving impurities behind.

7. Fig: Purification of mercury
Reactions involved in Purification
6Hg + 8HNO3→2Hg(NO3)2+ 2NO + 4H2O
Zn + HNO3→Zn(NO3)2+ Hg
Fe + HNO3→Fe(NO3)2+ Hg
Fe and Zn as impurities

8. Properties of mercury
Chemical properties
1. Action with air
It is not affected by air or oxygen at ordinary temperature but when heated
at 623k in air, it combines with air forming a red scum of mercuric oxide on
the surface.
2Hg + O
2
623??????
→
2HgO
2. Action with ozone
When exposed to ozone it gets superficially oxidized to mercurous oxide and
loses its meniscus and sticks to the glass. It is called tailing of mercury.
2Hg + O
3 →Hg
2O + O
2

9. 3. Action of aquaregia
Mercury dissolved in aquaregia to form mercuric chloride
HNO
3+ 3HCl →NOCl + 2H
2O + 2Cl
Hg + 2Cl →HgCl
2
4. Action with non-metals
Hg + Cl
2
Δ
→
HgCl
2
Hg + S
Δ
→
HgS
Amalgam
An amalgam is an alloy of mercury with another metal. It may be a liquid, a
soft paste or a solid, depending upon the proportion of mercury. These alloys are
formed through metallic bonding.
It does not form amalgam with iron and platinum thus mercury is stored in iron
bottles.
When little mercury is poured into AgNO
3 solution a tree like growth of silver
amalgam is produced. This is called mercury tree.

10. Mercury poisoning
Mercury poisoning is the result of being exposed to too much mercury, either
through the diet or environment. Mercury is a heavy metal that is highly toxic to
humans. They may include muscle weakness, poor coordination, numbness in the
hands and feet, skin rashes, anxiety, memory problems, trouble speaking, trouble
hearing, or trouble seeing. Long-term complications may include kidney problems
and decreased intelligence.
Uses of mercury
1. It is used in thermometers, barometers etc.
2. It is used in mercury vapor lamps
3. It is used in the extraction of silver and gold
4. It is used in manufacture of caustic soda by castner-kellnercell
5. It is used in the form of amalgams as reducing agent