Introduction to Mercury

Mercury

The basic information about mercury is given as:

The compounds of mercury are:

Hydrides

The term hydride mean compounds of the type M_xH_y and not necessarily to indicate that any compounds listed behave as hydrides chemically.

• Mercury dihydride: HgH₂

Fluorides

• Mercury difluoride: HgF₂
• Dimercury difluoride: Hg₂F₂

Chlorides

• Mercury dichloride: HgCl₂
• Dimercury dichloride: Hg₂Cl₂

Bromides

• Dimercury dibromide: Hg₂Br₂

Iodides

• Mercury diiodide: HgI₂
• Dimercury diiodide: Hg₂I₂

• Mercury telluride: HgTe

Complexes

• Dimercury dinitrate dihydrate: Hg₂(NO₃)₂.2H₂O

Ores

Cinnabar → HgS

Livingstonite → HgSb

Extraction

• Concentration: at first, the ore is crushed into fine pieces and then powdered into the ball mills. The concentrated ore is then subjected to froth flotation method.
• Roasting and distillation: the concentration is first mixed with 2% coke and then fed into shaft furnace. The furnace is heated and excess air is blown in. The ore is roasted and forms the mercuric oxide. The mercuric oxide decomposes to mercury. The vapor of mercury distils off along with other gases into a condenser which condenses Y-shaped water cooled pipe.

$$2HgS+3O_2\longrightarrow 2HgO+2SO_2$$

$$2HgO\longrightarrow 2Hg+O_2$$

$$HgO+C\longrightarrow Hg+CO$$

• Purification

1. Filtration: in this method mercury is passed through chamois leather or thick canvas to remove sustained impurities.
2. Treatment with 5% dilutes HNO₃: when impure mercury is passed through the long glass tube containing 5% HNO₃, metal impurities are dissolved to give their nitrate or react with nitrate of mercury leaving behind pure mercury.

$$4Zn+10HNO_3\longrightarrow 4Zn(NO_3)_2+5H_2O+N_2O$$

$$6Hg+8HNO_3\longrightarrow 3Hg_2(NO_3)_2+4H_2O+2NO$$

$$Hg_2(NO_3)_2+Zn\longrightarrow 2Hg+Zn(NO_3)_2$$

The mercury thus obtained may contain Au, Ag, Pt impurities which are removed by vacuum distillation and finally pure Hg is obtained.

Physical properties

• It is the heaviest metal at ordinary temperature.
• It is silvery-white liquid.
• It is highly poisonous.

Chemical properties

• Action with air: it forms a mercuric oxide when reacted with air at a temperature of 623K.

$$Hg+O_2\longrightarrow HgO$$

• Action with aquaregia: mercury gets dissolved when reacted with aquaregia.

$$HNO_3+3HCl+Hg\longrightarrow NOCl+HgCl_2+2H_2O$$

• Action with sulphur: it reacts with sulphur to form a mercuric sulphide.

$$Hg+S\longrightarrow HgS$$

• Reaction with metal: it reacts with metals to form the amalgam.

$$Zn+Hg\longrightarrow ZnHg (formation\space of\space zinc\space amalgam)$$

$$Na+Hg\longrightarrow NaHg (formation\space of\space sodium\space amalgam)$$

• Reaction with halogen: It reacts with halogens to form halides.

$$Hg+Cl_2\longrightarrow HgCl_2 (limited\space amount\space of \space mercury)$$

$$Hg+Cl_2\longrightarrow Hg_2Cl_2 (excess\space amount\space of \space mercury)$$

• Tailing of mercury: when mercury is exposed to ozone, it superficially gets oxidized and loses its meniscus, it is called tailing of mercury. During this process dark grey colored tail of mercurous oxide is formed.

$$2Hg+O_3\longrightarrow Hg_2O+O_2$$

Uses

• Mercury is used in thermometer, barometer.
• Mercury is used for making an amalgam.

Mercury poisoning

Mercury and it’s compound are highly poisonous or toxic, so this should be handled safely to prevent absorption by inhalation, ingestion and through the skin. It may cause deafness, madness, lung damage, brain damages, and even death. Mercury vapors are toxic because if inhaled it passes to the bloodstream, digestive system, lungs and then transported to the brain.

The industries which manufacture acetaldehyde and polyphenyl chloride in Minamata used mercury compound as the catalyst. They released their effluent in Minamata bay. That mercury compound is was taken by plankton, fishes eat plankton. The people of Minamata consumed such fast and suffered from diseases.

Uses

• Mercury is an interesting thing to study upon for a very long time as a heavy liquid metal. However, because of its toxicity, many uses of mercury are being phased out or are under review.

• Mercury is used as catalysts in industries. It is also used in some electrical appliances.

• Previously it uses was in the manufacture of sodium hydroxide and chlorine. It was genuinely used in many appliances like batteries, fluorescent lights, thermometers, and barometers. New technologies are replacing them.

• ,The alloy of mercury is called amalgam with other metals such as gold, silver, and tin. Mercury amalgamates with gold helped mankind in recovering gold from its ores. Mercury amalgams were also used in dental fillings.
• Mercuric sulfide is a bright-red paint pigment, but since it is a very toxic element it should be handled with great care

• Mercury has no known biological role but is present in every living thing and widespread in the environment. Mercury is even present in every single food we intake in our daily life.

Natural abundance

Mercury rarely found in the pure state in nature, but can be found as droplets in cinnabar (mercury sulfide) ores.Mainly mercury is found in China and Kyrgyzstan. The metal is obtained by heating cinnabar in a current of air and condensing the vapor.

Reference

pulse, Tracy. Introduction to chemistry. u.s.a: flex book, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. Kathmandu: Vidhyarthi Pustak Bhandar, 2012.