Mercury is a naturally occurring chemical element that can be found in rock in the earth’s crust, including coal deposits. Symbol of mercury is Hg and its atomic number is 80. It comes in numerous varieties. It is the only metal which exists in the liquid form at room temperature. Here we will discuss the properties and uses of mercury.
Mercury, like lead and cadmium, is a heavy metal and a component element of earth. In its pure state, it is known as elemental or metallic mercury (written as Hg0). Mercury is never found as pure liquid metal, but rather as compounds and inorganic salts. Mercury can bind to other substances as monovalent or divalent mercury (also known as Hg(I) and Hg(II) or Hg2+). Many inorganic and organic mercury compounds can be generated from Hg (II).
There are three forms of mercury in which it usually exist:
- Elemental mercury
- Inorganic mercury
- Methylmercury and other organic compounds
What is elemental mercury?
Of the three forms of mercury, elemental mercury is the most stable form. Elemental mercury is a shining, silver-white metal that is a liquid at ambient temperature and has long been used in thermometers and electrical switches. If not confined, part of the metallic mercury will evaporate and generate mercury vapors at normal temperature. Mercury vapors have no color and no odor. The more vapors are emitted from liquid metallic mercury as the temperature rises. Some people who have inhaled mercury vapors have reported having a metallic taste in their lips.
Mercury is mined in the form of mercuric sulphide (cinnabar ore). Cinnabar deposits have historically been the source ores for commercial mining of metallic mercury. The metallic form is extracted from mercuric sulphide ore by heating it above 540o C. The mercury in the ore is vaporized and the vapors are captured and cooled to form the liquid metal mercury.
Quicksilver is another name for metallic mercury. It’s found in historical thermometers, fluorescent light bulbs and some electrical switches. When elemental mercury is dropped, it fragments into smaller droplets that can pass through small cracks or get strongly bound to particular materials. Elemental mercury is an element that has not been interacted with anything else. Mercury produces a compound when it reacts with another substance, such as inorganic mercury salts or methylmercury.
What is Inorganic mercury?
Inorganic mercury is abundant in the environment, most notably as the minerals cinnabar and metacinnabar, as well as as impurities in other minerals. Mercury can easily combine with chlorine, sulfur and other elements, forming inorganic salts as a result of weathering. Inorganic mercury salts can be transported and found in soil. Dust containing these salts can enter the atmosphere from mining deposits of mercury-containing ores. Emissions of both elemental and inorganic mercury can occur from coal-fired power plants, the combustion of municipal and medical waste and mercury-using factories.
Mercuric sulphide (HgS), mercuric oxide (HgO) and mercuric chloride are examples of inorganic mercuric compounds (HgCl2). Mercury salts are another name for these mercury compounds. Except for mercuric sulphide, which is red and turns black when exposed to light, most inorganic mercury compounds are white powders or crystals. Some mercury salts are so volatile that they can exist as an atmospheric gas. The water solubility and chemical reactivity of these inorganic or divalent mercury vapors result in significantly faster deposition from the atmosphere than elemental mercury. As a result, the atmospheric lifetimes of these divalent mercury gases are much shorter than those of elemental mercury gas.
Although the use of mercury salts in consumer products, such as medicines, has been phased out, inorganic mercury compounds are still widely used in skin lightening soaps and creams. Mercuric chloride is used in photography, as a topical antiseptic and disinfectant, as a wood preservative and as a fungicide. Mercurous chloride was previously used in medical products such as laxatives, worming medications and teething powders. It has since been replaced by agents that are both safer and more effective. Mercuric sulfide is a red coloring agent used in tattoo dyes and is used to color paints.
What is methylmercury?
When mercury reacts with carbon, the resulting compounds are known as organic mercury compounds or organo-mercurials. There are theoretically many organic mercury compounds such as dimethyl-mercury, phenyl-mercury, ethyl-mercury and methyl-mercury; nonetheless, methylmercury is by far the most frequent organic mercury compound in the environment. Both methyl-mercury and phenyl-mercury exist as salts in the same way that inorganic mercuric substances do. Most forms of methylmercury and phenylmercury are white crystalline solids when pure. Dimethyl-mercury, on the other hand, is a colorless liquid.
When inorganic mercury salts attach to airborne particles. These particles are deposited on land by rain and snow. Even after mercury is deposited on land, it frequently returns to the atmosphere, either as a gas or in the form of particles and then re-deposits elsewhere. Mercury undergoes a number of complex chemical and physical transformations as it travels between the atmosphere, land and water, many of which are not fully understood. Mercury can be converted from an inorganic to an organic state by microscopic organisms combining it with carbon. The most common organic mercury compound found in the environment is methylmercury, which is extremely toxic.
What is cinnabar?
Mercury occurs in environment naturally in the form of HgS, which is named as cinnabar. There are also many other resources of mercury like fossil fuels with trace amount in minerals, contaminated soil, human activities and human made products.
Properties of mercury
Mercury is a naturally occurring compound in the environment. It can be found as a metal, as a salt of mercury, or as organic mercury compounds. It has a silvery color and a high density (13.5 g / cm3) and high surface tension. It is slightly soluble in water and has the ability to dissolve some metals in it, resulting in amalgams. It is a non-combustible liquid that contracts or expands evenly with temperature change.
The boiling point of mercury is 630 K. When it is compared to other metals, mercury is a poor conductor of heat yet a good conductor of electricity as its electrical conductivity is 0.0104 x 106 mho/cm and thermal conductivity value is 0.083 W/cmK. It easily alloys with several metals, including gold, silver and tin. These alloys are known as amalgams. When exposed to air, it evaporates quickly as its heat of vaporization is just 59 KJ/mole. Mercury has three valence states: elemental Hgo, mercureous Hg+1, mercuric Hg2+. However, its ionic forms are Hg2+ and Hg22+.
Mercury enters the environment as a result of the natural breakdown of minerals in rocks and soil caused by wind and water exposure. Mercury emissions from natural sources have remained relatively constant over the years. The most important mercury salts are mercuric chloride HgCl2, mercury fulminate Hg(ONC)2 and mercuric sulphide HgS. Most of the uses of mercury are due to the reason that it has high density and requires less space.
Is mercury toxic?
Metallic mercury is found in a wide range of household items, including barometers, thermometers and fluorescent light bulbs. The mercury in these devices is trapped and does not usually pose any health risks. However, when a thermometer breaks, a significant amount of mercury is released into the atmosphere through breathing for a short period of time as it vaporizes. This can result in nerve, brain, and kidney damage, as well as lung and eye irritation, skin rashes, vomiting and diarrhea.
Mercury has a variety of effects on humans, like nervous system disruption, brain function damage, DNA and chromosomal damage, allergic reactions, which cause skin rashes, fatigue and headaches, harmful reproductive consequences, such as sperm damage, birth defects and miscarriages, learning disabilities, personality changes, tremors, vision changes, deafness, muscle incoordination and memory loss can all result from damaged brain functions. Mongolism is known to be caused by chromosomal damage.
Chronic health effects of mercury include memory loss, inability to concentrate, wings of mood, depression, uncontrollable tumor of hands, eyelids and tongue, spongy gums thus loosening teeth and birth defects in children born to exposed mothers.
Is mercury dangerous for environment?
Besides many uses of mercury, it affects our environment badly. Some such points are enlisted below:
- Mercury from the soil can accumulate in mushrooms.
- Mercury levels in acidic surface waters can be quite high. When the pH of the water is between five and seven, mercury concentrations in the water rise due to mercury mobilization in the ground.
- Once mercury reaches the surface waters or soil, microorganisms can convert it to methyl mercury, a substance that is quickly absorbed by most organisms and is known to cause nerve damage. Every day, fish absorb large amounts of methyl mercury from surface waters. As a result, methyl mercury can build up in fish and the food chains that they are a part of.
- Mercury’s effects on animals include kidney damage, stomach disruption, intestine damage, reproductive failure and DNA alteration.
Uses of mercury
There are numerous uses for mercury metal. Some of which are listed below:
- It is utilized in barometers and manometers due of its high density.
- It is often used in thermometers due to its high rate of thermal expansion, which remains relatively constant throughout a wide temperature range.
- It is employed in the recovery of gold from its ores due to its ease of amalgamation with gold.
- Uses for mercury metal include it as a liquid electrode in the electrolysis of brine to produce chlorine and sodium hydroxide.
- Mercury is still employed in some electrical equipment, such as switches and rectifiers that must be trustworthy, as well as in industrial catalysis.
- Mercury is now used in much lower amounts in consumer batteries and fluorescent lighting, although it has not been completely eradicated.
- Mercury compounds offer a wide range of applications. Calomel (mercurous chloride, Hg2Cl2) is used in electrochemical tests and as a purgative in medicine.
- Mercuric chloride (corrosive sublimate, HgCl2) is a disinfectant, pesticide and rat poison.
- Mercuric oxide is a component in skin ointments.
- In organic chemistry, mercuric sulphate is employed as a catalyst.
- Vermilion, a red pigment, is mercuric sulphide; black is another crystalline form of the sulphide that is also employed as a pigment. As a detonator, mercury fulminate, Hg(CNO)2, is utilized.
- Other uses of mercury include formation of fluorescent light bulbs, alkaline batteries, jewelry, extraction of gold from silver and polarography.