Periodic Table - Why Mercury Is Poisonous - Essay Example

Periodic Table Mercury was probably known in very early time, though it seems likely that it was discovered after silver, gold, copper, tin and lead. Mercury played an important role in the early work of the alchemists, since it was regarded by many as one of the elements of which all matter is composed. It was given the name "quicksilver" because of its liquid character and its silver-white appearance. Mercury was not recognized as a true metal or as an element until the middle of the eighteenth century. Its Latin name, hydrargyrum, meaning liquid silver, is the source of the symbol Hg. Mercury is one of the noble metals. It appears near the bottom of the activity series and is very inactive. It is not affected by oxygen of the air at ordinary temperatures, but if heated to about 300oC it slowly combines with oxygen to form mercury (II) oxide. It does not dissolve in the monoxidizing acids, but dissolves readily in nitric acid to form mercury (II) nitrate (King, Caldwell and Williams 604).. Mercury was known to the ancient Chinese and Hindus and has been found in 3500 year old Egyptian tombs. Mercury is not usually found free in nature and is primarily obtained from the mineral cinnabar (HgS). Spain and Italy produce about half of the world's supply of Mercury (Gagnon). The element mercury is a metal which is liquid at room temperature. Mercury is a bit like lead but it's liquid. You can hold it in your hand. Heavy (density 13.6), in fact so heavy that objects such as bricks, cannonballs, and lumps of lead or iron will float in Mercury. Gold doesn't float in mercury - it behaves more like sugar in tea! Mercury does not stick to magnets, so if it gets into your carpets or under your floorboards it will be a long-term problem. Mercury vapour makes nice bright lights but is not for breathing. The highly reflective surface of the Mercury makes it the stuff of mirrors. It's also used for thermometers, barometers, electrical devices, etc. However the problem is the cumulative poisonous nature. In the pure metal form it's relatively inert, so not so deadly, but in compounds such as mercuric chloride. Mercury is a liquid it is not wet. It has a negative coefficient of surface tension, which means that the meniscus on the surface is the other way up from normal, or to put it another way it does not soak into material but more runs off in the style of "water off a duck's back (The Element Mercury). Mercury vapor and its salts are poisonous, though the free metal may be taken internally under certain conditions. Because of its relatively low boiling point (629.88 K or 356.73oC or 674.11oF) and hence volatile in nature, free mercury should never be allowed to stand in an open container in the laboratory. Evidence shows that inhalation of its vapors is injurious (King et al. 605). When it comes to versatility, mercury is number one. It has many used for today's common man and mad scientist. Being the only metal which is liquid at room temperature mercury has some specialist uses: It is used in thermometers because it has a large thermal expansion which is constant over a large temperature range although it is being phased out in favour of safer liquids. It is also used in barometers and manometers due to its high density. From this it has also become a way of measuring pressure in millimetres of mercury. Mercury can be used to make thermometers, barometers and other scientific instruments. Mercury conducts electricity and is used to make silent, position dependent switches. Mercury vapor is used in streetlights, fluorescent lamps and advertising signs. Mercury is also a good thermal conductor, making it an excellent shield and coolant in nuclear reactors. Mercury vapor is used instead of steam in the boilers of some turbine (Encyclopedia Britannica). Mercury easily forms alloys with other metals, such as gold, silver, zinc and cadmium. These alloys are called amalgams. Amalgams are used to help extract gold from its ores. Some mercury is used in the preparation of dental amalgams of silver and gold for filling teeth. This process has again been phase out due to health concerns but many people still have mercury containing fillings and crematoria are thought to emit about 5kg of mercury each year simply from dental fillings. The amalgam of 70% silver and 30% tin when mixed with mercury formed a pliable material that could be inserted into the tooth and the amalgam expanded as it dried to fill the entire cavity. However this amalgam has been replaced by a similar one made from 60% silver, 27% tin and 13% copper . Mercury forms useful compounds with other elements. Mercuric chloride (HgCl2) is a very poisonous salt and was once used to disinfect wounds. It is commonly called corrosive sublimate. Since it is very poisonous, it is widely used in dilute solutions (about 1 percent) s a germicide. It was used in large quantities during the World Wars, triggered by the largely increased use of Hg in explosives. Sublimate was also used for preserving wood. Mercurous chloride (Hg2Cl2), also called calomel, is an antiseptic used to kill bacteria. It is also used medicinally as a liver stimulant and cathartic (King et al 612). Mercuric sulfide (HgS) is used to make a red paint pigment called vermilion. Mercuric oxide (HgO) is used to make mercury batteries. Mercury is poisonous and can enter the body through the respiratory tract, the digestive tract or directly through the skin. It accumulates in the body, eventually causing severe illness or death. If taken internally, its action on the kidneys is destructive and causes death. The albumen combines with the mercury (II) ions to form an insoluble white solid. The action of Hg2+ on the protein albumen is like the action of heat on the white of an egg. Swallowing egg white is an antidote for Hg(II) poisoning (King et al. 612). Bibliography "Properties. Occurrence and uses". Encyclopedia Britannica. Gagnon, Steve. "Mercury." Jefferson Lab. 24 November 2007 King, Brooke, Caldwell, William and Williams, Max. College Chemistry. New York: D. Van Nostrand Company, 1977. "The element Mercury:Liquid metal" Read More