Electrolysis elements isolated

There have been a number of major episodes in the history of chemistry when half a dozen or so elements were discovered almost at once, or within a period of a few years. Of course, some elements, such as iron, copper, gold, and other metak, have been known since antiquity. In fact, historians and archeologists refer to certain epochs in human history as the Iron Age or the Copper Age. The alchemists added several more elements to the list, including sulfur, mercury, and phosphorus. In relatively modem times, the discovery of electricity enabled chemists to isolate many of the more reactive elements that, imUke copper and iron, could not be obtained by heating their ores with carbon. The English chemist Humphry Davy seized upon the use of electricity or, more specifically, electrolysis to isolate as many as 10 elements, including calcium, barium, magnesium, sodium, and chlorine. 

L. radius, ray) Radium was discovered in 1898 by Mme. Curie in the pitchblende or uraninite of North Bohemia, where it occurs. There is about 1 g of radium in 7 tons of pitchblende. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode on distillation in an atmosphere of hydrogen this amalgam yielded the pure metal. 

The word calcium is derived from calx, the Latin word for lime. The Romans used large quantities of calcium oxide or lime as mortar in constmction (see Lime and limestone). Because calcium compounds are very stable, elemental calcium was not produced until 1808 when a mercury amalgam resulted from electrolysis of calcium chloride in the presence of a mercury cathode. However, attempts to isolate the pure metal by distilling the mercury were only marginally successful. 

The spectacular success (in 1807) of Humphry Davy, then aged 29 y, in isolating metallic potassium by electrolysis of molten caustic potash (KOH) is too well known to need repeating in detail." Globules of molten sodium were similarly prepared by him a few days later from molten caustic soda. Earlier experiments with aqueous solutions had been unsuccessful because of the great reactivity of these new elements. The names chosen by Davy reflect the sources of the elements. 

Metallic manganese was first isolated in 1774 when C. W. Scheele recognized that pyrolusite contained a new element, and his fellow Swede, J. G. Gahn, heated the Mn02 with a mixture of charcoal and oil. The purity of this sample of the metal was low, and high-purity (99.9%) manganese was only produced in the 1930s when electrolysis of Mn solutions was used. 

Sir Humphry Davy (1778-1829) isolated the element by electrolysis of molten caustic soda (NaOH). 

Electrolysis of a solution of the catalyst at — 1.4 V to — 1.5 V vs. SCE in the absence of C02, giving le /Re atom, gave the sparingly soluble green dimer (as characterised by UV-visible, [R, nmr and elemental analysis on the isolated material) in agreement with the work of Lehn and colleagues (Hawecker, 1983) and showing that the first reduction is coupled to the formation of the dimer if chloride loss is allowed to occur. If the cyclic voltammetric scan was reversed when the potential reached —1.5 V, at a... 

Davy also discovered several other elements (potassium, barium, calcium, and strontium) by isolating the metals from their compounds through electrolysis. His work led to the development of electrochemistry, which is the use of electricity as the energy source to break up the oxides of these alkali and alkali earth elements. 

In 1787 William Cruikshank (1745-1795) isolated, but did not identify, strontium from the mineral strontianite he examined. In 1790 Dr. Adair Crawford (1748—1794), an Irish chemist, discovered strontium by accident as he was examining barium chloride. He found a substance other than what he expected and considered it a new mineral. He named the new element strontium and its mineral strontianite after a village in Scotland. In 1808 Sir Humphry Davy treated the ore with hydrochloric acid, which produced strontium chloride. He then mixed mercury oxide with the strontium chloride to form an amalgam alloy of the two metals that collected at the cathode of his electrolysis apparatus. He heated the resulting substance to vaporize the mercury, leaving the strontium metal as a deposit. 

Chemists did not discover the mineral witherite (BaCO ) until the eighteenth century. Carl Wilhelm Scheele (1742—1786) discovered barium oxide in 1774, but he did not isolate or identify the element barium. It was not until 1808 that Sir Humphry Davy used molten barium compounds (baryta) as an electrolyte to separate, by electrolysis, the barium cations, which were deposited at the negative cathode as metallic barium. Therefore, Davy received the credit for bariums discovery. 

Sir Humphry Davy attempted to isolate this unidentified element through electrolysis—but failed. It was not until 1824 that Jons Jakob Berzehus (1779—1848), who had earlier discovered cerium, osmium, and iridium, became the first person to separate the element silicon from its compound molecule and then identify it as a new element. Berzehus did this by a two-step process that basically involved heating potassium metal chips with a form of silica (SiF = silicon tetrafluoride) and then separating the resulting mixture of potassium fluoride and silica (SiF + 4K —> 4KF + Si). Today, commercial production of sihcon features a chemical reaction (reduction) between sand (SiO ) and carbon at temperatures over 2,200°C (SiO + 2C + heat— 2CO + Si). 

Potassium was first isolated as a free metal in 1807 by Sir Humphry Davy. It was the first alkali metal to be discovered, produced by electrolysis of potassium carbonate (potash). The element was earlier called Kalium, derived from the Arabic word qili, meaning grass wort, the ash of which was a source of potash. The element derived its symbol K from Kalium. The English name potassium came from potash (pot ash), the carbonate salt of the metal. 

William Cruickshank in 1787 and Adair Crawford in 1790 independently detected strontium in the mineral strontianite, small quantities of which are associated with calcium and barium minerals. They determined that the strontianite was an entirely new mineral and was different from baryta and other barium minerals known at the time. In 1808, Sir Humphry Davy isolated strontium by electrolysis of a mixture of moist strontium hydroxide or chloride with mercuric oxide, using a mercury cathode. The element was named after the town Strontian in Scotland where the mineral strontianite was found. 

It is interesting that this name, plutonium, had once before been suggested for an element. About 1817 Edward Daniel Clarke (1769— 1822), professor of mineralogy at Cambridge University, suggested that this name be used instead of barium, since barium metal was not unusually heavy. He suggested this name because barium, isolated by electrolysis, owed its existence to the dominion of fire (70). 

Haying failed to isolate the element by the electrolysis of hydrofluoric acid and the fluorides, H. Davy tried if the element could be driven from its combination by double decomposition. He attempted to drive the fluoric principle from the dry fluates of mercury, silver, potassium, and sodium by means of chlorine. He said ... 

We are told by H. Davy that, in 1790, M. Tondi attempted to obtain the constituent elements of these earths by heating a mixture of the oxide with carbon. In some cases he obtained metallic reguli. H. Davy also pointed out that G. E. Stahl approached very nearly to the discovery of the pure alkalies, for he exposed a mixture of solid caustic potash and iron filings to a long-continued heat, and stated that in this way an intensely caustic alkali—valde causticum—is produced. The oxides were not definitely resolved into their elements until 1807, when H. Davy isolated potassium and sodium by the electrolysis of their hydroxides. 

Aluminum is present in most rocks and is the most abundant element in the earth s crust (eight percent by weight.) However, its isolation is very difficult and expensive to accomplish by purely chemical means, as evidenced by the high E° (-1.66 v) of the A13+/A1 couple. For the same reason, aluminum cannot be isolated by electrolysis of aqueous solutions of its compounds, since the water would be electrolyzed preferentially. And if you have ever tried to melt a rock, you will appreciate the difficulty of electrolyzing a molten aluminum ore Aluminum was in fact considered an exotic and costly metal until 1886, when Charles Hall (U.S.A) and Paul Herault (France) independently developed a practical electrolytic reduction process. 

Fluorine is an extremely reactive element, which combines directly or indirectly with nearly all substances. Reactions with elementar fluorine are very violent and sometimes explosions occur so that extreme care must be taken. As the deposition potential of fluorine greatly exceeds the deposition potentials of all other substances, it can be only prepared by electrolysis of its compounds. Due to the fact that water is decomposed by fluorine electrolysis must be effected in an anhydrous medium. Since the days of Moissan who first succeeded in isolating free fluorine, anhydrous hydrofluoric acid is used to prepare it. The electrical conductivity of this substance is very small and must be increased by the addition of alkali fluorides. 

History.—Lithium was identified as an independent element in 1817 by Arfvedson,8 who noted its presence in many minerals and the similarity of its compounds to those of potassium and sodium, but failed to isolate it. Fruitless attempts to obtain the free metal were also made by Davy, Gmelin, and Kralovansky, but in 1855 Bunsen and Matthiessen4 prepared it by electrolysis of the fused chloride. Its name is derived from the Greek Ai0o , a stone. 

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