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Agustus 26, 2011

TITRASI PROTOLIT LEMAH

Agustus 26, 2011 0
Titrasi protolit lemah lebih sulit dan lebih rumit daripada titrasi protolit kuat. Daerah kesetaraannya jauh lebih sempit, sehingga persyaratan titrasi hanya dapat dilihat secara tepat dari kurva teoritis.
Perubahan pH yang tajam terlihat di sekitar titik kesetaraan seperti terlihat pada Gambar.2.
Asam asetat merupakan salah satu contoh protolit lemah yang kesetimbangn asam basanya ditentukan oleh tetapan protolisisnya. Karena itu bentuk kurva titrasinya sangat bergantung pada tetapan titik ini. Titik-titik khas kurva titrasinya mudah ditentukan dari bagan LK.
Download versi lengkapnya DI SINI

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 26, 2011

Agustus 24, 2011

Penentuan Kadar Sukrosa pada Minuman

Agustus 24, 2011 2
Sukrosa atau gula tebu adalah disakarida dari glukosa dan fruktosa. Sukrosa dibentuk oleh banyak tanaman, tetapi tidak terdapat pada hewan tingkat tinggi. Berlawanan dengan maltosa dan laktosa, sukrosa tidak mengandung atom carbon anomer bebas, karena carbon anomer kedua komponen unit monosakarida pada sukrosa berikatan satu dengan yang lain.



sukrosa [O-β-D-fruktofuranosil-(2→1)-α-D-glukofiranosida]

Karena alasan inilah sukrosa buka merupakan gula pereduksi. Walaupun D-glukosa merupakan unit pembangun utama kedua senyawa pati dan selulosa, sukrosa merupakan produk fotosintesis antara yang utama. Pada banyak tanaman sukrosa merupakan bentuk utama dalam transport gula dari daun ke bagian-bagian lain tanaman melalui system paskular. Keuntungan sukrosa dibandingkan dengan D-glukosa sebagai bentuk transport gula mungkin karena atom karbon anomernya berada dalam keadaan terikat, jadi, melindungi sukrosa dari serangan oksidatif atau hidrolitik oleh enzim-enzim tanaman sampai molekul ini mencapai tujuan akhirnya di dalam tanaman.

Hewan tidak dapat menyerap sukrosa seperti pada tanaman, tetapi dapat menyerap molekul tersebut dengan bantuan enzim suknosa, yang juga disebut sebagai invertase, yang terdapat di dalam sel yang membatasi dinding usus kecil. Enzim ini mengkatalisa hidrolisis sukrosa menjadi D-gukosa dan D-fruktosa, yang segera teserap ke dalam aliran darah.

Sukrosa merupakan disakarida yang paling manis diantara ketiga jenis disakarida yang umum dijumpai. Sukrosa juga lebih manis dari glukosa

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 24, 2011

Agustus 21, 2011

PENAMAAN SENYAWA POLIATOM, ASAM DAN BASA

Agustus 21, 2011 0

Senyawa poliatom

Senyawa poliatom merupakan senyawa yang dibentuk dari ion poliatomik. Pada ion poliatomik, dua atau lebih aom-atom bergabung bersama-sama dengan ikatan kovalen. Penamaan senyawa poliatom ini adalah dengan cara mengurutkan nama kation dan anionnya.
Contoh:
NaCN : natrium sianida
CaCO3 : kalsium karbonat
K2SO4 : kalium sulfat
NH4Cl : ammonium klorida

Senyawa asam

Ahli kimia mempunyai beberapa cara untuk mendefinisikan senyawa sebagai suatu asam. Menurut Arrhenius istilah senyawa asam sebagai zat yang menghasilkan ion hidrogen (H+) ketika dilarutkan ke dalam air. Senyawa asam biner merupakan senyawa gabungan H dengan atom-atom nonlogam lainnya. Adapun penamaan senyawa asam biner adalah:
a. Unsur hidrogen diikuti dengan nama unsur + ida, atau
b. Awalan asam diikuti nama unsur + ida, atau
c. Awalan asam diikuti dengan nama unsur dengan awalan ”hidro” dan akhiran ”ida”.
Contoh:
HF : asam fluorida
HCl : asam klorida
HBr : asam bromida

Senyawa basa


Menurut Arrhenius basa adalah zat yang dapat menghasilkan ion hidroksida (OH-) jika dilarutkan dalam air. Senyawa basa merupakan senyawa ion yang terdiri dari kation logam dan anion OH- kecuali (NH4OH). Adapun penamaan senyawa basa adalah: nama logam + hidroksida
Contoh:
LiOH : litium hidroksida
NaOH : natrium hidroksida
Ca(OH)2 : kalsium hidroksida

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 21, 2011

Agustus 20, 2011

Menentukan Massa Molar Cairan atau Gas

Agustus 20, 2011 0
Banyak pengukuran gas atau cairan memperlihatkan bahwa pada tekanan rendah; tekanan, volume, temperature, dan jumlah gas/cairan dihubungkan dengan persamaan PV = MRT. Persamaan ini merupakan hubungan antara dua variable sampel suatu zat, dan disebut persamaan keadaan gas sempurna. Tetapi beberapa perlakukan praktikum, beberapa cairan diasumsikan seperti gas sempurna untuk mempermudahkan perhitungan.

Persamaan di atas cukup dipenuhi oleh kebanyakan gas pada temperature dan tekanan kamar (mendekati 25oC dan 1 atm). Semua gas semakin mematuhi persamaan tadi ketika tekanan berkurang. Dengan demikian persamaan di atas adalah hukum pembatas dengan pengertian bahwa semua gas mematuhinya pada batas tekanan nol. Gas yang mematuhi persamaan gas di atas secara tepat disebut persamaan gas sempurna atau gas ideal. Gas nyata adalah gas yang sebenarnya seperti hydrogen, oksigen, atau udara yang tidak mematuhi persamaan gas ideal dengan tepat kecuali pada batas tekanan nol.

Nilai konstanta gas dapat diperoleh dengan mengevaluasi PV/nT untuk gas pada batas tekanan nol (untuk menjamin bahwa gas itu berperilaku seperti gas sempurna).
Dua kumpulan kondisi kini digunakan sebagai nilai standar pelaporan data. Kondisi pertama adalah temperature dan tekanan standar (STP), yang sesuai dengan 0oC dan 1 atm, dan kondisi kedua adalah temperature dan tekanan kamar standar (STAP) yang sesuai dengan 25oC (lebih tepatnya 298,15K) dan 1 bar (Po).

STP : V = 22,414 L/mol
STAP : V = 24,790 L/mol

Kita lambangkan volume molar pada STAP dengan Vo . jika persmaan pertama tadi diturunkan, maka diperoleh hubungan

Mr = ρ RT/P;

yaitu terdapat hubungan antara massa molar dengan massa jenis zat.
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Rino Safrizal
Jejaring Kimia Updated at: Agustus 20, 2011

Agustus 14, 2011

Titanium [Ti]

Agustus 14, 2011 0

Characteristics

An: 22 N: 26
Am: 47.867 g/mol
Group No: 4
Group Name: Transition metals
Block: d-block Period: 4
State: solid at 298 K
Colour: silvery metallic
Classification: Metallic
Boiling Point: 3560K (3287oC)
Melting Point: 1941K (1668oC)
Superconducting temperature: 0.40K (-272.7°C)
Density: 4.506g/cm3

Discovery Information

Who: William Gregor
When: 1791
Where: England

Name Origin

Greek: titanos (Titans). "Titanium" in different languages.

Sources

Usually occurs in the minerals ilmenite (FeTiO3) or rutile (TiO2). Also in Titaniferous magnetite (Fe3O4), titanite (CaTiSiO5), and iron ores. The primary deposits of titanium ore are in Australia, Scandinavia, North America and Malaysia.

 
A large piece of rutile, a mineral source of titanium.
World wide production is around 99 thousand tons.

Abundance

Universe: 3 ppm (by weight)
Sun: 4 ppm (by weight)
Carbonaceous meteorite: 550 ppm
Earth’s Crust: 6600 ppm
Seawater: 4.8 x 10-4 ppm

Uses

Titanium is well known for its excellent resistance to corrosion; it is almost as resistant as platinum, being able to withstand attack by acids, moist chlorine gas, and by common salt solutions.
Because of its high tensile strength (even at high temperatures), light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures, titanium alloys are used in aircraft (a Boeing 737 contains around 18 tons, a 777 around 58 tons), armour plating, naval ships, spacecraft and missiles. It is used in steel alloys to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content. Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum and with other metals.
Because it is considered to be physiologically inert, the metal is used in joint replacement implants such as hip ball and sockets and to make medical equipment and in pipe/tank lining in food processing. Since titanium is non-ferromagnetic patients with titanium implants can be safely examined with magnetic resonance imaging, which makes it convenient for long term implants and surgical instruments for use in image-guided surgery.
95% of titanium production is consumend in the form of titanium dioxide (TiO2), a white pigment that covers surfaces very well, is used in paint, rubber, paper and many other materials. Also used in heat exchangers, airplane motors, bone pins and other things requiring light weight metals or metals that resist corrosion or high temperatures. Titanium oxide is used extensively in paints and in suncreens.
Due to excellent resistance to sea water, it is used to make propeller shafts and rigging and in the heat exchangers of desalination plants and in heater-chillers for salt water aquariums, and lately diver knives as well.
Titanium tetrachloride (TiCl4), a colourless liquid, is used to iridize glass and because it fumes strongly in moist air it is also used to make smoke screens and in skywriting.

History

Titanium was discovered combined in a mineral in Cornwall, England in 1791 by amateur geologist William Gregor, the then vicar of Creed village. He recognized the presence of a new element in ilmenite (FeTiO3) when he found black sand by a stream in the nearby parish of Manaccan and noticed the sand was attracted by a magnet. Analysis of the sand determined the presence of two metal oxides; iron oxide (explaining the attraction to the magnet) and 45.25% of a white metallic oxide he could not identify. Gregor, realizing that the unidentified oxide contained a metal that did not match the properties of any known element, reported his findings to the Royal Geological Society of Cornwall and in the German science journal Crell’s Annalen.
Around the same time, Franz Joseph Muller also produced a similar substance, but could not identify it. The oxide was independently rediscovered in 1795 by German chemist Martin Heinrich Klaproth in rutile from Hungary. Klaproth found that it contained a new element and named it for the Titans of Greek mythology. After hearing about Gregor’s earlier discovery, he obtained a sample of manaccanite and confirmed it contained titanium.
The processes required to extract titanium from its various ores are laborious and costly; it is not possible to reduce in the normal manner, by heating in the presence of carbon, because that produces titanium carbide. Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter by heating TiCl4 with sodium in a steel bomb at 700 - 800oC in the Hunter process. Titanium metal was not used outside the laboratory until 1946 when William Justin Kroll proved that it could be commercially produced by reducing titanium tetrachloride with magnesium in what came to be known as the Kroll process. Although research continues into more efficient and cheaper processes (FFC Cambridge, e.g.), the Kroll process is still used for commercial production.
Titanium of very high purity was made in small quantities when Anton Eduard van Arkel and Jan Hendrik de Boer discovered the iodide, or crystal bar, process in 1925, by reacting with iodine and decomposing the formed vapours over a hot filament to pure metal.

Notes

Pure titanium is a lustrous white metal, as strong as steel, 45% lighter, 60% heavier than aluminium.
Titanium is Latin and refers to the Titans, the first sons of the earth in Mythology. It was discovered by Gregor in 1791 and named by Klaproth four years later. It was nearly a hundred years later (1887) when impure titanium was first prepared by Nilson and Pettersson. About 20 years later Hunter heated Titanium Chloride TiCl4 with sodium in a steel bomb and isolated 99.6% pure titanium. It is the ninth most abundant element in the Earth’s crust and is also found in meteorites and in the sun. It is found in the ash of coal, in plants and even in the human body. It occurs in the minerals rutile (TiO2), ilmenite (FeTiO3) and sphene (CaTiSiO5).
As a compound, it is found as Titanium dioxide TiO2 in star sapphires and rubies (it is TiO2 that gives them their asterism). It is also found as titanium chloride (TiCl4). When it is red hot the metal combines with oxygen, and when it reaches 550oC it combines with chlorine. It also reacts with the other halogens and absorbs hydrogen.

Hazards

As a powder or in the form of metal shavings, titanium metal poses a significant fire hazard and, when heated in air, an explosion hazard. Water and carbon dioxide-based methods to extinguish fires are ineffective on burning titanium.
Titanium powder is harmful if inhaled and is also an eye irritant.

Titanium Compounds

Titanium boride TiB2

An extremely hard ceramic material with excellent corrosion resistance at high temperatures and very good wear resistance which does not occur naturally in earth. Many TiB2 applications are inhibited by economic factors, particularly the costs of densifying a high melting point material. Current use of this material appears to be limited to specialized applications in such areas as impact resistant armour, cutting tools, crucibles and wear resistant coatings.

Titanium carbide TiC

An extremely hard refractory ceramic material, similar to tungsten carbide. It is commercially used in tool bits cutting tools. It is mainly used in preparation of cermets, which are frequently used to machine steel materials at high cutting speed.

Tool bits without tungsten content can be made of titanium carbide in nickel-cobalt matrix cermet, enhancing the cutting speed and precision and smoothness of the workpiece. This material is sometimes called high-tech ceramics and is used as a heat shield for atmospheric re-entry of space shuttles and similar vehicles. The substance may be also polished and used in scratch-proof watches.

Titanium dioxide TiO2

Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index, in which it is surpassed only by a few other materials. When deposited as a thin film, its refractive index and colour make it an excellent reflective optical coating for dielectric mirrors. TiO2 is also an effective opacifier in powder form, where it is employed as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, and most toothpastes. In cosmetic and skin care products, titanium dioxide is used both as a pigment and a thickener, and in almost every sunblock with a physical blocker, titanium dioxide is found both because of its refractive index and its resistance to discolouration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Titanium dioxide is used as a white food dye. In that use, its E number is E171.

Titanium nitride TiN

An extremely hard ceramic material, often used as a coating on titanium alloy, steel, carbide, and aluminium components to improve the substrate’s surface properties. Far and away the most common use for TiN coating is for edge retention and corrosion resistance on machine tooling, such as drill bits and milling cutters, often improving their lifetime by a factor of three or more.

Because of its metallic gold colour, it is used to coat costume jewellery and automotive trim for decorative purposes. TiN is also widely used as a top-layer coating, usually with nickel or chromium plated substrates, on consumer plumbing fixtures and door hardware.

Reactions of Titanium

Reactions with water

Titanium is coated with a thin oxide layer that under normal circumstances renders inert in air. However, titanium will react with steam to form titanium(IV) oxide and hydrogen.
Ti(s) + 2H2O(g) --> TiO2(s) + 2H2(g)


Reactions with air

Titanium is coated with a thin oxide layer that under normal circumstances renders inert in air. However, once titanium starts to burn in air it burns with a bright white flame to form titanium oxide and titanium nitride. It will burn in pure nitrogen to form titanium nitride.
Ti(s) + O2(g) --> TiO2(s)

2Ti(s) + N2(g) --> TiN(s)


Reactions with halogens

Titanium does react with the halogens upon warming to form titanium(IV) halides. The reaction with fluorine requires heating to 200oC.
Ti(s) + 2F2(g) --> TiF4(s)
Ti(s) + 2Cl2(g) --> TiCl4(s)
Ti(s) + 2Br2(l) --> TiBr4(s)
Ti(s) + 2I2(s) --> TiI4(s)

Reactions with acids

Dilute aqueous hydrofluoric acid reacts with titanium to form the complex anion [TiF6]3- together with hydrogen.
2Ti(s) + 12HF(aq) --> 2[TiF6]3-(aq) + 3H2(g) + 6H+(aq)

Titanium metal does not react with mineral acids at ambient temperature but does react with hot hydrochloric acic to form titanium(III) complexes.

Reactions with bases

Titanium does not appear to react wih alkalis under normal conditions, even when hot.

Occurrence of Titanium

Titanium is always bonded to other elements in nature. It is the ninth-most abundant element in the Earth’s crust (0.63% by mass) and the seventh-most abundant metal. It is present in most igneous rocks and in sediments derived from them (as well as in living things and natural bodies of water). In fact, of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium. Its proportion in soils is approximately 0.5 to 1.5%.
It is widely distributed and occurs primarily in the minerals anatase, brookite, ilmenite (FeTiO3), perovskite, rutile (TiO2), titanite ( CaTiSiO5) (sphene), as well in many iron ores. Of these minerals, only rutile and ilmenite have any economic importance, yet even they are difficult to find in high concentrations. Significant titanium-bearing ilmenite deposits exist in western Australia, Canada, New Zealand, Norway, and Ukraine. Large quantities of rutile are also mined in North America and South Africa and help contribute to the annual production of 90,000 tonnes of the metal and 4.3 million tonnes of titanium dioxide. Total known reserves of titanium are estimated to exceed 600 million tonnes.
Titanium is contained in meteorites and has been detected in the sun and in M-type stars; the coolest type of star with a surface temperature of 3,200oC (5792oF). Rocks brought back from the moon during the Apollo 17 mission are composed of 12.1% TiO2. It is also found in coal ash, plants, and even the human body.

Isotopes of Titanium

44Ti [22 neutrons]

Abundance: synthetic
Half life: 63 years [ Electron Capture ]
Decay Energy: ? MeV
Decays to 44Sc.
Half life: 63 years [ Gamma Radiation ]
Decay Energy: 0.07D, 0.08D MeV
Decays to ?.

46Ti [24 neutrons]

Abundance: 8.0%
Stable with 24 neutrons

47Ti [25 neutrons]

Abundance: 7.3%
Stable with 25 neutrons

48Ti [26 neutrons]

Abundance: 73.8%
Stable with 26 neutrons

49Ti [27 neutrons]

Abundance: 5.5%
Stable with 27 neutrons

50Ti [28 neutrons]

Abundance: 5.4%
Stable with 28 neutrons

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 14, 2011

RUTILE [ Oxides and Hydroxides : Rutile ]

Agustus 14, 2011 0

TiO2, titanium Oxide: Ore of titanium, pigment and as an ornamental stone when in clear quartz

Rutile is an nteresting, varied and important mineral. Rutile is a major ore of titanium, a metal used for high tech alloys because of its light weight, high strength and resistance to corrosion. Rutile is also unwittingly of major importance to the gemstone markets. It also forms its own interesting and beautiful mineral specimens. Microscopic inclusions of rutile in quartz, tourmaline, ruby, sapphire and other gemstones, produces light effects such as cat’s eye and asterisms (stars). A beautiful stone produced by large inclusions of golden rutile needles in clear quartz is called rutilated quartz.
Rutilated quartz is sometimes used as a semi-precious stone and/or for carvings. This stone is produced because at high temperatures and pressure, n(SiO2)-n(TiO2) is in a stable state but as temperatures cool and pressure eases the two separate with rutile crystals trapped inside the quartz crystals. Twinning is common in rutile crystals, with a cyclic twin forming that is comprised of six or even eight "twins" arranged in a circle. A Rutile Star is a formation of crystals of rutile in a six rayed orientation. The crystals grow off of a hematite crystal and the orientation is caused by its six rhombic faces.

Physical Characteristics

Colour: black or reddish brown in large thick crystals or golden yellow or rusty yellow as inclusions or in thin crystals

Luster: adamantine to submetallic
Transparency: Crystals are transparent in rather thin crystals otherwise opaque

Crystal System: tetragonal; 4/m 2/m 2/m
Crystal Habits: include eight sided prisms and blocky crystals terminated by a blunt four sided or complex pyramid. The prisms are composed of two four sided prisms with one of the prisms being dominant. Crystals with some twins forming hexagonal or octahedral circles. A very common habit is thin acicular needles (especially as inclusions in other minerals) or as blades

Cleavage: good in two directions forming prisms, poor in a third (basal)

Fracture: conchoidal to uneven

Hardness: 6 - 6.5

Specific Gravity: 4.2+ (slightly heavy)

Streak: brown

Other: Striations lengthwise on crystals, high refractive index (2.63) gives it a sparkle greater than diamond (2.42)
Associated Minerals: quartz, tourmaline, barite, hematite and other oxides and silicates

Major Occurrences: include Minas Gerias, Brazil; Swiss Alps; Arkansas, USA and some African locallities

Best Indicators: crystal habit, streak, hardness, colour and high index of refraction (luster)
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Rino Safrizal
Jejaring Kimia Updated at: Agustus 14, 2011

Agustus 09, 2011

Gold [Au]

Agustus 09, 2011 0

Characteristics

An: 79 N: 118
Am: 196.96655 g/mol
Group No: 11
Group Name: Coinage metal
Block: d-block Period: 6
State: solid at 298 K
Colour: gold (!) Classification: Metallic
Boiling Point: 3129K (2856oC)
Melting Point: 1337.33K (1064.18oC)
Density: 19.3g/cm3

Discovery Information

Who: Known to the ancients. Gold has been known and highly valued since prehistoric times. It may have been the first metal used by humans and was valued for ornamentation and rituals. Eqyptian hieroglyphs from as early as 2600BC mention gold. The south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world’s earliest coinage in Lydia between 643 and 630 BC.

Name Origin

Gold from old English word geolo (yellow); Au from Latin: aurum (gold). "Gold" in different languages.

Sources

Found in veins in the crust, with copper ore and natively. Major producers include South Africa, Canada, the United States and Western Australia.
Around 1400 tons are produced each year.

Abundance

Universe: 0.0006 ppm (by weight)
Sun: 0.001 ppm (by weight)
Carbonaceous meteorite: 0.17 ppm
Earth’s Crust: 0.011 ppm
Seawater: 5 x 10-5 ppm
Human: 100 ppb by weight; 3 ppb by atoms

Uses

Pure gold is too soft for ordinary use and is hardened by alloying with silver, copper, and other metals. These alloys are mostly used in jewellery and coinage.
White gold (an alloy of gold with platinum, palladium, nickel, and/or zinc) serves as a substitute for solid platinum.
Gold is used in restorative dentistry especially in tooth restorations such as crowns and permanent bridges as its slight maliablity makes a superior molar mating surface to other teeth, unlike a harder ceramic crown.


History

Gold has been known and highly valued since prehistoric times. It may have been the first metal used by humans and was valued for ornamentation and rituals. Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt. Egypt and Nubia had the resources to make them major gold-producing areas for much of history. Gold is also mentioned several times in the Old Testament, and is included with the gifts of the magi in the first chapters of Matthew New Testament The south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world’s earliest coinage in Lydia between 643 and 630 BC.
The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, and Colombia.
Although the price of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Gold as a sign of wealth and prestige was made fun of by Thomas More in his treatise Utopia. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly-dressed of their party.
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega. Further gold rushes occurred in California, Colorado, Otago, Australia, Witwatersrand, Black Hills, and Klondike.
Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.

Notes

On the 13th of March 2008 the price of gold reached $1000 per troy ounce (31.1035g) for the first time in history. This works out at $32150 per kilogram!
It is the most malleable and ductile metal known; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet.
Supposedly around half of the world’s supply of gold is stored in the United States Treasury Department’s gold depository in Fort Knox Kentucky, which is considered to be one of the most secure buildings in the world.
Because gold is traded like currencies, it has it’s own ISO currency code, XAU (USD = US dollars, GBP = GB Pounds sterling etc.).
Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910. It has been estimated that all the gold in the world that has ever been refined would form a single cube 20 m (66 ft) on a side (8000 m3).
At the end of 2001, it was estimated that all the gold ever mined totalled only 145,000 tonnes.

Gold Compounds

Auranofin C20H35AuO9PS+
An organogold compound classified by the World Health Organization as an antirheumatic agent.

Aurothioglucose AuSC6H11O5
A derivative of the sugar glucose, it is used to treat rheumatoid arthritis.

Sodium aurothiomalate C4H3AuNaO4S
an organogold compound used for its antirheumatic effects to treat rheumatoid arthritis. In the United Kingdom only this intramuscular injection drug and the orally taken Auranofin are used medically.

Reactions of Gold

Reactions with water
Gold does not react with water, under any circumstances.

Reactions with air
Under normal conditions gold will not react with air.

Reactions with halogens
Gold reacts with chlorine and bromine to form trihalides and with iodine to form a monohalide.
2Au(s) + 3Cl2(g) --> 2AuCl3(s)
2Au(s) + 3Br2(g) --> 2AuBr3(s)
2Au(s) + I2(g) --> 2AuI(s)

Reactions with acids
Gold can be dissolved with a mixture of hydrochloric acid (HCl) and concentrated nitric acid (HNO3), in a ration of 3:1. This combination is known as aqua regia, "royal water".

Reactions with bases
Gold will not react with aqueous bases.

Occurrence of Gold

Economic gold extraction can be achieved from ore grades as little as 0.5g/1000kg (0.5 parts per million, ppm) on average in large easily mined deposits. Typical ore grades in open-pit mines are 1-5 g/1000 kg (1-5 ppm), ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm) on average. Since ore grades of 30g/1000kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
Since the 1880s, South Africa has been the source for a large proportion of the world’s gold supply. Production in 1970 accounted for 79% of the world supply, producing about 1,000 tonnes. However, production in 2005 was just 294 tonnes according to the British Geological Survey. This sharp decline was due to the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.
The city of Johannesburg was built atop the world’s greatest gold finds. Gold fields in the Free State and Gauteng provinces are deep and require the world’s deepest mines. The Second Boer War of 1899-1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
Other major producers are United States, Australia, China and Peru. Mines in South Dakota and Nevada supply two-thirds of gold used in the United States. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.
After initial production, gold is often subsequently refined industrially by the Wohlwill process or the Miller process. Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cuppelation, or refining methods based on the dissolution of gold in aqua regia.
The world’s oceans hold a vast amount of gold, but in very low concentrations (perhaps 1-2 parts per billion). A number of people have claimed to be able to economically recover gold from sea water, but so far they have all been either mistaken or crooks. Reverend Prescott Jernegan ran a gold-from seawater swindle in America in the 1890s. A British fraud ran the same scam in England in the early 1900s.
Fritz Haber (the German inventor of the Haber process) attempted commercial extraction of gold from sea water in an effort to help pay Germany’s reparations following the First World War. Unfortunately, his assessment of the concentration of gold in sea water was unduly high, probably due to sample contamination. The effort produced little gold and cost the German government far more than the commercial value of the gold recovered. No commercially viable mechanism for performing gold extraction from sea water has yet been identified. Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future.
The average gold mining and extraction costs are $238 per troy ounce but these can vary widely depending on mining type and ore quality. In 2001, global mine production amounted to 2,604 tonnes, or 67% of total gold demand in that year. At the end of 2001, it was estimated that all the gold ever mined totalled 145,000 tonnes.

Isotopes of Gold

195Au [116 neutrons]
Abundance: synthetic
Half life: 186.10 days [ Electron Capture ]
Decay Energy: 0.227 MeV
Decays to 195Pt.

196Au [117 neutrons]
Abundance: synthetic
Half life: 6.183 days [ Electron Capture ]
Decay Energy: 1.506 MeV
Decays to 196Pt.
Half life: 6.183 days [ beta- ]
Decay Energy: 0.686 MeV
Decays to 196Hg.

197Au [118 neutrons]
Abundance: 100%
Stable with 118 neutrons

198Au [119 neutrons] Abundance: synthetic
Half life: 2.69517 [ beta- ]
Decay Energy: 1.372 MeV
Decays to 198Hg.

199Au [120 neutrons] Abundance: synthetic
Half life: 3.169 days [ beta- ]
Decay Energy: 0.453 MeV
Decays to 199Hg.

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 09, 2011

Agustus 07, 2011

SYLVITE [ Halides ]

Agustus 07, 2011 0
KCl, potassium Chloride
As a major source of potash and as mineral specimens


Sylvite, also called sylvine, is a major source of potassium or potash used in fertilizer products. So great is the need for potassium that sylvite deposits are considered very valuable economically. As a mineral specimen sylvite does not get much attention. The crystals can be well formed and are often reddish due to inclusions of hematite. However, sylvite is very soluble in water and specimens need to be stored in closed containers because even the moisture in the air can degrade its appearance. Never clean a sylvite specimen with water.
Sylvite is closely related to the more common halite, NaCl, and they share so many properties that identification is sometimes difficult. Sylvite commonly has octahedral faces truncating the corners of the cubic crystals. So does halite, but this characteristic is much more prevalent in sylvite than in halite. Better tests include a taste test in which halite, salt, will taste salty and sylvite tastes bitter. This test is good if you need to distinguish one or two specimens, but what if you are testing hundreds of feet of core samples for beds of sylvite verses halite. A good test in those cases is the knife test in which a knife blade when scratched across the surface of the sample will produce a powder in halite and not in sylvite.

The name sylvite is easily confused with the much more valuable sylvanite. Sylvanite is a silver gold telluride, AuAgTe4 and should never be mistaken for sylvite.

Physical Characteristics

Colour: colourless or white, sometimes tinted red, blue or yellow
Luster: vitreous
Transparency: Crystals are transparent to translucent
Crystal System: isometric; 4/m bar 3 2/m
Crystal Habits: cubes with frequent octahedral faces truncating the corners of the cube, crystals will often have a cavernous appearance from dissolution. More commonly massive and granular
Cleavage: good in three directions forming cubes
Fracture: uneven
Hardness: 2 - 2.5
Specific Gravity: 3.9 - 4.1 (heavier than average for translucent)
Streak: white
Other: Dissolves easily in water, does not powder when the blade of a knife is scratched across its surface and has a bitter taste, not salty like halite
Associated Minerals: include halite, carnallite, kieserite, gypsum, anhydrite and other evaporite minerals
Major Occurrences: include Strassfurt, Germany; Kalush, Russia; New Mexico, Texas and Kern Co., California, USA; Saskatchewan, Canada; France, Mt. Vesuvius, Italy and Spain
Best Indicators: bitter taste, associations and crystal habit


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Rino Safrizal
Jejaring Kimia Updated at: Agustus 07, 2011

CARNALLITE [ Halides ]

Agustus 07, 2011 2
KMgCl3 - 6H2O, Hydrated Potasium magnesium Chloride
As a source of potash and a minor ore of magnesium and as mineral specimens

Carnallite is named for Prussian mining engineer, Rudolph von Carnall. It forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation. Carnallite precipitates with other potassium and magnesium evaporate minerals such as sylvite, kainite, picromerite, polyhalite and kieserite. Massive beds of carnallite are found but crystals are rare. The crystals will unfortunately absorb water from humid air (a process called deliquescence). This process can be eased by storing specimens in sealed dry containers.

Carnallite is an important source of potash, an invaluable fertilizer. Sylvite is the more important source of potash, but carnallite makes a significant contribution. Carnallite’s magnesium output is of much lesser importance world wide but is still Russia’s most significant source. Potassium is actually a common element, but unfortunately it is bound up in insoluble silicate minerals such as potassium feldspars. In order for potassium to be useful as a fertilizer it needs to be in a soluble form and thus soluble potassium salts are the source of choice.

These minerals are not that easy to form because evaporite minerals such as carnallite and sylvite as it turns out are some of the last minerals to evaporate from sea water. Minerals such as calcite, dolomite, gypsum, anhydrite and halite crystallize first in roughly that order. The conditions that must exist in order to have potassium and magnesium salts form involve having sea water contained in a cut off, but not completely isolated basin similar to the Black Sea. However the Black Sea does not form carnallite because it is not located in a warm enough climate as intensive evaporation is needed (this is an evaporite mineral after all). The basin must also not allow the concentrated brine to leave the basin so as to continually increase its salinity. The brine will sink to the bottom of the basin and allow fresher water to enter the basin which brings more magnesium into the basin. This has the effect of prolonging the crystallization of the salts and increasing the salinity of the brine. If evaporation does not progress this way, then the minerals listed above may fill the basin before the potassium salts have a chance to crystallize.

This scenario for potassium and magnesium salt formation is not observable today because current day basins such as the Black Sea, Hudson Bay, Persian Gulf, Red Sea, Baltic Sea or Sea of Japan have either the wrong shape or the wrong climatic conditions. But this was not always the situation in the geologic past as numerous ancient potassium and magnesium salt deposits have been found. Specifically the Permian, Devonian and Carboniferous time periods were excellent times for such basins and they are responsible for most of the worlds evaporite deposits. Most notable potassium and magnesium salt deposits are found in Carlsbad, New Mexico; the Paradox Basin in Colorado and Utah; deposits in Strassfurt, Germany; the Perm Basin, Russia and the Williston Basin in Saskatchewan, Canada.

Carnallite is relatively easy to distinguish from other evaporate minerals. Its taste is bitter and it has no cleavage, unlike halite. Carnallite is extremely light with a specific gravity of only 1.6 and it also shows a violet flame result when it is put in a gas flame due to its potassium content, unlike kieserite and other non-potassium salts.

Physical Characteristics

Colour: white, colourless or yellow; rarely blue. Hematite inclusions may colour specimens reddish
Luster: vitreous to greasy, resinous or dull
Transparency: Crystals are transparent to translucent
Crystal System: orthorhombic; 2/m 2/m 2/m
Crystal Habits: typically granular and massive, sometimes fibrous. Individual crystals are rare, but when seen are pseudo-hexagonal and tabular
Cleavage: absent
Fracture: conchoidal
Hardness: 2.5
Specific Gravity: approx. 1.6 (light even for translucent minerals)
Streak: white
Other: Bitter taste, deliquescent (meaning it can absorb water from the air), fluorescent and can colour a flame violet (due to potassium)
Associated Minerals: include halite, anhydrite, dolomite, gypsum, kainite, kieserite, polyhalite, sylvite and other more rare potassium evaporite minerals
Major Occurrences: include Carlsbad, New Mexico; Western Texas; Colorado and Utah, USA; Strassfurt, Germany; Ural Mountains, Russia; Iran; China; Tunisia; Spain; Mali; Ukraine and Saskatchewan, Canada
Best Indicators: environment of formation, lack of cleavage, associations, density, deliquescence, fracture and taste

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 07, 2011

Agustus 04, 2011

KALOR PENGUAPAN SEBAGAI ENERGI PENGAKTIFAN PENGUAPAN

Agustus 04, 2011 0
Penguapan merupakan salah satu proses perubahan fisik. Penguapan juga dipandang sebagai suatu reaksi di mana yang berperan sebagai zat cair adalah pereaksi sedangkan hasil reaksi adalah uap yang bersangkutan. Kalor penguapan dan perubahan energy penguapan adalah kalor reaksi dan perubahan entalpi yang dibutuhkan atau dilepaskan pada penguapan 1 mol zat dalam fase cair menjadi 1 mol zat dalam fase gas pada titik didihnya.

Contohnya dapat dilihat dari reaksi pemanasan air pada system terbuka berikut ini:
H2O(l) --> H2O(g) ΔH = + 44 kJ
Selanjutnya, karena penguapan dapat dipandang sebagai proses yang hanya terdiri atas satu tahap, maka kalor penguapan dapat dipandang sebagai energy pengaktifan reaksi penguapan. Berdasarkan perumpamaan ini, kalor penguapan dapat diukur dengan cara yang lazim digunakan untuk energy pengaktifan. Pengukuran energy pengaktifan dilakukan dengan mengukur laju reaksi pada berbagai suhu dan dengan menggunakan persamaan Arrhenius berikut:

Log k = log A (E/2,303 RT)

Keterangan : K = tetapan laju reaksi pada suhu konstan T
A = suatu tetapan
E = energy pengaktifan
R = tetapan gas ideal
T = suhu mutlak

Dengan demikian, kalor penguapan dapat diperoleh dengan mengukur laju penguapan pada berbagai suhu dan dengan mengartikan E sebagai kalor penguapan.
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Rino Safrizal
Jejaring Kimia Updated at: Agustus 04, 2011

Agustus 02, 2011

Iodine [I]

Agustus 02, 2011 0

Characteristics

An: 53 N: 74
Am: 126.90447 (3) g/mol
Group No: 17
Group Name: Halogen
Block: p-block Period: 5
State: solid at 298 K
Colour: Violet-dark grey, lustrous
Classification: Non-metallic
Boiling Point: 457.4K (184.3oC)
Melting Point: 386.85K (113.7oC)
Critical temperature: 819K (546oC)
Density: 4.933g/cm3

Discovery Information

Who: Bernard Courtois
When: 1804
Where: France

Name Origin

Greek: iodes (violet). "Iodine" in different languages.

Sources

Occurs on land and in the sea in sodium and potassium compounds. Although the element is actually quite rare, kelp and certain other plants have the ability to concentrate Iodine, which helps introduce the element into the food chain as well as keeping its cost down.


When heated Iodine sublimates (turns from a solid to a gas) into a violet vapour.
Primary producers are Chile (c.66%) and Japan and the USA. Annual production is around 12 thousand tons.

Abundance

Universe: 0.0001 ppm (by weight)
Carbonaceous meteorite: 0.26 ppm
Earth’s Crust: 1.4 ppm
Seawater: Atlantic surface: 4.89 x 10-2 ppm; Atlantic deep: 5.6 x 10-2 ppm; Pacific surface: 4.3 x 10-2 ppm; Pacific deep: 5.8 x 10-2 ppm
Human: 200 ppb by weight; 10 ppb by atoms

Uses

Required in small amounts by humans. Once used as an antiseptic, but no longer due to its poisonous nature. Silver iodide (AgI) is used in photography. Tungsten iodide is used to stabilise the filaments in light bulbs. Iodine-131 is used as a tracer in medicine.

Potassium iodide (KI tablets, or "SSKI" = "Super-Saturated KI" liquid drops) can be given to people in a nuclear disaster area when fission has taken place, to flush out the radioactive iodine-131 fission product. The half-life of iodine-131 is only eight days, so the treatment would need to continue only a couple of weeks. In cases of leakage of certain nuclear materials without fission, or certain types of dirty bomb made with other than radioiodine, this precaution would be of no avail.

Tungsten iodide (WI) is used to stabilize the filaments in light bulbs.

Iodine-123 and iodine-125 are used in medicine as tracers for imaging and evaluating the function of the thyroid.

Iodine-131 is used in medicine for treatment of thyroid cancer and Grave’s disease.

History

Iodine was discovered by Bernard Courtois in 1811. He was born to a manufacturer of saltpeter (a vital part of gunpowder). At the time France was at war, saltpeter, a component of gunpowder, was in great demand. Saltpeter produced from French niter beds required sodium carbonate, which could be isolated from seaweed washed up on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash then washed with water. The remaining waste was destroyed by adding sulfuric acid. One day Courtois added too much sulfuric acid and a cloud of purple vapour rose. Courtois noted that the vapour crystallized on cold surfaces making dark crystals. Courtois suspected that this was a new element but lacked the money to pursue his observations.

However he gave samples to his friends, Charles Bernard Desormes (1777 - 1862) and Nicolas Clement (1779 - 1841), to continue research. He also gave some of the substance to Joseph Louis Gay-Lussac (1778 - 1850), a well-known chemist at that time, and to Andre-Marie Ampere (1775 - 1836). On 29 November 1813, Dersormes and Clement made public Courtois’ discovery. They described the substance to a meeting of the Imperial Institute of France. On December 6, Gay-Lussac announced that the new substance was either an element or a compound of oxygen
. Ampere had given some of his sample to Humphry Davy (1778 - 1829). Davy did some experiments on the substance and noted its similarity to chlorine. Davy sent a letter dated December 10 to the Royal Society of London stating that he had identified a new element. A large argument erupted between Davy and Gay-Lussac over who identified http://jejaringkimia.blogspot.com/2011/08/iodine-i.html first but both scientists acknowledged Bernard Courtois as the first to isolate the chemical element.

Notes

It is an essential trace element; the thyroid hormones, thyroxine and triiodothyronine contain Iodine.
Iodine is a dark-gray/purple-black solid that sublimes at standard temperatures into a purple-pink gas that has an irritating odour. This halogen forms compounds with many elements, but is less active than the other members of the halogens and has some metallic-like properties.

Hazards

Toxic, many be fatal is swallowed or inhaled. Direct contact with skin can cause lesions, so it should be handled with care. Iodine vapour is very irritating to the eye and to mucous membranes.
When mixed with ammonia (NH3) it can form nitrogen triiodide (NI3) which is extremely sensitive and can explode unexpectedly.

Iodine Compounds

Ammonium iodide NH4I
It is used in photographic chemicals and some medications.

Iodic acid HIO3
Iodic acid is used as a standard strong acid in analytical chemistry. It may be used to standardize solutions of both weak and strong bases, with methyl red or methyl orange as the indicator.

Lead(II) iodide PbI2 [ Toxic ]
As toxic, yellowish solid. In its crystalline form it is used as a detector material for high energy photons including x-rays and gamma rays.

Lithium iodide LiI
Lithium iodide is used as an electrolyte for high temperature batteries. It is also used for long life batteries as required, for example, by cardiac pacemakers. The solid is used as a phosphor for neutron detection.

Nitrogen triiodide NI3
Also called nitrogen iodide, is a highly explosive compound of nitrogen and Iodine
. It is a contact explosive, and small quantities explode with a gunpowder-like snap when touched by even a feather, releasing a volatile cloud of Iodine vapour.
Small amounts of nitrogen triiodide are sometimes synthesized as a demonstration to chemistry students. However, because the compound is so unstable, it has not been used in blasting caps or primers for explosives.
The reason for it’s instability is due to the size difference between the two different types of atoms. The three Iodine atoms are much bigger than the nitrogen atom holding them together. Because of this, not only is the bond between nuclei under much stress and therefore weaker, but the outside electrons of the different iodine atoms are very close, which increases the overall instability of the molecule.

Potassium iodide KI
Potassium iodide is used in photography, in the preparation of silver(I) iodide for high speed photographic film.

Potassium iodide may also be used to protect the thyroid from radioactive iodide in the event of an accident or terrorist attack at a nuclear power plant, or other nuclear attack, especially where a nuclear reactor is breached and the volatile radionuclides, which contain significant amount of 131I, are released into the environment. Radioiodine is a particularly dangerous radionuclide because the body concentrates it in the thyroid gland.

Sodium iodide NaI
Sodium iodide is commonly used to treat and prevent iodine deficiency. Solid crystals can be used to detect radiation (e.g. radiation from uranium) - a solid crystal of sodium iodide creates a pulse of light when radiation interacts with it.

Thyroxine (T4) 3,5,3’,5’-tetra-iodothyronine
An important hormone produced by the thyroid gland.
The thyroid hormones are essential to proper development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds. Numerous physiological and pathological stimuli influence thyroid hormone synthesis.
Hypothyroidism is a disorder where there is a deficiency of thyroxine. Thyrotoxicosis or hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine, free triiodothyronine, or both.

Triiodothyronine (T3)
An important hormone produced by the thyroid gland.

The thyroid hormones are essential to proper development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds. Numerous physiological and pathological stimuli influence thyroid hormone synthesis.
Hypothyroidism is a disorder where there is a deficiency of thyroxine. Thyrotoxicosis or hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine, free triiodothyronine, or both.

Reactions of Iodine

Reactions with water
Iodine reacts with water to produce hypoiolite, OI-. The pH of the solution determines the position of the equilibrium.
I2(l) + H2O(l) --> OI-(aq) + 2H+(aq) + I-(aq)
 
Reactions with air
Iodine is not reactive towards with oxygen
or nitrogen
. However, iodine does react with ozone, O3 to form the unstable yellow I4O9.
Reactions with halogens
Iodine reacts with fluorine at room temperature to form the iodine(V) pentafluoride. At 250oC the same reaction yields iodine(VII) heptafluoride. With careful control of the reaction conditions, (-45oC, suspension of CFCl3), it is posible to isolate the iodine(III) fluoride.
I2(s) + 5F2(g) --> 2IF5(l)
I2(s) + 7F2(g) --> 2IF7(g)
I2(s) + 3F2(g) --> 2IF3(s)
Iodine reacts with bromine to form the very unstable interhalogen species iodine(I) bromide.
I2(s) + Br2(l) --> 2IBr(s)
Iodine reacts with chlorine at -80oC with excess liquid chlorine to form iodine (III) chloride.
I2(s) + 3Cl2(l) --> I2Cl6(s)
Iodine reacts with chlorine in the presence of water to form iodic acid.
I2(s) + 6H2O(l) + 5Cl2(g) --> 2HIO3(s) + 10HCl(g)
 
Reactions with acids
Iodine reacts with hot concentrated nitric acid to form iodic acid. The iodic acid crystallizes out on cooling.
3I2(s) + 10HNO3(aq) --> 6HIO3(s) + 10NO(g) + 2H2O(l)
 
Reactions with bases
Iodine reacts with hot aqueous alkali to produce iodate, IO3-. Only one sixth of the total iodine is converted in this reaction.
3I2(g) + 6OH-(aq) --> IO3-(aq) + 5I-(aq) + 3H2O(l)

Occurrence of Iodine

Iodine naturally occurs in the environment chiefly as dissolved iodide in seawater, although it is also found in some minerals and soils. The element may be prepared in an ultrapure form through the reaction of potassium iodide with copper(II) sulfate. There are also a few other methods of isolating this element. Although the element is actually quite rare, kelp and certain other plants have the ability to concentrate iodine, which helps introduce the element into the food chain as well as keeping its cost down. 

Iodine is found in the mineral Caliche, found in Chile, between the Andes and the sea. It can also be found in some seaweeds as well as extracted from seawater, however extracting Iodine from the mineral is the only economical way to extract the substance. 

Extraction from seawater involves electrolysis, the brine is first purified and acidified using sulphuric acid and is then reacted with chlorine. An Iodine solution is produced but it is yet too dilute and has to be concentrated. To do this air is blown into the solution which causes the iodine to evaporate, then it is passed into an absorbing tower containing acid where sulfur dioxide (SO2) is added to reduce the iodine, the solution is then added to chlorine again to concentrate the solution more, the final solution is the Iodine at a level of about 99%. 

Another source is from kelp. This source was used in the 18th and 19th centuries but is no longer economically viable. 

In 2005, Chile was the top producer of iodine with almost two-thirds world share followed by Japan and the USA reports the British Geological Survey.

Isotopes of Iodine

There are 37 isotopes of iodine and only one, I-127, is stable.
Iodine-123 and iodine-125 are used in medicine as tracers for imaging and evaluating the function of the thyroid. 

127I [74 neutrons]
Abundance: 100%
Stable with 74 neutrons 

129I [76 neutrons]
Abundance: synthetic
Half life: 1.57 x 107 years [ beta- ]
Decay Energy: 0.194 MeV
Decays to 129Xe.
Excesses of stable 129Xe in meteorites have been shown to result from decay of "primordial" iodine-129 produced newly by the supernovas which created the dust and gas from which the solar system formed.
129I (half-llife 15.7 million years) is a product of cosmic ray spallation on various isotopes of xenon in the atmosphere, in cosmic ray muon interaction with tellurium-130, and also uranium
and plutonium fission, both in subsurface rocks and nuclear reactors. Nuclear processes, in particular nuclear fuel reprocessing and atmospheric nuclear weapons tests have now swamped the natural signal for this isotope. 129I was used in rainwater studies following the Chernobyl accident. It also has been used as a groundwater tracer and as an indicator of nuclear waste dispersion into the natural environment. 

131I (radioiodine) [78 neutrons]
Abundance: synthetic
Half life: 8.02070 days [ beta- ]
Decay Energy: 0.971 MeV
Decays to 131Xe.
Has been used in treating cancer and other pathologies of the thyroid gland.

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 02, 2011

Helium [He]

Agustus 02, 2011 2

Characteristics

An: 2 N: 2
Am: 4.002602 g/mol
Group No: 18
Group Name: Noble gas
Block: p-block Period: 1
State: gas at 298 K
Colour: colourless
Classification: Non-metallic
Boiling Point: 4.22K (-268.93oC)
Melting Point: 0.95K (-272.2oC) @ 2.5MPa
Critical temperature: 5.19K (-267.96oC)
Density: 0.1786g/l

Availability:

There is very little helium on earth as nearly all present during and immediately after the earth’s formation has long since been lost as it is so light. Just about all the helium remaining on the planet is the result of radioactive decay. While there is some helium in the atmosphere, currently its isolation from that source by liquefaction and separation of air is not normally economic. This is because it is easier, and cheaper, to isolate the gas from certain natural gases. Concentrations of helium in natural gas in the USA are as high as 7% and other good sources include natural gas from some sources in Poland. It is isolable from these gases by liquefaction and separation of from the natural gas. This would not normally be carried out in the laboratory and helium is available commercially in cylinders under pressure.

Discovery Information

Who: Sir William Ramsey, Nils Langet, P T Cleve
When: 1895
Where: Scotland/Sweden

Name Origin

Greek: helios (sun). "helium" in different languages.

Sources

Found in natural gas deposits and in the air (5 parts per billion) Constantly lost to space; replenished by radioactive decay (alpha particles). helium is the second most abundant element in the universe by mass (25%). Most of the helium supplied around the world comes from the area around Amarillo, Texas.
Annual commercial production is around 4500 tons.

Abundance

Universe: 2.3 x 105 ppm (by weight)
Sun: 2.3 x 105 ppm (by weight)
Atmosphere: 5.2 ppm
Earth’s Crust: 0.008 ppm
Seawater: 7 x 10-6 ppm

Uses

Used in balloons as it is lighter than air, and unlike hydrogen, not flammable; deep sea diving and welding. Also used in very low temperature research and nuclear power plant coolant. Future possible uses include use as coolant for nuclear fusion power plants and in superconducting electric systems.

At extremely low temperatures, liquid helium is used to cool certain metals to produce superconductivity, such as in superconducting magnets used in magnetic resonance imaging. Helium at low temperatures is also used in cryogenics.

Because it is inert, helium is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, in gas chromatography, and as an atmosphere for protecting historical documents. This property also makes it useful in supersonic wind tunnels.

History

Evidence of helium was first detected on August 18, 1868 as a bright yellow line with a wavelength of 587.49 nanometres in the spectrum of the chromosphere of the Sun, by French astronomer Pierre Janssen during a total solar eclipse in Guntur, India. This line was initially assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D3 line, for it was near the known D1 and D2 lines of sodium, and concluded that it was caused by an element in the Sun unknown on Earth. He and English chemist Edward Frankland named the element with the Greek word for the Sun.

On 26 March 1895 British chemist William Ramsay isolated helium on Earth by treating the mineral cleveite with mineral acids. Ramsay was looking for argon but, after separating nitrogen and oxygen from the gas liberated by sulfuric acid, noticed a bright-yellow line that matched the D3 line observed in the spectrum of the Sun. These samples were identified as hhelium by Lockyer and British physicist William Crookes. It was independently isolated from cleveite the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight. helium was also isolated by the American geochemist William Francis Hillebrand prior to Ramsay’s discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen. His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science.

In 1907, Ernest Rutherford and Thomas Royds demonstrated that an alpha particle is a helium nucleus. In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin. He tried to solidify it by further reducing the temperature but failed because helium does not have a triple point temperature where the solid, liquid, and gas phases are at equilibrium. It was first solidified in 1926 by his student Willem Hendrik Keesom by subjecting helium to 25 atmospheres of pressure.

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no viscosity at temperatures near absolute zero, a phenomenon now called superfluidity. In 1972, the same phenomenon was observed in helium-3 by American physicists Douglas D. Osheroff, David M. Lee, and Robert C. Richardson.

Notes

helium has the lowest melting and boiling point of any element. Liquid Helium is called a "quantum fluid" as it displays atomic properties on a macroscopic scale. The viscosity of liquid helium is 25 micropoises (water has a viscosity of 10,000 micropoises). As helium is cooled below its transition point, it has an unusual property of superfluidity with a viscosity approaching zero micropoises. In addition, liquid helium has extremely high thermal conductivity.

helium is the second most abundant and second lightest element in the periodic table. It is also the least reactive of all the group 18 (noble gases) elements.

One cubic metre of helium will lift 1kg. helium is the preferred choice for airships as although it is more expensive it is not flammable and has 92% the lifting power of hydrogen.

The voice of a person who has inhaled helium temporarily sounds high-pitched, resembling those of the cartoon characters "Alvin and the Chipmunks". This is because the speed of sound in helium is nearly three times that in air. Although the vocal effect of inhaling helium may be amusing, it can be dangerous if done to excess since helium is a simple asphyxiant, thus it displaces oxygen needed for normal respiration. Death by asphyxiation will result within minutes if pure helium is breathed continuously.

Helium Compounds

helium is chemically unreactive under all normal conditions due to its valence of zero. Because of this extreme conditions are needed to create the small handful of helium compounds, which are all unstable at standard temperature and pressure.

No useful (with exception to those produced for scientific research) or commercial helium compounds exist.

Reactions of Helium

Helium is chemically unreactive under all normal conditions due to its valence of zero. It is an electrical insulator unless ionized. As with the other noble gases, helium has metastable energy levels that allow it to remain ionized in an electrical discharge with a voltage below its ionization potential. Helium can form unstable compounds with tungsten, iodine, fluorine, sulfur and phosphorus when it is subjected to an electric glow discharge, through electron bombardment or is otherwise a plasma. HeNe, HgHe10, WHe2 and the molecular ions He2+, He2++, HeH+, and HeD+ have been created this way. This technique has also allowed the production of the neutral molecule He2, which has a large number of band systems, and HgHe, which is apparently only held together by polarization forces. Theoretically, other compounds, like helium fluorohydride (HHeF), may also be possible.

Occurrence and Production of Helium

Natural Abundance
helium is the second most abundant element in the known Universe after hydrogen and constitutes 23% of the elemental mass of the universe. It is concentrated in stars, where it is formed from hydrogen by the nuclear fusion of the proton-proton chain reaction and CNO cycle. According to the Big Bang model of the early development of the universe, the vast majority of helium was formed during Big Bang nucleosynthesis, from one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models.

In the Earth’s atmosphere, the concentration of helium by volume is only 5.2 parts per million, largely because most helium in the Earth’s atmosphere escapes into space due to its inertness and low mass. In the Earth’s heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements.
Nearly all helium on Earth is a result of radioactive decay. The decay product is primarily found in minerals of uranium and thorium, including cleveites, pitchblende, carnotite, monazite and beryl, because they emit alpha particles, which consist of helium nuclei (He2+) to which electrons readily combine. In this way an estimated 3.4 litres of helium per year are generated per cubic kilometer of the Earth’s crust. In the Earth’s crust, the concentration of helium is 8 parts per billion. In seawater, the concentration is only 4 parts per trillion. There are also small amounts in mineral springs, volcanic gas, and meteoric iron. The greatest concentrations on the planet are in natural gas, from which most commercial helium is derived.

Modern Extraction
For large-scale use, helium is extracted by fractional distillation from natural gas, which contains up to 7% helium. Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and methane). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure, Grade-A, helium. The principal impurity in Grade-A helium is neon.

As of 2004, over one hundred and fifty million cubic metres of helium were extracted from natural gas or withdrawn from helium reserves, annually, with approximately 84% of production from the United States, 10% from Algeria, and most of the remainder from Canada, China, Poland, Qatar, and Russia. In the United States, most helium is produced in Kansas and Texas.

Diffusion of crude natural gas through special semi-permeable membranes and other barriers is another method to recover and purify helium. Helium can be synthesized by bombardment of lithium or boron with high-velocity protons, but this is not an economically viable method of production.

Isotopes of Helium

A subset of exotic light nuclei, the exotic helium isotopes have larger atomic masses than helium’s natural isotopes. Although all exotic helium isotopes decay with a half-llife of less than one second, researchers have eagerly created exotic light isotopes through particle accelerator collisions to create unusual atomic nuclei for elements such as helium, lithium, and nitrogen. The bizarre nuclear structures of such isotopes may offer insight into the isolated properties of neutrons.

The most widely-studied exotic helium isotope, for example, is helium-8. This isotope is thought to consist of a normal helium-4 nucleus surrounded by four neutrons dubbed a "halo" (6He also has a halo of neutrons). Halo nuclei have become an area of intense research. isotopes up to helium-10, with two protons and eight neutrons, have been confirmed. By comparison, the most common He-4 isotope has only two neutrons.
There are eight known isotopes of helium, but only helium-3 and helium-4 are stable. In the Earth’s atmosphere, there is one He-3 atom for every million He-4 atoms.

The most common isotope, helium-4, is produced on Earth by alpha decay of heavier radioactive elements; the alpha particles that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its nucleons are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis.

3He [1 neutrons]
Abundance: 0.000137%
Stable with 1 neutron
Extraplanetary material, such as lunar and asteroid regolith, have trace amounts of helium-3 from being bombarded by solar winds. The Moon’s surface contains helium-3 at concentrations on the order of 0.01 ppm.


4He [2 neutrons]
Abundance: 99.999863%
Stable with 2 neutrons
Liquid helium-4 can be cooled to about 1 kelvin using evaporative cooling.

5He [3 neutrons]
Abundance:
Half life: 7.00(30) x 10-24 seconds
Decays to 4He.
Highly unstable, decays to 4He.

6He [4 neutrons]
Abundance:
Half life: 806.7(15) ms [ beta- ]
Decays to 6Li.
Produced from 7He or 11Li.
7He [5 neutrons]
Abundance:
Half life: 2.9(5)-21 seconds
Highly unstable, decays to 6He.
8He [6 neutrons]
Abundance:
Half life: 119.0(15) ms
Produced from 9He, decomposes to 7Li through beta decay then emits a delayed neutron.

9He [7 neutrons]
Abundance:
Half life: 7(4) x 10-21 seconds
Highly unstable, decays to 8He.

10He [8 neutrons]
Abundance:
Half life: 2.7(18) x 10-21 seconds
Highly unstable, decays to 9He.

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Rino Safrizal
Jejaring Kimia Updated at: Agustus 02, 2011

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