ANALISA KUALITATIF PROTEIN PADA BEBERAPA BAHAN MAKANAN

ANALISA KUALITATIF PROTEIN PADA BEBERAPA BAHAN MAKANAN

Protein merupakan komponen utama semua sel hidup. Protein berfungsi sebagai pembentuk stuktur sel yang menghasilkan hormon, enzim, dll.

Protein dapat diklasifikasikan berdasarkan kelarutannya yaitu protein fibrosa dan protein globular. Protein fibrosa merupakan protein yang tidak larut dalam air. Termasuk dalam golongan ini adalah :
  1. kolagen : terdapat dalam tulang, gigi, dan kulit
  2. keratin : terdapat dalam rambut, kuku, wool
  3. myosin : di jumpai pada otot-otot yang berkontraksi
  4. elastin : pada kulit
Untuk protein globular merupakan protein yang larut dalam air atau air yang mengandung garam-garam tertentu. Yang termasuk golongan ini adalah albumin, globulin, insulin, dan protein enzim. Apabila dilihat dari unsur penyusunnya protein dibagi ke dalam golongan protein sederhana dan protein majemuk. Dikatakan protein sederhana apabila hasil hidrolisis sempurna protein akan menghasilkan hanya alfa asam amino. Dari golongan termasuk diantaranya albumin dan globulin. Untuk protein majemuk adalah protein yang mengandung gugus non protein di dalamnya seperti gugus gula, lipida, logam-logam, asam inti dan ester fosfat. Protein golongan ini meliputi lipoprotein (membawa lipida), Glikoprotein (membawa glukosa), nucleoprotein (membawa asam inti seperti ribose), dan fosfoprotein (membawa gugus ester fosfat seperti kasein).

Pada umunya protein mempunyai sifat sebagai senyawa amorf, tidak berwarna, mempunyai titik leleh dan titik didih yang tidak tetap, tak larut dalam pelarut organik dan apabila dilarutkan dalam air membentuk suatu larutan koloid. Protein ini mudah rusak karena pengaruh panas, penambahan logam, dan pengaruh asam atau basa.

Protein dapat ditemukan dalam beberapa bahan makan. Untuk dapat menentukan kandungan protein dalam bahan makanan secara teliti merupakan pekerjaan yang tidak mudah. Hal ini disebabkan protein mempunyai struktur yang kompleks dengan beragam komposisi dan sifat yang sangat sulit dipisahkan, dimurnikan dan dikeringkan. Sifat amfotir dan hidrasi menyebabkan komposisi protein tergantung pada pH, suhu dan pelarut. Pada umumnya protein dengan mudah diendapkan dari larutannya. Namun, hal ini tidak berarti proses isolasi protein dalam bahan makan sangat sederhana seperti mengendapkan, menyaring, mengeringkan dan menimbang. Permasalahan yang dihadapi tidak adanya pereaksi yang dapat mengendapkan protein dengan selektif. Lipida, garam, dan beberapa molekul yang lain yang terdapat dalam bahan makan akan ikut terendapkan bersama dengan protein. Beberapa senyawa di atas dapat dengan mudah dipisahkan dengan protein melalui pencucian dengan air tetapi untuk mendapatkan protein yang kering sangat sulit mengingat tingkat hidrasi dari protein sangat tinggi. Sekalipun proses hidrasi bersifat reversible tetapi pada pemanasan yang lama dapat menyebabkan kerusakan protein.

SIFAT PROTEIN

Karena protein tersusun oleh asam-asam amino, maka protein mempunyai sifat mirip dengan asam-asam amino. Protein merupakan suatu koloid elektrolit yang bersifat amfotir. Dengan sifat ini protein dapat bersifat asam maupun basa. Sifat amfotir ini, tergantung jumlah gugus NH2 dari amina dan COOH dari asam. Dalam bentuk netral senyawa ini berbentuk dua kutub ion (zwizter ion). Pada keadaan dua kutub ion ini, disebut titik isoelektrik.

Pada keadaan titik isoelektrik ini jumlah muatan positif dan negative sama. Dengan menambahlan asam (menurunkan pH di bawah titik isoelektrik) membuat sifat proteinbertindak sebagai basa, sedangkan pada penambahan basa, protein menjadi asam. Titik isoelektrik ini berguna untuk memisahkan asam-asam amino penyusun protein karena setiap asam amino mempunyai titik isoelektrik (pI) yang berlainan. Sebagai contoh pada pH di atas isoelektrik protein berada dalam bentuk ion negative mampu bereaksi dengan suatu kation sedang pada pH di bawah titik isoelektrik (berbentuk muatan positif) protein mampu mengikat ion.

Adanya berbagai gugus fungsional (NH2, NH, OH, CO) dan bentuk ion ganda (switzer ion) yang terdapat dalam struktur protein dapat menyebabkan terjadinya reaksi pengendapan protein. Gugus fungsional tersebut mampu mengikat molekul air melalui pembentukan ikatan hydrogen. Reaksi pengendapan dapat terjadi karena penambahan bahan-bahan kimia seperti garam-garam dan pelarut organic yang dapat merubah sifat kelarutan protein dalam air.

Bahan Rujukan

Anwar, Chairil. 1996. Pengantar Praktikum Kimia Organik. Yogyakarta : Depdikbud
Lehninger, Albert. 1995. Dasar-Dasar Biokimia Jilid I. Jakarta : Erlangga
ADSORPSI PADA LARUTAN

ADSORPSI PADA LARUTAN

Adsorpsi adalah suatu peristiwa penyerapan pada permukaan adsorbe. Misalnya zat padat akan menarik molekul-molekul gas atau zat cair pada permukaannya. Hal ini disebabkan karena zat padat yang terdiri dari molekul-molekul tarik menarik dengan gaya Van der Waals. Jika ditinjau satu molekul, maka molekul ini akan dikelilingi molekul lain yang mempunyai gaya tarik yang seimbang. Untuk molekul, gaya tari dipermukaannya tidak seimbang karena salah satu arah tidak ada molekul lain yang menarik, akibatnya pada permukaan itu akan mempunyai gaya tarik kecil. Adsorpsi dipengaruhi oleh macam zat yang diadsorpsi, konsentrasi adsorben dan zat yang diadsorpsi, luas permukaan, suhu, dan tekanan.

Untuk adsorben yang permukaannya besar, maka adsorpsinya juga semakin besar. Makin besar konsentrasi, makin banyak zat yang diadsorpsi. Sifat adsorpsi pada permukaan zat padat adalah selektif, artinya pada campuran zat hanya satu komponen yang diadsorpsi oleh zat tersebut.
Pengaruh konsentrasi larutan terhadap adsorpsi dapat dinyatakan sebagai berikut:


X/m = k C1/n
Untuk:
X = berat zat yang diadsorspsi
m = berat adsorben
C = konsentrasi zat yang diadsorpsi
n dan k adalah tetapan,
Jika ditulis dalam bentuk logaritma menjadi :
Log (X/m) = n log C – log k
Untuk menentukan n dan k dengan membuat grafik log (X/m) versus log C. sebagai garis lurus, slopenya adalah n dan intersepnya adalah log k, sehingga harga k dapat ditentukan. Menurut persamaan Langmuir (adsorpsi Isoterm Langmuir) dengan notasi sama, hanya bentuk tetapannya yang berbeda.

Manganese [Mn]

Characteristics

An: 25 N: 30
Am: 54.938049 g/mol
Group No: 7
Group Name: Transition metals
Block: d-block Period: 4
State: solid at 298 K
Colour: silvery metallic Classification: Metallic
Boiling Point: 2234K (2061oC)
Melting Point: 1519K (1246oC)
Density: 7.21g/cm3

Discovery Information

Who: Johann Gahn
When: 1774
Where: Sweden

Name Origin

Latin: mangnes (magnet); Ital. manganese. "Manganese" in different languages.

Sources

Most abundant ores are pyrolusite (MnO2), braunite (Mn2+Mn3+6SiO12), psilomelane [(BaH2O)2Mn5O10] and rhodochrosite (MnCO3). Manganese is mined in South Africa, Russia, Ukraine, Georgia, Gabon and Australia. Vast quantities of manganese exist in manganese nodules on the ocean floor. Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.
Psilomelane is one of the most abundant manganese ores.

Pyrolusite is one of the most abundant manganese ores.
Annual production is around 6.2 million tons.

Abundance

Universe: 8 ppm (by weight)
Sun: 10 ppm (by weight)
Carbonaceous meteorite: 2800 ppm
Earth’s Crust: 1100 ppm
Seawater: Atlantic surface: 1 x 10-4 ppm; Atlantic deep: 9.6 x 10-5 ppm; Pacific surface: 1 x 10-4 ppm; Pacific deep: 4 x 10-5 ppm
Human: 200 ppb by weight; 23 ppb by atoms

Uses

Manganese is essential to iron and steel production, it also used in some aluminium alloys. It is also used in making; batteries, axles, rail switches, safes, ploughs and ceramics.
Manganese is used to decolourize glass (removing the greenish tinge that presence of iron produces) and, in higher concentration, make violet-coloured glass.
Potassium permanganate (KMnO4) is a potent oxidizer and used in chemistry and in medicine as a disinfectant.

History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece were both called magnes, but were thought to differ in gender. The male magnes attracted iron, and was the iron ore we now know as loadstone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolourize glass. This feminine magnes was later called magnesia, known now in modern times as Pyrolusite (MnO2) or manganese dioxide. This mineral is never magnetic (although manganese itself is paramagnetic). In the 16th century, it was called manganesum by glassmakers, possibly as a corruption of two words since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Mercati called magnesia negra Manganesa, and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated,much later.
Manganese compounds were in use in prehistoric times; paints that were pigmented with manganese dioxide can be traced back 17,000 years. The Egyptians and Romans used manganese compounds in glass-making, to either remove colour from glass or add colour to it. Manganese can be found in the iron ores used by the Spartans. Some speculate that the exceptional hardness of Spartan steels derives from the inadvertent production of an iron-manganese alloy.
In the 17th century, German chemist Johann Glauber first produced permanganate, a useful laboratory reagent (although some people believe that it was discovered by Ignites Kaim in 1770). By the mid-18th century, manganese dioxide was in use in the manufacture of chlorine (which it produces when mixed with hydrochloric acid (HCl), or commercially with a mixture of dilute sulfuric acid and sodium chloride). The Swedish chemist Scheele was the first to recognize that manganese was an element, and his colleague, Johan Gottlieb Gahn, isolated the pure element in 1774 by reduction of the dioxide with carbon. Around the beginning of the 19th century, scientists began exploring the use of manganese in steelmaking, with patents being granted for its use at the time. In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle. In 1837, British academic James Couper noted an association between heavy exposure to manganese in mines with a form of Parkinson’s Disease. In 1912, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.
In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (carbon-zinc) and alkaline type.

Notes

More than 25 million tonnes of manganese ores are mined every year, representing 5 million tons of the metal, reserves of manganese are estimated to exceed 3 billion tonnes.

Hazards

Manganese is one out of three toxic essential trace elements, which means that it is not only necessary for humans to survive, but it is also toxic when too high concentrations are present in a human body. When people do not live up to the recommended daily allowances their health will decrease. But when the uptake is too high health problems will also occur.

Manganese Compounds

Manganese(II) carbonate MnCO3
It is widely used as an additive to plant fertilizers to cure manganese deficient crops. It is also used in many health foods. It is also used in ceramics as a glaze colourant and flux.
Manganese(IV) oxide MnO2
The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery.

Reactions of Manganese

Reactions with water
Manganese does not react with water under normal conditions
Reactions with air
When finely divided, manganese metal burns in air. It burns in oxygen to form the oxide Mn3O4 and in nitrogen to form the nitride Mn3N2.
3Mn(s) + 2O2(g) --> Mn3O4(s)
3Mn(s) + N2(g) --> Mn3N2(s)

Reactions with halogens
Manganese burns in chlorine to form manganese(II) chloride.
Mn(s) + Cl2(g) --> MnCl2(s)
Manganese burns in bromine to form manganese(II) bromide.
Mn(s) + Br2(g) --> MnBr2(s)
Manganese burns in iodine to form manganese(II) iodide.
Mn(s) + I2(g) --> MnI2(s)

The corresponding reaction between the metal and fluorine yields the manganese(II) fluoride and manganese(III) fluoride.
Mn(s) + F2(g) --> MnF2(s)
2Mn(s) + 3F2(g) --> 2MnF3(s)

Reactions with acids
Manganese metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Mn(II) ion together with hydrogen gas.
Mn(s) + H2SO4(aq) --> Mn2+(aq) + SO42-(aq) + H2(g)

Occurrence of Manganese

Manganese occurs principally as Pyrolusite (MnO2), and to a lesser extent as rhodochrosite (MnCO3). Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. Over 80% of the known world manganese resources are found in South Africa and Ukraine. Other important manganese deposits are in China, Australia, Brazil, Gabon, India, and Mexico. US Import Sources (1998-2001): Manganese ore: Gabon, 70%; South Africa, 10%; Australia, 9%; Mexico, 5%; and other, 6%. Ferromanganese: South Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%. Manganese contained in all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico, 8%; and other, 27%.
Vast quantities of manganese exist in manganese nodules on the ocean floor. Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s. Manganese is mined in Burkina Faso and Gabon.

Isotopes of Manganese

52Mn [27 neutrons]
Abundance: Synthetic
Half life: 5.591 days [ Electron Capture ]
Decay Energy: ? MeV
Decays to 52Cr.
Half life: 5.591 days [ beta+ ]
Decay Energy: 0.575 MeV
Decays to 52Cr.
Half life: 5.591 days [ Gamma Radiation ]
Decay Energy: 0.7, 0.9, 1.4 MeV
Decays to ?. 

53Mn [28 neutrons]
Abundance: Synthetic
Half life: 3.74 x 106 years [ Electron Capture ]
Decay Energy: ? MeV
Decays to 53Cr.
54Mn [29 neutrons]
Abundance: Synthetic
Half life: 312.3 days [ Electron Capture ]
Decay Energy: ? MeV
Decays to 54Cr.
Half life: 312.3 days [ Gamma Radiation ]
Decay Energy: 0.834 MeV
Decays to ?. 

55Mn [30 neutrons]
Abundance: 100%
Stable with 30 neutrons





PEMBUATAN KALIUM SULFIT

Sulfur dioksida dengan mudah larut dalam air menghasilkan larutan asam sulfit (H2SO3). Asam tidak dapat diisolasi dalam bentuk anhidrat.
H2O + SO2 --> H2SO3
Ionisasi asam dapat dilakukan dalam air melalui 2 tahap :
H2SO3  --> H+ + HSO3- K1 = 1,2 . 10-3
HSO3-  --> H+ SO3- K2 = 6,2 . 10-3
Ketika SO2 bergelembung melalui cairan NaOH dihasilkan natrium bisulfat (NaHSO3). Asam garam ini dapat dinetralisasi dengan penambahan NaOH atau Na2CO3 untuk menghasilkan natrium sulfit.
NaOH + H2SO3 → NaHSO3 + H2O
NaOH + NaHSO3 →Na2SO3 + H2O
Ion sulfit dapat berbentuk piramida dan mempunyai geometri electron berbentuk tetrahedral, yang dapat digambarkan sebagai berikut :

Banyak asam oksida termasuk SO2 mempunyai kelarutan lemah dalam air. Meskipun mereka larut dalam larutan hidroksida membentuk garam-garam dari axianionnya.
Reaksinya :
SO2(g) + KOH(aq) → KH3O3(aq)
Atau
SO2(g) + 2KOH(aq) → K2SO3(aq) + H2O(l)
Natrium sulfit jika direaksikan dengan garam kalium klorida akan menghasilkan kalium sulfit, dan garam natrium klorida. Reaksinya sebagai berikut :
Na2SO3(s) + 2KCl(s) → K2SO3(s) + 2NaCl(s)

Sulfur [S]

Characteristics

An: 16 N: 16
Am: 32.065 g/mol
Group No: 16
Group Name: Chalcogen
Block: p-block Period: 3
State: solid at 298 K
Colour: lemon yellow Classification: Non-metallic
Boiling Point: 717.87K (444.72oC)
Melting Point: 388.36K (115.21oC)
Critical temperature: 1314K (1041oC)
Density: (alpha) 2.08g/cm3
Density: (beta) 1.96g/cm3
Density: (gamma) 1.92g/cm3

Discovery Information

Who: Known to the ancients. Homer mentioned "pest-averting sulfur" in the 8th century BC.

Name Origin

Latin: sulfur (brimstone). "Sulfur" in different languages.

Sources

Found in pure form (near hot springs and in volcanic regions) and in ores like cinnabar (HgS), galena (PbS), alunite, barite (BaSO4), sphalerite (ZnS) and stibnite (Sb2S3).
sulfur is a component of many of the complex organic compounds that are found in crude oil. It also occurs as hydrogen sulfide in natural gas. This piece of sulfur came from a natural gas plant near Tioga, North Dakota (USA).
Primary producers are the USA and Spain. Around 54 million tons are produced annually.

Abundance

Universe: 500 ppm (by weight)
Sun: 400 ppm (by weight)
Carbonaceous meteorite: 41000 ppm
Earth’s Crust: 420 ppm
Seawater: 928 ppm
Human: 2 x 106 ppb by weight; 3.9 x 105 ppb by atoms

Uses

Used in matches, gunpowder, detergents, fireworks, batteries, fungicides, vulcanization of rubber, medicines, permanent wave lotion and pesticides. Its most important use is probably that of sulfuric acid (H2SO4). Sulfites are used to bleach paper and as a preservative in wine and dried fruit. Sodium or ammonium thiosulfate are used as photographic fixing agents. Magnesium sulfate, better known as Epsom salts, can be used as a laxative, a bath additive, an exfoliant, or a magnesium supplement for plants.

History

Homer mentioned "pest-averting sulfur" in the 8th century BC and in 424 BC, the tribe of Boeotia destroyed the walls of a city by burning a mixture of coal, sulfur, and tar under them.
sulfur was known in China since the 6th century BC, in a natural form that the Chinese had called ’brimstone’, or shiliuhuang that was found in Hanzhong. By the 3rd century, the Chinese discovered that sulfur could be extracted from pyrite. Chinese Daoists were interested in sulfur’s flammability and its reactivity with certain metals, yet its earliest practical uses were found in traditional Chinese medicine. A Song Dynasty military treatise of 1044 AD described different formulas for Chinese gun powder, which is a mixture of potassium nitrate (KNO3), carbon, and sulfur. Early alchemists gave sulfur its own alchemical symbol which was a triangle at the top of a cross.
In the late 1770s, Antoine Lavoisier helped convince the scientific community that sulfur was an element and not a compound. In 1867, sulfur was discovered in underground deposits in Louisiana and Texas. The overlying layer of earth was quicksand, prohibiting ordinary mining operations. Therefore the Frasch process was utilized.

Notes

The distinctive colours of Jupiter’s volcanic moon, Io, are from various forms of molten, solid and gaseous sulfur. sulfur has also been found in many types of meteorite.
Hydrogen Sulfide (H2S), is well known for its smell of rotten eggs!

Hazards

Carbon disulfide, carbon oxysulfide, hydrogen sulfide, and sulfur dioxide (SO2) should all be handled with care.
Although sulfur dioxide is sufficiently safe to be used as a food additive in small amounts, at high concentrations it reacts with moisture to form sulfurous acid which in sufficient quantities may harm the lungs, eyes or other tissues. In creatures without lungs such as insects or plants, it otherwise prevents respiration.
Hydrogen sulfide is quite toxic (more toxic than cyanide). Although very pungent at first, it quickly deadens the sense of smell, so potential victims may be unaware of its presence until it is too late.

Sulfur Compounds

Sulfamic acid H3NO3S [Carcinogenic & Toxic]
The most famous applicaton of sulfamic acid is in the synthesis of compounds that taste sweet. It is used as an acidic cleaning agent, typically for metals and ceramics. It is a replacement for hydrochloric acid for the removal of rust.
It’s other uses include; catalyst for esterification process, dye and pigment manufacturing, herbicide, coagulator for urea-formaldehyde resins, ingredient in fire extinguishing media, in the pulp and paper industry as a chloride stabilizer and for the synthesis of nitrous oxide by reaction with nitric acid.

Sulfur dioxide SO2 [Toxic]
It is produced by volcanoes and in various industrial processes. In particular, poor-quality coal and petroleum contain sulfur compounds, and generate sulfur dioxide when burned: the gas reacts with water and atmospheric oxygen to form sulfuric acid (H2SO4) and thus acid rain.
Sulfur dioxide is sometimes used as a preservative in alcoholic drinks, or dried apricots and other dried fruits. The preservative is used to maintain the appearance of the fruit rather than prevent rotting. This can give fruit a distinctive chemical taste. Prior to the development of Freons, sulfur dioxide was used as a refrigerant in home refrigerators.

Sulfuric Acid H2SO4 [Highly Corrosive & Toxic]
Sulfuric acid has many applications, and is produced in greater amounts than any other chemical besides water. World production in 2001 was 165 million tonnes. Principal uses include ore processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis.
Sulfuric acid is produced in the upper atmosphere of Venus by the sun’s photochemical action on carbon dioxide, sulfur dioxide, and water vapour. Ultraviolet photons of wavelengths less than 169 nm can photodissociate carbon dioxide into carbon monoxide and atomic oxygen. Atomic oxygen is highly reactive; when it reacts with sulfur dioxide, a trace component of the Venusian atmosphere, the result is sulfur trioxide, which can combine with water vapour, another trace component of Venus’ atmosphere, to yield sulfuric acid.

Reactions of Sulfur

Reactions with water
Sulfur will not react with water under standard conditions.
Reactions with air
Sulfur burns in air to form sulfur(IV) dioxide.
S8(s) + 8O2(g) --> 8SO2(g)
 
Reactions with halogens
sulfur reacts with fluorine and burns to form sulfur(VI) hexafluoride.
S8(s) + 24F2(g) --> 8SF6(l)
Molten sulfur will react with molten sulfur to form disulfur dichloride.
S8(s) + 4Cl2(g) --> 4S2Cl2(l)
With excess chlorine and in the presence of a catalyst it is possible to make a mixture containing and equilibrium of sulfur(II) chloride and disulfur dichloride.
S2Cl2(l) + Cl2(g) --> 2SCl2(l)
Reactions with acids
Sulphur does not react with dilute non-oxidizing acids.
Reactions with bases
Sulfur reacts with hot aqueous potassium hydroxide to form sulfide and thiosulfate species.
S8(s) + 6KOH(aq) --> 2K2S3 + K2S2O3 + 3H2O(l)

Occurrence of Sulfur

Elemental sulfur can be found near hot springs and volcanic regions in many parts of the world, especially along the Pacific Ring of Fire. Such volcanic deposits are currently mined in Indonesia, Chile, and Japan. Sicily is also famous for its sulfur mines.
Significant deposits of elemental sulfur also exist in salt domes along the coast of the Gulf of Mexico, and in evaporites in eastern Europe and western Asia. The sulfur in these deposits is believed to come from the action of anaerobic bacteria on sulfate minerals, especially gypsum, although apparently native sulfur may be produced by geological processes alone, without the aid of living organisms. However, fossil-based sulfur deposits from salt domes are the basis for commercial production in the United States, Poland, Russia, Turkmenistan, and Ukraine.
Sulfur production through hydrodesulfurization of oil, gas, and the Athabasca Oil Sands has produced a surplus - huge stockpiles of sulfur now exist throughout Alberta, Canada.
Common naturally occurring sulfur compounds include the sulfide minerals, such as pyrite (iron sulfide), cinnabar (mercury sulfide), galena (lead sulfide), sphalerite (zinc sulfide) and stibnite (antimony sulfide); and the sulfates, such as gypsum (calcium sulfate), alunite (potassium aluminium sulfate), and barite (barium sulfate). It occurs naturally in volcanic emissions, such as from hydrothermal vents, and from bacterial action on decaying sulfur-containing organic matter.
The distinctive colours of Jupiter’s volcanic moon, Io, are from various forms of molten, solid and gaseous sulfur. There is also a dark area near the Lunar crater Aristarchus that may be a sulfur deposit. Sulfur is also present in many types of meteorites.

Allotropes of Sulfur

sulfur (S) is second only to carbon in the number of known allotropes formed. The existence of at least twenty-two sulfur allotropes has been demonstrated.
Sulfur forms an extensive series of generally yellow crystalline allotropes, Sn (where species with n up to 30 have been identified). 

Orthorhombic Sulfur [ S8 ]
The most common form, stable at room temperature and atmospheric pressure. Eight sulfur atoms bond covalently in crownlike rings. 

Cyclohexasulfur or Rhombohedral Sulfur [ S6 ]
Cyclohexasulfur was first reported in 1891. It is the densest of the sulfur allotropes and forms air-sensitive orange-red crystals containing chair-shaped, six-membered rings. 

Amorphous Sulfur [ S ]
The result of very rapid cooling of very hot sulfur. 

Disulfur [ S2 ]
The simplest allotrope of sulfur, it is a violet colour. It does not occur naturally at room temperature and pressure. It is commonly generated in the vapour generated from sulfur at temperatures above 700oC.
It has been detected by the Hubble Space Telescope in volcanic eruptions on Jupiter’s satellite, Io.

Isotopes of Sulfur

32S [16 neutrons]
Abundance: 95.02%
Stable with 16 neutrons
33S [17 neutrons]
Abundance: 0.75%
Stable with 17 neutrons 

34S [18 neutrons]
Abundance: 4.21%
Stable with 18 neutrons 

35S [19 neutrons]
Abundance: synthetic
Half life: 87,32 days [ beta- ]
Decay Energy: 0.167 MeV
Decays to 35Cl. 

36S [20 neutrons]
Abundance: 0.02%
Stable with 20 neutrons

BARITE [ Sulfates : Barite ]

BaSO4, barium Sulfate
Barite is a common mineral and makes very attractive specimens. It often is an accessory mineral to other minerals and can make a nice backdrop to brightly coloured crystals. At times bladed or tabular crystals of Barite form a concentric pattern of increasingly larger crystals outward. This has the appearance of a flower and when coloured red by iron stains, these formations are called "Desert Roses". Because Barite is so common, it can be confused for other minerals. Celestite (SrSO4) has the same structure as barite and forms very similar crystals. The two are indistinguishable by ordinary methods, but a flame test can distinguish them.
 
By scrapping the dust of the crystals into a gas flame the colour of the flame will confirm the identity of the crystal. If the flame is a pale green it is barite, but if the flame is red it is celestite. The flame test works because the elements barium (Ba) and strontium (Sr) react in the flame and produce those colours.

Physical Characteristics

Colour: variable but is commonly found colourless or white, also blue, green, yellow and red shades
Luster: vitreous
Transparency: crystals are transparent to translucent
Crystal System: orthorhombic; 2/m 2/m 2/m Crystal Habits: include the bladed crystals that are dominated by two large pinacoid faces top and bottom and small prism faces forming a jutting angle on every side. There are many variations of these faces but the flattened blades and tabular crystals are the most common. If the pinacoid faces become diminished or are absent, the resulting prismatic crystal has a rhombic cross section. Also scaly, lamellar, and even fiberous
Cleavage: perfect in one direction, less so in another direction
Fracture: conchoidal
Hardness: 3 - 3.5
Specific Gravity: approx. 4.5 (heavy for translucent minerals)
Streak: white
Other: green colour in flame test (see above)
Associated Minerals: numerous but significant associations have been with chalcopyrite, calcite, aragonite, sulfur, pyrite, quartz, vanadinite, cerussite and fluorite among many others
Major Occurrences: include Oklahoma, Connecticut and Colorado, USA; England and Germany
Best Indicators: crystal habit, flame test and density

A Paul Alan Freshney Production, login here

Jons Jacob Berzelius [1779-1848]


"The day of a man's funeral seems to be a fitting time for one to ask, 'What kind of man was he? How will history portray him? For what will he be remembered?' I met Berzelius for the first time when I worked with him at the health spa. I was impressed with him then and I hope that your chronicle of him will treat him with the dignity and respect which he deserves. If I did not believe that you would do so, this interview would not now be taking place...""From my early conversations with him, I learned that he had been born in Sorgard. There followed an unhappy childhood. His father, who was a teacher, died while he was still young. His mother remarried and died shortly thereafter. At the age of twelve he was sent away to school in Linkoping, where he supported himself with tutoring. He had an inate ability to learn languages and soon became proficient in both German and French. Perhaps it was this command of languages which led him to try to simplify chemical formulas and symbols. He began his medical studies at the age of seventeen but was forced to withdraw when his scholarship was withdrawn, not, however, before learning a good deal of chemistry from A. G. Eckberg, the discoverer of titanium. In his desire to help Jons, his uncle found him an apprenticeship to a pharmacist. This was followed by an apprenticeship to one of the physicans at the Medivi mineral springs. It was here that he learned the quantitative techniques that would be the foundation for his later work."

"We became friends at this point, and I have kept track of him since." "He resumed his medical studies and received his PhD. His doctoral work centered on galvano therapy: the use of electricity in the treatment of the sick. From here he became an assistant to the professor of surgery at Stockholm. He began a series of chemical investigations in collaboration with a young mine owner by the name of Witssinger. In 1807, he became professor of chemistry at the Karolinska Medical Institute. Here he did much inorganic analysis and brought to the lab the very rigid standards of experimentation which were to be his hallmark until his death." "I hope by this time that you appreciate that the road to his success was not an easy one as in the case of many others who had the wealth to pursue what they would. His persistence was born of an inner fire and drive to achieve, which allowed him to overcome the many obstacles he encountered."

"As I have indicated, he was a driven man and spent most of his life in 'the minute investigations of chemical proportions and, with that, the development of the atomic doctrine he looked upon as his life task'. Sometimes driven men are unhappy men. Not so Jons. The joy which he found in his work can be seen in the quality of his experimentation and most definitely in his teaching. His personal interactions with his students is well documented. To give his students the information which he felt was most correct, he published a textbook which went through several revisions as new materials and theories developed. He even succeeded in introducing chemistry, physics and natural history into the high school curriculum. During this time his meticulous analysis led him to publish several tables of atomic weights. Again these were revised continuously, finally containing over 2000 determinations. The large number came from using the term atomic weight for elements and compounds alike."

"As Boyle might be seen as a man stepping from the tradition of alchemy to that of applied chemistry, so too may Berzelius be seen as a man stepping from the tradition of Lavoisier into that of organic chemistry. He moved from the hierachal duality of acids and salts proposed by Stahl and Lavoisier to his own duality which saw substances composed of the generic and specific and eventually to one of compounds being made up of positive and negative portions. Perhaps it was because 'He saw organic substances as generic mixtures which had to be separated into specific species before anything could be done with them' that his success with organic chemistry was less than with inorganic chemistry."

"He was great in that he had the ability to arrive at the general by way of the particular; and although there may have been errors of interpretation, or what might be considered errors by us, in his assumptions, his final conclusions were free of error due to the meticulous nature of his work."

"Controversies with others will arrive when there is a feeling that error has been made by others and in the records of Berzelilus' work you will find many of them with other chemists such as Dumas, Laurent, and Liebig. As Dumas once observed 'Till now it has been usual to discard a hypothesis as soon as it leads to absurdities, but to some modern investigators this course seems too inconvenient'".

"It is always easier to destroy than to build up. It is easier to criticize the ruins rather than to admire the architecture from which the ruins came. During his later life, he saw the structure of his chemistry begin to crumble in parts. Because of this he tended to become depressed and withdrawn. Yet there remains a good deal in the ruins. Turner's advocacy of the adoption of his atomic symbols before the British Academy of Sciences is one such instance."

"You are free to look at the rest and make of them what you will. For it will be how you subjectively feel about the man that will determine what you will write. However, it might be well to consider what Rose wrote of him:

'The irresistible captivation which Berzelius exercised over those who enjoyed the privilege of a lengthened intercourse with him was only partly due to the lofty genius, whose sparks flashed from all his work, and only partly to the clearness, the marvelous wealth of ideas, and the untiring care and great industry that gave everything with which he had to do the stamp of highest perfection. It was also- and everyone who knew him intimately will agree with this,-it was also those qualities which placed him so high as a man: it was his devotion to others, the noble friendshipwhich he showed to all whom he deemed worthy of it, the great unselfishness and concientiousness, the perfect and just recognition of the services of others,-- in short, it was all those qualities which spring up from an upright and honorable character.'"

GET NEW INFORMATION

SOCIAL NETWORK

CB Blogger