An alum is a type of chemical compound, usually a hydrated double sulfate salt of aluminum with the general formula X Al (SO > 4 )
2 Ã, Â · 12H
2 O , where X is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the formula KAl (SO
4 )
2 Ã , Â · 12H
2 O . Other cans are named after monovalent ions, such as alum sodium and alum ammonium.
The name "alum" is also used, more generally, for salts of the same formula and structure, except that aluminum is replaced by other trivalent metal ions such as chromium (III), and/or sulfur replaced by other chalcogens such as selenium. The most common of these analogs is the alum krom KCr (SO
4 )
2 Ã, Â · 12H < span>
2 O .
In some industries, the name "alum" (or "alum papermaker") is used to refer to aluminum sulfate Al
2 (SO
4 )
3 Ã, Â · n H
2 O . Most industrial flocculations made with "alum" actually use aluminum sulfate. In medicine, "alum" can also refer to aluminum hydroxide gel used as an adjuvant vaccine.
Video Alum
Primary type
Alum aluminum is named by monovalent cations. Unlike other alkali metals, lithium does not form alum; a fact that is associated with the small size of the ion.
Alum yang paling penting adalah
- Tawas kalium, KAl (SO
4 )
2 Â · 12H
2 O , juga disebut "potash alum" atau hanya "tawas". - Sodium tawas, NaAl (SO
4 )
2 Â · 12H
2 O , juga disebut "soda alum" atau "SAS". - Tawas amonium, NH
4 Al (SO
4 )
2 Â · 12H
2 O .
Maps Alum
Sifat kimia
Alum aluminum has a number of common chemical properties. They dissolve in water, have a sweet taste, react acid to litmus, and crystallize in ordinary octahedra. In alum, each metal ion is surrounded by six water molecules. When heated, they melt, and if the heating continues, the crystallization water is moved, the salt scum and swell, and finally the amorphous powder remains. They are astringent and acidic.
Crystal Structure
The aluminum crystallizes in one of three different crystalline structures. These classes are called? -? - and? -alum.
Solubility
Solubility of various alum in water varies greatly, alum sodium is soluble in water, while alum cesium and rubidium are only slightly soluble. Various solubilities are shown in the following table.
- At T , 100 parts of soluble water:
Usage
Alum based aluminum has been used since antiquity, and is still important in many industrial processes.
The most commonly used alum is the potassium alum. It was used since antiquity as a flocculant to clarify turbid liquid, as mordan in dying, and in tanning. It is still widely used to purify tap water, in pharmaceuticals, for cosmetics (in deodorant and antitranspirant), in food preparation (in baking powder and pickle), and paper and fire resistant fabrics.
Sodium alum is used in substitution to potassium alum in baking powder. Tawas ammonium has several uses for the niche. Other alumni have the most research interest.
In traditional Japanese art, alum and animal glue dissolved in water, forming a liquid known as dousa (ja: ??), and used as a bottom layer for paper size.
Alum in the form of potassium aluminum sulfate in a concentrated hot water bath regularly used by jewelers and mechanical sellers to dissolve hardened hard steel drill bits on articles made of aluminum, copper, brass, gold (any rust) and silver (both sterling and fine). This is because alum does not react chemically to a significant degree with these metals, but will corrode steel. When the heat is applied to the alum mixture that holds a piece of work that has a drill bit trapped inside it, if the missing bit is small enough, it can sometimes be dissolved within a few hours.
History
In antiquity and the Middle Ages
A detailed description of a substance called alumen occurs in Pliny the Elder's Natural History . By comparing this with the stupteria account given by Dioscorides, both are identical. Pliny tells us that an alode form is found naturally on earth, and calls it salsugoterrae .
Pliny writes that different substances are distinguished by the aliens name, but they are all characterized by a certain level of astringency, and they are all used in dyeing and medicine. Pliny says that there is another type of alum called the Greek schist , and which is "divided into filaments with whitish color", From the name schiston and the formation mode, It appears that this species is a salt which are formed spontaneously in certain salty minerals, such as slate and bitumen flakes, and mainly consist of iron and aluminum sulfate. One of the alien species is a liquid, which tends to be falsified; but when it is pure it has a blackened nature when added to the pomegranate juice. This property appears to be characteristic of iron sulfate solutions in water; ordinary alum solution (potassium) will not have such properties. Contamination with iron sulphate is highly disliked due to the color of this dark and dull dye. In some places the iron sulfate may be less, so the salt will be white and will fit, according to Pliny, to dye the bright colors.
Pliny describes several other species of alumen but it is unclear as to what these minerals are. The alumen of the ancestor, not always alum potassium, not even alkali aluminum sulfate.
The production of potassium alum from alunite is archaeologically proven on the island of Lesbos. The site was abandoned in the 7th century but dates back at least to the 2nd century.
Native alumen dari Melos tampaknya telah menjadi campuran terutama dari alun-alun ( Al
2 (SO
4 )
3 Â · 17H
2 O ) dengan tawas kalium dan sulfat minor lainnya.
Gurun barat Mesir adalah sumber utama pengganti alum di jaman dahulu. Evaporit ini terutama FeAl
2 (SO < span>
4 )
4 Â · 22H
2 O , MgAl
2 (SO
4 )
4 Â · 22H
2 O , NaAl (SO
4 )
2
2 O , MgSO
4 Â · 7H
2 O dan Al
2 (SO
4 )
3 Â · 17H
2 O .
Tawas and green vitriol (iron sulfate) both have a sweet and astringent taste, and they have overlapping usage. Therefore, through the Middle Ages, alchemists and other authors did not seem to distinguish two salts accurately from each other. In the alchemist's writings we find the words misy , sory , and chalcanthum applied to one of the compounds; and the name atramentum sutorium , which may be thought to belong to green vitriol, is applied indifferently to both.
Modern understanding of alum
In the early 1700s Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a kind of alum: The error was immediately corrected by Johann Pott and Andreas Marggraf, which showed that the deposits obtained when the alkali was poured into the alum solution, ie alumina, were very different of lime and lime, and is one of the materials in ordinary clay.
Marggraf also showed that the perfect crystals with alum properties can be obtained by dissolving alumina in sulfuric acid and adding potas or ammonia to the concentrated solution. In 1767, Torbern Bergman observed the need for potassium or ammonium sulfate to convert aluminum sulfate into alum, while sodium or calcium would not work.
The general alum composition was ultimately determined by Louis Vauquelin in 1797. As soon as Martin Klaproth discovered the presence of potassium in leukite and lepidolite, Vauquelin showed that the common alum is a double salt, composed of sulfuric acid, alumina, and potassium. In the same volume of volumes, Jean-Antoine Chaptal published an analysis of four different types of alum, namely, the Romans, Lev's alum, alum and the self-produced English alum, confirming the results of Vauquelin.
Production
Some alum appears as a mineral, the most important being alunite.
The most important aluminum - potassium, sodium, and ammonium - is produced industrially. A typical recipe involves combining aluminum sulfate and monovalent sulphate cations. Aluminum sulfate is usually obtained by treating minerals such as alum sekis, bauxite and cryolite with sulfuric acid.
Related compound
Many trivalent metals are capable of forming alum. The general form of alum is XM (SO 4 ) 2 /sub> O, where X is an alkali or ammonium metal, M is a trivalent metal, and n often is 12. The most important example KCr (SO
4 span>
2 sub style = "font-size: inherited; line-height: inherited; vertical-align: baseline"> 2 O , dark violet crystalline double sulfate from chromium and potassium in tanning.
In general, alum is formed more easily when the alkali metal atom is larger. This rule was first stated by Locke in 1902, which found that if trivalent metal does not form alum cesium, it will not form alum with other alkali metals or with ammonium.
almen containing Selenate
Selenium or selenate alum is also known to contain selenium in the sulfur site in sulfate anions, making selenat ( SeO 2 -
4 ) instead. They are powerful oxidizing agents.
Compact mix
In some cases, aluminum solid solutions with different monovalent and trivalent cations may occur.
Other Hydrates
In addition to alum, which is a dodecahydrate, double sulfate and a cation of univalent and trivalent cations occur with other degrees of hydration. These materials can also be referred to as alum, including undecahydrates such as mendozite and calinite, hexahydrates such as guanidinium ( CH
6 N
3 ) and dimethylammonium ( (CH 3 )
2 NH
2 ) "alaw", tetrahidr at such as goldichit, monohydrate such as thallium plutonium sulfate and anhydrous alum (yavapaiites). These classes include different, but overlapping, ionic combinations. Other double sulfates
Sebuah alum pseudo adalah sulfat ganda dari rumus khas A SO
4 Â · B
2 (SO
4 )
3 Â · 22H
2 O , di mana A adalah ion logam divalen, seperti kobalt (wupatkiite), mangan (apjohnite), magnesium (pickingerite) atau besi (halotrichite atau tawas bulu), dan B adalah ion logam trivalen.
Sulfat ganda dengan rumus umum A
2 SO
4 Â · B
2 (SO
4 )
3 Â · 24H
2 O juga diketahui, di mana A adalah kation monovalen seperti natrium, kalium, rubidium, cesium, atau thallium (I), atau senyawa kation seperti ammonium ( NH
4 ), methylammonium ( CH
3 NH
3 ), hydroxylammonium ( HONH < sup style = "font-size: mewarisi; line-height: mewarisi; vertical-align: baseline">
3 ) atau hydrazinium ( N
2 H
5 ), B adalah ion logam trivalen, seperti aluminium, kromium, titanium, mangan, vanadium, besi (III), kobalt (II) I), galium, molibdenum, indium, rutenium, rodium, atau iridium. Selenat analog juga terjadi. Kemungkinan kombinasi kation univalen, kation trivalen, dan anion tergantung pada ukuran ion.
Garam Tutton adalah sulfat ganda dari rumus khas A
2 SO
4 Â · B SO
4 Â · 6H
2 O , di mana A adalah kation univalen, dan B ion logam divalen.
Double sulfate of composition A
2 SO
4 Ã, Â · 2 < i> B SO
4 , where A is a univalent cation and B is a divalent metal ion called the langbeinites, after potassium potassium magnesium sulfate.
See also
- Mineral list
- Photo prints of gum bichromates and other similar processes using alum, sometimes as colloidal hardeners (gelatin, albumen)
References
- This article incorporates text from publications now in the public domain: Ã, Chisholm, Hugh, ed. (1911). "Alum". EncyclopÃÆ'Â|dia Britannica . 1 (issue 11). Cambridge University Press. pp.Ã, 766-767.
External links
- Media related to Alum in Wikimedia Commons
Source of the article : Wikipedia
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