Mei 2011 - Jejaring Kimia

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Mei 29, 2011

Perkembangan Teori Atom dan Struktur Atom

Mei 29, 2011
Sampai saat ini tidak ada satu alatpun yang mampu melihat bentuk dan susunan atom. Oleh karena itu, beberapa ahli membuat suatu model untuk menjelaskan keadaan suatu atom yang sebenarnya. Meskipun belum dapat diketahui dengan pasti, tetapi para ahli dapat menjelaskan kondisi atom melalui gejala-gejala yang dapat ditangkap dari sifat-sifat unsure, sebab atom merupaka bagian terkeci dari unsur.

Penyelidikan tentang atom dimulai dengan ditemukannya sifat listrik dari suatu materi. Apabila sebatang sisir plastic digosokkan pada rambut yang tidak berminyak, maka batang listrik tersebut akan menarik potongan-potongan kecil kertas. Peristiwa itu menunjukkan bahwa sisir mempunyai sifat listrik. Jika ditinjau lebih jauh, maka sisir merupakan materi yang tersusun oleh atom-atom. Dengan demikian dapat disimpulkan bahwa atom mempunyai sifat listrik.

Gejala kelistrikan atom makin menarik para ahli fisika sehingga pada perkembangan selanjutnya diketahui bahwa atom tersusun dari partikel-partikel penyusun atom (partikel sub-atom). Penemuan-penemuan partikel sub-atom menunjukkan bahwa atom merupakan kumpulan partikel sub atom yang tersusun sangat rumit.

Perkembangan ilmu pengetahuan fisika khususnya yang menyangkut fisika atom mengalami kemajuan yang sangat pesat setelah J.J. Thomson menemukan partikel elementer yang dinamakan electron. Penemuan electron ini merupakan hal sangat penting dalam fisika atom sebab dengan penemuan ini telah berhasil mengubah pendapat para ahli fisika pada saat itu. Atom bukan lagi sebagai bagian terkecil dari suatu unsur karena ternyata masih bisa di bagi-bagi lagi ke dalam bagian-bagian lain diantaranya adalah elektron

Bertitik tolak dari penemuan tersebut mulailah para ahli fisika mereka-reka bagaimanakah gambaran atom (model atom) yang sebenarnya. Dimulai oleh Thompson yang dikenal dengan model atom roti kismisnya, kemudian Rutherford, Niels Bohr,dan spectrum hydrogen.

Beberapa hal yang akan dibahas dalam tulisan ini adalah sebagai berikut:
1. Model atom thompson
2. Model atom rutherford dan hamburan partikel alpha
3. Model atom bohr
4. Spektrum atom hidrogen

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Rino Safrizal
Jejaring Kimia Updated at: Mei 29, 2011

Mei 18, 2011

Calcium [Ca]

Mei 18, 2011

Characteristics

An: 20 N: 20
Am: 40.078 g/mol
Group No: 2
Group Name: Alkaline earth metal
Block: s-block Period: 4
State: solid at 298 K
Colour: silvery white Classification: Metallic
Boiling Point: 1757K (1484oC)
Melting Point: 1115K (842oC)
Density: 1.55g/cm3

Discovery Information

Who: Sir Humphrey Davy
When: 1808
Where: England

Name Origin

Latin: calx, calcis (lime). "calcium" in different languages.

Sources

Obtained from minerals like chalk, limestone and marble. Very abundant. Makes up 3.5% of crust (making it the fifth most abundant element). Occurs only in compounds. calcium is found mostly in soil systems as limestone, gypsum (CaSO4 - 2H2O) and fluorite (CaF2). Stalagmites and stalactites contain calcium carbonate (CaCO3).
Annual production is around 112 million tons.

Abundance

Universe: 70 ppm (by weight)
Sun: 70 ppm (by weight)
Carbonaceous meteorite: 11000 ppm
Earth’s Crust: 41000 ppm
Seawater: 390 ppm
Human: 1.4 x 107 ppb by weight, 2.2 x 106 ppb by atoms

Uses

Used for dehydrating oils, decarburization and desulfurization of iron and its alloys, getter in vacuum tubes. Also used as an alloying agent for aluminium, copper and lead, a reducing agent for beryllium and used in fertilizer, concrete and plaster of paris.

 
calcium is an important component of a healthy diet. calcium is an essential component shells, bones, teeth and plant structures.

History

calcium was prepared as lime by the Romans under the name calyx in the 1st century A.D., but the metal was not discovered until 1808. Berzelius and Pontin prepared calcium amalgam by electrolizing lime in mercury. Davy was then successful in isolating the impure metal. Why did it take so long? calcium is the fifth most abundant metallic element in the earth’s crust, but is never found in the elemental form because it is so reactive. It is found in limestone (CaCO3), gypsum (CaSO4.2H2O) and fluorite (CaF2).

Notes

calcium is an important component of a healthy diet. A deficit can affect bone and teeth formation, while over retention can cause kidney stones. Vitamin D is needed to absorb calcium. Dairy products, such as milk and cheese, are a well-known source of calcium.

Hazards

Pure calcium is a shiny soft metal that will react violently with water to release hydrogen and calcium hydroxide. Skin contact may cause burns.

Calcium Compounds

Calcium carbonate CaCO3 : Irritant :
The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or limestone aggregate for roadbuilding or as an ingredient of cement or as the starting material for the preparation of builder’s lime by burning in a kiln.
Calcium carbonate is widely used as an extender in paints, in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble.
Calcium carbonate is also widely used as a filler in plastics. Some typical examples include around 15 to 20% loading of chalk in uPVC drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. Fine ground calcium carbonate is an essential ingredient in the microporous film used in babies nappies and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching.
Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement(1), antacid, and/or phosphate binder. It is also used in the pharmaceutical industry as a base material for tablets of other pharmaceuticals.
As a food additive, it is used in some soy milk products as a source of dietary calcium.

Calcium chloride CaCl2 : Irritant :
Because it is strongly hygroscopic, it can be used to dry air as well as other gases and organic liquids. In this capacity, it is known as a drying agent or desiccant.
Aided by the intense heat evolved during its dissolution, calcium chloride is also used as an ice-melting compound. Unlike the more-common sodium chloride (rock salt or halite), it is relatively harmless to plants and soil. It is also more effective at lower temperatures than sodium chloride.
Calcium chloride tastes extremely salty and is used an ingredient in some foods, especially pickles, to give a salty taste while not increasing the food’s sodium content.

Calcium hypochlorite Ca(ClO)2
Used for the disinfection of drinking water or swimming pool water. For use in outdoor swimming pools, calcium hypochlorite can be used as a sanitiser in combination with a cyanuric acid stabiliser. The stabiliser will reduce the loss of chlorine because of UV radiation.
Calcium hypochlorite (known as ’bleaching powder’) is also used for bleaching cotton and linen and used in the manufacture of chloroform.

Calcium oxide CaO
Used in water and sewage treatment to reduce acidity, to soften, as a flocculant, and to remove phosphates and other impurities; in paper making to dissolve lignin, as a coagulant, and in bleaching; in agriculture to improve acidic soils; and in pollution control - in gas scrubbers to desulfurize waste gases and to treat many liquid effluents. It has traditionally been used in the burial of bodies in open graves, to hide the smell of decomposition.

Hydroxylapatite Ca5(PO4)3(OH)
Hydroxylapatite makes up 70% of bone, carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised.
Lime sulfur
Lime sulfur is sold as a spray for deciduous trees to control fungi, bacteria and insects living or dormant on the surface of the bark. Lime sulfur burns leaves so it is not as useful for evergreen plants.
Bonsai enthusiasts use undiluted lime sulfur to bleach and sterilise portions of trees to give an aged look known as Jin.

Reactions of Calcium

Reactions with water
calcium reacts slowly with water to form calcium hydroxide and hydrogen gas. The calcium metal sinks in water and after an hour or so bubbles of hydrogen are evident, stuck to the surface of the metal.
Ca(s) + 2H2O(g) --> Ca(OH)2(aq) + H2(g)
 
Reactions with air
The surface of calcium metal is covered with a thin layer of oxide that helps protect the metal from attack by air, but to a lesser extent than the corresponding layer in magnesium. Once ignited, calcium burns in air to give a mixture of white calcium oxide and calcium nitride.
2Ca(s) + O2(g) --> 2CaO(s)
3Ca(s) + N2(g) --> Ca3N2(s)
 
Reactions with halogens
calcium is very reactive towards the halogens fluorine, chlorine, bromine and iodine, and burns to form calcium(II) dihalides.
Ca(s) + F2(g) --> CaF2(s)
Ca(s) + Cl2(g) --> CaCl2(s)
Ca(s) + Br2(g) --> CaBr2(s)
Ca(s) + I2(g) --> CaI2(s)
The reactions with bromine and iodine require heat to enable the formation of the products.
Reactions with acids
calcium metal dissolves readily in dilute or concentrated hydrochloric acid to form solutions containing the aquated Ca(II) ion together with hydrogen gas.
Ca(s) + 2HCl(aq) --> Ca2+(aq) + 2Cl-(aq) + H2(g)

Occurrence of Calcium

calcium is not naturally found in its elemental state. calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite (CaMg(CO3)2) and gypsum (CaSO4.2H2O). It occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclase, amphiboles, pyroxenes and garnets.

Isotopes of Calcium

40Ca [20 neutrons]
Abundance: 96.941%
Stable with 20 neutrons 

41Ca [21 neutrons]
Abundance: synthetic
Half life: 1.03 x 105 years [ Electron Capture ]
Decay Energy: ? MeV
Decays to 41K.
41Ca is a radioactive cosmogenic isotope, which has a half-llife of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies. 

42Ca [22 neutrons]
Abundance: 0.647%
Stable with 22 neutrons 

43Ca [23 neutrons]
Abundance: 0.135%
Stable with 23 neutrons 

44Ca [24 neutrons]
Abundance: 2.086%
Stable with 24 neutrons 

45Ca [25 neutrons]
Abundance: synthetic
Half life: 162.7 days [ beta- ]
Decay Energy: 0.258 MeV
Decays to 45Sc. 

46Ca [26 neutrons]
Abundance: 0.004%
Half life: 2.8 x 1015 years [ Double beta decay ]
Decay Energy: ? MeV
Decays to 46Ti. 

47Ca [27 neutrons]
Abundance: synthetic
Half life: 4.536 days [ beta- ]
Decay Energy: 0.694, 1.99 MeV
Decays to 47Sc.
Half life: 4.536 days [ Gamma Radiation ]
Decay Energy: 1.297 MeV
Decays to ?. 

48Ca [28 neutrons]
Abundance: 0.187
Half life: 4 x 1019 years [ Double beta decay ]
Decay Energy: ? MeV
Decays to 48Ti.
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Rino Safrizal
Jejaring Kimia Updated at: Mei 18, 2011

Mei 15, 2011

Molecular Weight Calculator 1.0.1

Mei 15, 2011
Easily calculate molecular weights

This application will enable you to perform molecular weight calculations of any chemical formula.

It is easy to use and accurate, contains embedded periodic table inside for easy insert elemnts fromperiodic table. The application is suitable for students, chemists, scientists, teachers and analysts.

Here are some key features of "Molecular Weight Calculator":

  1. Easy to use molecular weight calculator
  2. Calculate molecular weight or molar mass of any chemical formula
  3. Insert elements from embedded periodic table

Click here to download Molecular Weight Calculator 1.0.1
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Rino Safrizal
Jejaring Kimia Updated at: Mei 15, 2011

Mei 03, 2011

Laju Penyembelihan Ayam, Babi, dan Sapi di Seluruh Dunia

Mei 03, 2011

  1. Ayam: 16.887.556.000 per tahun (16,9 miliar per tahun) atau 535 per detik
  2. Babi: 989.764.000 per tahun (989,8 juta per tahun) atau 31,38 per detik
  3. Sapi: 1.383.157.000 per tahun (1,4 miliar per tahun) atau 43,85 per detik

Unduh atau saksikan video selengkapnya  di sini
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Rino Safrizal
Jejaring Kimia Updated at: Mei 03, 2011

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