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Intuition Pemikiran sehari-hari yang ga penting
Sabtu, 03 April 2010
Hungry Fish
Pembuatan Etil Asetat Melalui Reaksi Esterifikasi Sintesis ester ini merupakan salah satu materi praktikum di Lab Kimia Dasar FMIPA UGM. Mudahmudahan dengan adanya tulisan ini dapat membantu praktikan untuk mengerjakan tugasnya. ^0^ Ok, let's begin Suatu ester asam karboksilat ialah suatu senyawa yang mengandung gugus -CO2R dengan R dapat berbentuk alkil ataupun aril. Suatu ester dapat dibentuk dengan suatu asam karboksilat dengan suatu alkohol, reaksi ini disebut reaksi esterifikasi. Esterifikasi berkataliskan asam dan merupakan reaksi yang reversibel. Karena bersifat reversibel, untuk memperoleh rendemen yang tinggi dari ester itu, kesetimbangan harus digeser ke kanan yaitu ke arah produk (sisi ester). Percobaan ini menggunakan prinsip esterifikasi Fischer yaitu reaksi pembentukan ester dengan cara merefluks sebuah asam karboksilat bersama sebuah alkohol dengan katalis asam. Untuk pembuatan etil asetat, reaksi esterifikasi yang terjadi dalam praktikum ini:
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Blog Archive t 2010 (9)
Penjelasan lebih lanjut mengenai esterifikasi bisa dilihat disini.
November (1)
Seperti banyak reaksi aldehida dan keton, esterifikasi suatu asam karboksilat melalui serangkaian tahap protonasi dan deprotonasi. Oksigen karbonil diprotonasi, alkohol nukleofilik menyerang karbon positif, dan eliminasi air akan menghasilkan ester yang dimaksud. Adapun mekanisme reaksi dari pembuatan etil asetat adalah:
Oktober (1) September (1) Juli (1) Mei (1) t April (3) Pembuatan Etil Asetat Melalui Reaksi Esterifikasi PRECERAMIC INORGANIC POLYMERS Orphan Maret (1)
Untuk setiap tahapan mekanisme esterifikasi yang lebih detail bisa klik disini. Adapun Format Laporan Percobaan A-3 ini
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Labels Chemistry (1) material science (1) movie (1) TV drama (1)
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yah, klo kayanya ga jelas tulisannya, bisa lihat versi pdf di Scribd.
Follow me on Twitter ^0^ Diposting oleh Rei di 21.56
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Label: Chemistry
Yang mampir,,
PRECERAMIC INORGANIC POLYMERS
Mampir yuuk,,
Linear, branched, or cyclolinear polymers or oligomers can be fabricated easily by solution or meltfabrication techniques. If a polymeric material that has been shaped and fabricated in this way is then cross-linked and pyrolyzed in an inert atmosphere to drive off the organic components (typically the side groups), the resultant residue may be a totally inorganic ceramic in the shape of fabricated article. Thus, ceramic fibers, film, coatings, and shaped objects may accessible without recourse to the ultra high temperatures needed for melting of the ceramic materials itself. Note, however, that although the final shape of the object may be retained during pyrolysis, the size will be diminished due to the loss of volatile material. If the pyrolisis takes places too quickly, this contraction process may cause cracking of the material and loss of strength. Moreover, too rapid a rate of heating before or during the initial cross-linking step may cause the polymer intermediate to melt and lose its shape, or the polymer may depolymerize and the product volatilize. Thus, the temperature program or the sequence and rate at which the temperature is raised can have a profound influence on the final properties. THE SOL-GEL PROCESS TO OXIDE CERAMICS (Note: the use of techniques for the low temperature preparation of oxide ceramics such as silica, this process can also be used to produce alumina, titanium oxide, or other metal oxides) Starting in the 1950s a process was developed that leads from small-molecule silicon alkoxides such as tetraethoxysiloxane (tetraethyl orthosilicate), to organosiloxan oligomers and low polymers, and eventually to silica via a “low temperature” synthesis route. A simplified outline of the basic chemistry is shown in reaction (1)-(3), where R is an ethyl or higher alkyl unit. Any or all of the Si-OR bonds can be hydrolyzed to Si-OH functional groups, and these are able to condense to form Si-O-Si linkages. The linear polymers formed in reaction (1) can undergo further alkoxide hydrolysis to give the cross-linked species, also formed in reaction (2), and these cross-linked polymers may further cross-link to give an ultra structure similar the one formed in reaction (3).
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Figure 9.4. Reaction conditions exert a strong influence on the course of sol-gel polymerization reaction. Basic pH, higher temperatures, and grater dilutions favor the formation of rings and rings clusters, as shown in the pathway on the left. Acidic pH, lower temperatures, and higher concentrations favor the formation of chains and dendritic structures. Processing conditions also determine the types of products that are formed, as shown in figure 9,5. For example, fibers can be pulled from a system that contains colloidal clusters that have not yet gelled. Evaporation of a colloidal suspension or a solution may give a “xerogel” coating. Once the system has gelled, extraction of the remaining small molecules using a volatile solvent will leave an “aerogel” which has volume and shape, but is mostly unfilled space. Such materials have been used in flotation devices, lightweight structural materials, or filters. Evaporation of the solvent from a gel allows contraction of the system to a xerogel, and subsequent heating above the melting point gives a dense glass. This a way to produce lens performs. Composite materials called “creamer” are accessible if water-or alcohol-soluble organic polymer is included in the original reaction mixture. The organic polymer raises the impact resistance of the final ceramic.
This article is taken from : Mark, James E., Allcock, Hary R., and West, Robert, 2005, Inorganic Polymers, second edition, Oxford University Press Inc., New York Note : this page is incomplete, there are some pictures not uploaded, please wait for further improvement Diposting oleh Rei di 21.32
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Label: material science
Jumat, 02 April 2010
Orphan Just watched Orphan last night. Actually I'm expecting something like The Omen, but unfortunately i missed
It's some kind of thriller/ murder/ insane person Yah, like other Hollywood horror movies, with some bloody scenes, some murder scenes, and (I tell you) there were no spiritual phenomenon. But it successfully make my heart beat faster >_< and really want to beat Esther (the main villain--girl in movie poster) to death (lol)--and actually she die in last scene in freezing lake. Fiuuh,, It's all began when Kate and John Coleman adopted Esther, a nine years old orphan to heal their lost from an unborn baby. She looked like a cheerful and mature girl, but inside she's evil. Whenever she go, she created trouble. Once she killed a woman from orphanage because she want to tracked down her origin, then she tried to kill Danny (son of Susan and john Coleman) because his attempt to reveal proof for her act. All of her actions aimed to protect her secret, and all revealed in last minutes (it's quiet surprising in fact).. I want to give thumbs up for Isabelle Fuhrman who acted as Esther, she's a talented and beautiful girl (only 13 years old!!).
And it's some of Orphan's scenes
Diposting oleh Rei di 21.06
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Label: movie
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Moreover, step (1) could generate six-, eight-, or higher membered rings instead of chains and these rings may couple to yield clusters of ring (reactions sequence (4)). Although cyclic trimeric siloxane rings are shown for simplicity in reaction (4), the most probable products are cyclic tetramers and higher cyclics. Reaction (2) could also generate cage structures and these too could become linked to formed clusters. Subsequently, the alkoxy groups in the other boundaries of the ring or cage clusters can hydrolyze and couple to yield clusters of clusters, and so on. Ring clusters may, in principle, react with chain clusters or linier polymers to increase the structure complexity. Eventually a catastrophic gelation of the system will occur, and what was originally a solution or a colloid sol become solvent-swollen solid in the shape of the original reaction vessel or mold. Subsequent heating to drive off water and alcohol will complete the condensation process and leave an amorphous form of silica. The complexity of this reaction mechanism is legendary. The reaction pathways and types of product change with variations in pH, the nature of the alkoxy group OR, the rate which water and alcohol are removed during heating, the type of solvent, the present of other metal alkoxides, or the existence of functional organic molecules that can enter into the condensation process. The addition of transition metal akoxides provides a means for the introduction of color into the final ceramic, an option that is useful for the fabrication of optical fillers, colored coating, or ceramic art object. Variations in pH, concentration, and temperature have a profound effect in the condensation pathway. Acidic media, high concentrations of reagents and lower temperatures favor the formation of chains or loosely cross-linked chains. Basic media, dilute solutions, or higher temperatures favor the formation of rings, cages, and cluster networks. (Figure 9.4)
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