Rabu, 29 Februari 2012

Artikel Kimia

Artikel Kimia


Manfaat koloid dalam Penjernihan Air

Posted: 29 Feb 2012 04:49 AM PST

Manfaat koloid dalam Penjernihan Air

Air keran (PDAM) yang ada saat ini mengandung partikel-partikel koloid tanah liat,lumpur, dan berbagai partikel lainnya yang bermuatan negatif. Oleh karena itu, untuk menjadikannya layak untuk diminum, harus dilakukan beberapa langkah agar partikel koloid tersebut dapat dipisahkan. Hal itu dilakukan dengan cara menambahkan tawas (Al2SO4)3.Ion Al3+ yang terdapat pada tawas tersebut akan terhidroslisis membentuk partikel koloid Al(OH)3 yang bermuatan positif melalui reaksi:

Al3+ + 3H2O ->Al(OH)3 + 3H+

Setelah itu, Al(OH)3 menghilangkan muatan-muatan negatif dari partikel koloid tanah liat/lumpur dan terjadi koagulasi pada lumpur. Lumpur tersebut kemudian mengendap bersama tawas yang juga mengendap karena pengaruh gravitasi.

Manfaat koloid dalam Penjernihan Air

What the differences among conductors, semiconductor, and super-conductors

Posted: 29 Feb 2012 02:05 AM PST

Conductors

In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons (see electrical conduction). Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such as in the electrolyte of a battery.

Insulators are non-conducting materials with fewer mobile charges, which resist the flow of electric current. All conductors contain electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the direct current is proportional to the voltage (as determined by Ohm’s law), provided the temperature remains constant and the material remains in the same shape and state. Most familiar conductors are metallic. Copper is the most common material used for electrical wiring. Silver is the best conductor, but is expensive. Because it does not corrode, gold is used for high-quality surface-to-surface contacts. However, there are also many non-metallic conductors, including graphite, solutions of salts, and all plasmas. There are even conductive polymers. See electrical conduction for more information on the physical mechanism for charge flow in materials.

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow (as opposed to ionic conductivity) intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter. Semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Similarly, semiconductor solar photovoltaic panels directly convert light energy into electrical energy. In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current is often schematized as being carried either by the flow of electrons or by the flow of positively charged “holes” in the electron structure of the material. Actually, however, in both cases only electron movements are involved. Common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions. Such compounds share with better known semiconductors intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon and are generally used in thin film structures, which are less demanding for as concerns the electronic quality of the material and thus are relatively insensitive to impurities and radiation damage. Organic semiconductors, that is, organic materials with properties resembling conventional semiconductors, are also known.

Superconductor

  A superconductor is an element, inter-metallic alloy, or compound that will conduct electricity without resistance below a certain temperature. Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is also characterized by a phenomenon called the Meissner effect, the ejection of any sufficiently weak magnetic field from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of “perfect conductivity” in classical physics. The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of copper shows some resistance. Despite these imperfections, in a superconductor the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. Resistance is undesirable because it produces losses in the energy flowing through the material. Once set in motion, electrical current will flow forever in a closed loop of superconducting material making it the closest thing to perpetual motion in nature.

Selasa, 28 Februari 2012

Artikel Kimia

Artikel Kimia


Jenis Koloid Buih

Posted: 28 Feb 2012 07:36 AM PST

Jenis Koloid Buih

Jenis Koloid Buih adalah sistem koloid dari gas yang terdispersi dalam zat cair.

Contoh: sabun, detergen, protein.

sabun/detergen adalah zat yang molekulnya terdiri atas hidrofob dan sekaligus gugus hidrofil.

Zat-zat yang dapat memecah/mencegah buih yaitu eter, isoamil alkohol.

Jenis Koloid Buih

Prosedur Praktikum Sintesis Senyawa Hidrat

Posted: 28 Feb 2012 02:05 AM PST

Bahan Sintesis Senyawa Hidrat

Bahan-bahan yang digunakan dalam percobaan ini adalah: (NH4)2 SO4, ZnSO4. 7H2O, alkohol, tissue roll, kertas saring dan Aquadest.

Alat Sintesis Senyawa Hidrat

Alat-alat yang digunakan dalam percobaan ini adalah: gelas kimia 50 ml; 250 ml ; 500 ml, labu erlenmeyer 250 ml, batang pengaduk, gegep, bunsen, kawat kasa, kaki tiga, sendok tanduk, corong, dan neraca analitik.

Prosedur Sintesis Senyawa Hidrat

Sebanyak 2,08 gram (NH4)2SO4 ditimbang dengan neraca ohaus. Sebanyak 4,52 gram ZnSO4.7H2O ditimbang dengan menggunakan gelas kimia yang berbeda. Kemudian (NH4)2SO4 dan ZnSO4.7H2O yang telah ditimbang tadi dicampurkan ke dalam gelas kimia. Hasil campuran tadi dilarutkan dengan menggunakan air panas, kemudian dipanaskan kembali hingga terbentuk endapan. Endapan yang diperoleh dilarutkan dalam alkohol untuk mempercepat kristalisasi kemudian diaduk. Campuran tadi didinginkan selama beberapa menit kemudian disaring dengan kertas saring. Endapan yang diperoleh kemudian dikeringkan dengan cara dimasukkan ke dalam desikator, setelah kering endapannya ditimbang untuk memperoleh nilai rendamennya.