Science Dictionary » Chemistry

Definition of Magnetic Movement

aman — Fri, 29 Jan 2010 19:58:14 +0000

Magnetic Movement refers to the Ratio between the Maximum Torque (T_max) exerted on a Magnet, Current carrying Coil, or moving charge situated in a Magnetic Field and the strength of that field. It may be thus a measure of the strength of a Magnet or Current carrying Coil.

Definition of Optical Rotation

aman — Fri, 29 Jan 2010 19:33:55 +0000

Optical Rotation is the angle of rotation of plane polarized light by an optically active compound, Optical Rotation having another name which is Optical Activity.

Definition of Optical Activity

djeet — Fri, 29 Jan 2010 19:29:16 +0000

Optical Activity is a Property possessed by certain substances (mainly organic) and their solutions, of rotating the plane of polarized light. the degree of Rotation in a solution is proportional to the concentration of the solute, the distance the light travels through the solution, and the wavelength of the light. Optical Activity, sometimes known as Optical Rotation.

Definition of Optical Isomerism

aman — Fri, 29 Jan 2010 12:20:46 +0000

Optical Isomerism refers to the Isomerism of a Compound which does not possess a structure which can be Superimposed upon that of its Mirror Image.

Definition of Zeolites

aman — Thu, 24 Sep 2009 12:52:06 +0000

Zeolites are shape selective catalyst which have honey-comb like structure. Zeolites have a pore size between 260 pm to 740 pm which makes them possess, the unique property of shape-selectivity of Zeolites. Chemically, Zeolites are micro porous alumino silicates with three dimensional networks of silicates in which some silicon atoms are replaced by aluminium atom giving Al-O-Si framework.

The general chemical formula of Zeolites is M_x/n [(AlO₂)_x (SiO₃)_y].mH₂O and may be considered as open structure of silica in which aluminium has been substituted in a fraction x/(x+y) of its tetrahedral sites.

Example of Homogeneous Catalyst

djeet — Tue, 22 Sep 2009 19:07:12 +0000

Example of Homogeneous Catalyst : Oxidation of sulphur dioxide to form sulphur trioxide in presence of nitric oxide. Here, nitric oxide acts as a catalyst and reactants and catalyst are in same phase i.e. gaseous phase.

Example of Zeolites

djeet — Tue, 22 Sep 2009 18:47:12 +0000

Example of Zeolites : ZSM-5 is a commercially important Zeolite which is used to convert alcohol to gasoline (petrol).

Example of Catalyst

djeet — Tue, 22 Sep 2009 17:49:44 +0000

Example of Catalyst : Decomposition of Potassium chlorate is a slow process which occurs in temperature range of 653-873 K. But when manganese dioxide is added, the rate of reaction increases and decomposition occurs at 473-633 K. In this reaction, manganese dioxide acts as a Catalyst.

Definition of Shape Selectivity of Zeolites

djeet — Tue, 22 Sep 2009 16:57:09 +0000

The ability of Zeolites molecules to selectively catalyze the reactant(s) is called shape-selectivity of Zeolites. The ability of selectively catalyzing the reactants is achieved through their pore structure. The size of the pores in Zeolites varies from 260 to 740 pm. Thus, the molecules which are small enough to enter these pores are absorbed by Zeolites. Catalysis of only adsorbed molecules takes place. Depending on the size of reactant and product molecules compared to size of pores, reaction proceeds in a specific manner. Therefore, Zeolites perform selective-catalysis due to their unique pore structure or shape.

Definition of Shape Selective Catalyst

djeet — Tue, 22 Sep 2009 12:24:09 +0000

The catalyst which alters the rate of chemical reaction due to their unique pore structure is called Shape Selective Catalyst.