Colloidal state substance

As it is now possible by choice of suitable conditions to prepare most compounds in this form, the colloid state should be considered as a physical state in which all substances can be made to exist. Many ma terials such as proteins, vegetable fibres, rubber, etc. are most stable or occur naturally in the colloidal slate. In the colloidal stale the properties of surface are all-important. 

The weathering process which eventually reduces the rock of the parent material to the inorganic constituents of soil comprises both physical and chemical changes. Size reduction from rocks to the colloidal state depends not only upon the mechanical action of natural forces but also on chemical solubilisation of certain minerals, action of plant roots, and the effects of organic substances formed by biological activity. 

An important consequence of the smallness of the size of colloidal particles is that the ratio of surface area to weight is extremely large. Phenomena, such as adsorption, which depend upon the size of the surface will therefore play an important part with substances in the colloidal state. 

Many chemical changes occurring in living processes are catalyzed by enzymes which are complex protein substances produced by living cells. Enzymes are often present in colloidal state and are very specific in their catalytic action. Zymase obtained from yeast catalyses the fermentation of dextrose but is ineffective in breakdown of cane sugar. 

Graham s definitions were expanded, and the concept of a colloidal state of matter evolved. According to this view, a substance could occur in a colloidal state just as it could occur under various conditions as a gas, liquid, or solid. If a colloidal solution was, at that time, defined as a solution in which the dispersed particles were comprised of large molecules, the ascertion would have been more acceptable. 

When the diameter of the particles of a substance dispersed in a solvent ranges Ifom about 10 A to 2000 A, the system is called colloidal solution, colloidal dispersion or simply a colloid. The material with particle size in the colloidal range is said to be in the colloidal state. 

Colloidal solutions (also known as sols) can be prepared by different methods depending on the nature of the substances. Many substances., e.g., gelatin, starch etc. form colloidal solutions by merely dissolving them in water. Metals and inorganic substances are brought into the colloidal state by special methods. Two types of methods are mainly used ... 

A substance which passes into the colloidal state, simply by bringing it in contact with water is known as hydrophilic colloid (hydro = water, philic = loving). But if any solvent like organic liquid is used instead of water, then the more general term lyophilic colloid (lyo = solvent philic = loving) is used. Gum, starch, soap are lyophilic colloids. These colloids when once precipitated can again be brought back directly into the colloidal state. Hence, they are also known as reversible colloids. (Colloidal state precipitate). Reversible colloids are also termed as resoluble or non-electrocratic colloids. 

Substances like metals, metal sulphides cannot be brought into the colloidal state simply by bringing them in contact with water and, therefore, special methods are devised for the purpose. Hence, they are known as hydrophobic colloids (hydro = water phobic = hating). In case of solvent other than water, the general term lyophobic is used. Further, if these colloids are precipitated, then it is not very easy to reconvert the precipitate directly into the colloidal state. Hence, they are termed as irreversible colloids (colloidal state — precipitate), irresoluble or electrocratic colloids. 

Preventing coagulation of a colloidal solution by any means is known as stabilising the colloid. Bancroft (1915) gave the position with regard to Stability. He said that any substance may be brought into a colloidal state, provided the particles of the dispersed phase are so small that the Brownian movement keeps the particles suspended and provided the coagulation of the particles is prevented by a suitable surface film... 

Humic substances (HS) are polymeric oxidation products that result from the decomposition of plant and animal residues. As a consequence of their colloidal state in natural waters, they play an important role in the transport of organic pollutants. Thus hydrophobic organic pollutants such as polycyclic aromatic hydrocarbons, DDT, and PCBs are known to bind well to humic substances, thereby enhancing the former s water solubility. One important characteristic of... 

The colloidal state of matter is distinguished by a certain range of particle size, as a consequence of which certain characteristic properties become apparent. Colloidal properties are in general exhibited by substances of particle size ranging between 0 2 /an and 5 nm (2 x 10"7 and 5 x 10"9 m). Ordinary filter paper will retain particles up to a diameter of 10-20/an (1-2 x 10" 5 m), so that colloidal solutions, just like true solutions, pass through an ordinary filter paper (the size of ions is of the order of 0-1 nm = 10 10 m). The limit of vision under the microscope is about 5-10 nm (5-10 x 10 9 m). Colloidal solutions are therefore not true solutions. Close examination shows that they are not homogeneous, but consist of suspension of solid or liquid particles in a liquid. Such a mixture is known as a disperse system the liquid (usually water in qualitative analysis) is called the dispersion medium and the colloid the disperse phase. 

The colloidal state of matter is characterised by an intimate admixture of at least two phases—the dispersed phase and the dispersion medium, by a dispersion of this kind is meant the regular distribution of one substance into another in such a way that the individual particles of the one substance are suspended separately from each other in the second substance— in this case, the air. In this sense smoke is to be regarded as a two-phase colloid whose dispersion medium (air) is in the gaseous state and w hose dispersed phase is a solid or a liquid. So-called colloidal solutions of this kind have physical and chemical behavior entirely ttifferent from norinal solutions (such as sugar in water), in that the size of the particles may vary within certain limit. without causing the solution to lose its colloidal character. 

See mass. (1) States There are three generally accepted states (phases) in which substances can exist, i.e., solid, liquid, and gas (vapor). From time to time it has been proposed that specialized forms of matter be regarded as states, such as the vitreous (glassy) state, the colloidal state, and the plasma state, but none of these suggestions has gained substantial acceptance. 

The student of chemistry should not overlook that which is known as the colloidal state of matter. In the forerunning part of this book we learned something about solutions. Substances like sugar, salt, etc., are called crystalloids because they dre able to pass into solution and may be again restored to their original condition by evaporating the liquid in which they are dissolved. 

Further complications are due to the interference of a colloidal state that does not involve covalent bonds. This interference definitely plays a role in the structure and, consequently, the properties of phenolic compounds in wine. The colloidal state is, however, difficult to smdy, as it is modified by any manipulation of these substances (Section 9.3). 

The work of Graham was of fundamental importance but his classification of all substances into crystalloids and colloids is not always right many colloids, like some proteins, can be crystallized. On the other hand, almost all so-called crystalloids can be prepared in the colloidal state. 

The microparticles that make up the coating can be of any desired substance composition wise which can be reduced to a colloidal state of subdivision however, they must be dispersible in a medium as a colloidal dispersion. Water is the best medium for dispersions of particles of varying ionic charges. Examples of suitable aqueous sols are amorphous silica, iron oxide, alumina, thoria, titania, zirconia, zircon, and alumina sihcates, including colloidal clays such as montmorillonite, colloidal kaolin, attapul-gite, and hectorite. Silica is preferred material because of its low order of chemical activity, its ready dispersibility, and the easy availabihty of aqueous sols of various concentrations. 

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