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Home >> Chemistry Dictionary >>Electrophoresis - Emulsifying Agent
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Electrophoresis. The migration of charged particles, colloidal particles or ions though a solution under an electric field. Variation solution of pH can stop movement at the isoelectric point. In electro-osmosis there is a constant flow of liquid relative to a stationary surface. Electrophoresis is used in analysis, particularly in biochemical applications (iconography, zone electrophoresis, electro-chromatography) for both identification and separation.
Electroplating. A method of plating one metal with another by electrode position. The articles to be plated are made the cathode of an electrolytic cell and a rod or bar of the plating metal is made the anode. Electroplating is used for covering metal with a decorative, more expensive or corrosion-resistant layer of another metal.
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Electroplating. A method of plating one metal with another by electrode position. The articles to be plated are made the cathode of an electrolytic cell and a rod or bar of the plating metal is made the anode. Electroplating is used for covering metal with a decorative, more expensive or corrosion-resistant layer of another metal.
Electrophilic addition. A reaction which involves the addition of a small molecule to an unsaturated organic compounds.
Electrophilic substitution. A reaction in which substitution of an atom or group atoms in organic compound with an electrophile takes place., (nitration of benzene).
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Electropositive. Describing elements that tend to lose electrons and form positive ions. The alkali metals are typical electropositive elements.
Electrorefining. The process of purifying metals by electrolysis. The impure metal is made anode and a plate of pure metal is made a cathode. The electrolyte is the aqueous solution of the metal salt.
Electrovalence number. The electrovalence number of an element is the charge (including sign) of the ion derived from the element after an electrovalent reaction. The elements of IA group will show i + electrovalence number; VII A gr. 1 - ; group IIA, +2; group VIA, 2 - .
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Element. A substance which cannot be further divided by chemical methods. The basic substances which build up chemical compounds. An element is defined by its atomic number (nuclear charge and electronic configuration).
Elements, abundance of. The relative abundance of elements depends on weather measurements are made on the crust, meteorites, core, etc. For the earth’s crust (E) abundance of the lighter elements.
Elevation of boiling point. The boiling point of a solvent is raised by the presence of a solute. For small concentrations of the solute the rise in the boiling point is proportional to the number of solute particles present in the solution. The elevation caused by 1 mole of solute in 1 litre of solvent is termed on the molecular elevation constant. (See colligative properties).
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Elimination reaction. Refers to a reaction in which a molecule decomposes to two molecules, one smaller than the other.
Elixirs. Pharmaceutical solutions frequently containing alcohol used as a sweetening or Honouring agent for drugs.
Eluent. The solvent used to separate a mixture in column chromatography
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Elution. The removal of an absorbate from an absorbent by dissolving it in a liquid (the elevent). The resulting solution is called the eluate.
Elutriation. The process of separating a material into fractions of various sizes by allowing it to settle against an upward moving stream of fluid, usually air or water.
Emanation. An obsolete name for radon.
Emerald. The grass-green variety of beryl; contains some Cr3+.
Emery. Impure a – Al2O3 (corundum) containing some iron oxide (magnetite). Used as an abrasive and polishing agent.
Emetine. C29h40N2O4. Alkaloid extracted from ipecacuanha or obtained by the methylation of cephaeline, another ipecacuanha alkaloid. A white amorphous powder, m.p. 74°C. It is a powerful emetic used against amoebic dysentery.
Empirical. Denoting a result that is obtained by experiment or observation rather than from theory.
Emulsification. The preparation of a suspension, or emulsion, of one liquid in another.
Emulsifying agent. Dilute suspensions o f oil in water behave as typical hydrophobic sols, and it is not possible to increase the concentration of oil unless a stabilizing material is added which decreases the interfacial tension. Such substances, known as emulsifying agents, are generally long – chain compounds containing a hydrophilic (carboxyl or sulphonate) group at one end of the molecule; these become orientated at the interface, the hydrophilic end projecting into the water. There re also solid emulsifying agents (e.g. carbon black which possess widely different angles of contact for two phases.
An emulsifying agent generally produces such an emulsion that the liquid in which it is most soluble forms the external phase. Thus the alkali metal soaps and hydrophilic colloids produce O/W emulsions, oil-soluble resins the W/O type.
The commonest emulsifying agents are the soaps, which have the disadvantage of coagulating in hard waters. For edible and pharmaceutical emulsions gums of various sorts are employed. Of recent years, large numbers of synthetic organic emulsifying agents have been developed.
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