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Вы можете ознакомиться и скачать презентацию на тему Colloid chemistry. Доклад-сообщение содержит 55 слайдов. Презентации для любого класса можно скачать бесплатно. Если материал и наш сайт презентаций Mypresentation Вам понравились – поделитесь им с друзьями с помощью социальных кнопок и добавьте в закладки в своем браузере.

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Rule Paneth-Fajans Determine the sign of the surface charge of AgI (cryst.) obtained by the reaction: АgNО3(s) + КI(s) = АgI(cryst.) + KNO3(s) а) nАgNО3 = nКI : surface sediment is not charged; б) nАgNO3 > nКI : в) nАgNО3 < nКI : excess АgNO3  Аg+ + NО3- excess КI  К+ + I- АgI + АgI - + - + -

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Molecular-kinetic properties of dispersion systems

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Brownian motion Colloidal particles by molecular-kinetic properties are not fundamentally different from true solutions. Weighted particles in the solution are in constant random thermal motion.

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Brownian motion The collision of particles is an exchange of energy and as a result the average kinetic energy is set, same for all particles.

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Diffusion Diffusion - spontaneous process of alignment of particle concentration throughout the volume of solution or gas under the influence of thermal motion. Einstein studied the Brownian motion, he established the diffusion coefficient - D connection with an average shift:

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The osmotic pressure Osmotic pressure in colloidal systems is a very small amount, it is difficult reproducible experiments. Osmotic pressure in colloidal systems is inversely proportional to the cube of the particle radius:

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Sedimentation Sedimentation (from Lat. Sedimentum - sediment) is the process of sedimentation of dispersed particles in a liquid or gaseous medium under the influence of gravity. Emergence of particles is called reverse sedimentation. Sedimentation rate of the particles obeys the law Stokes :

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Sedimentation analysis For sedimentation analysis of kinetically stable systems to determine the size and mass of the particles is not enough force gravity. Russian scientist AV Dumanskiy (1912) proposed to expose colloidal systems centrifugation. Swedberg (1923) developed a special centrifuge with great speed, called the ultracentrifuge.

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Ultracentrifugation Modern ultracentrifugation allow to obtain a centrifugal force in excess of the acceleration of gravity 105. Modern ultracentrifuge - complex apparatus central part rotor of which (with speed 20-60000 rev / min and up).

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Optical properties of disperse systems

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The scattering of light This is the most characteristic optical property of colloidal systems. The light is scattered in all directions. This phenomenon was observed Faraday (1857) in the study of gold sol. The phenomenon Tyndall in 1868. Through pure liquids and molecular solutions light just passes. Through colloidal dispersions light ray meeting on the way a particle is not reflected, as if it skirts, and rejected several changes its direction (diffraction).

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The scattering of light Tyndall found that when illuminated colloidal solution bright light ray path it is visible when viewed side as a luminous cone - Tyndall cone.

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Electrical properties of disperse systems

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DEL. Formation of a double electric layer DEL existence of ions and the potential jump at the interface of the two phases plays an important role in many phenomena important for theory and practice . These include: the electrode processes , electrocapillary and electrokinetic phenomena , phenomena associated with the electrostatic interaction of colloidal particles , largely determine the stability of the dispersed system . All these phenomena are interconnected through DEL , called Electrosurface . There are three possible mechanisms for the formation of DEL : Due to the transition of electrons or ions from one phase to another ( 1st variant ); As a result of the selective adsorption of ions in the electrolyte interphase layer ( 2nd variant ); As a result of the orientation of the polar molecules conjugated phases in their interaction ( third variant ) .

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When immersed in water, the metal plate portion of the positive ions, which are located in the crystal lattice as a result of interaction with the dipoles of water will go into solution. When immersed in water, the metal plate portion of the positive ions, which are located in the crystal lattice as a result of interaction with the dipoles of water will go into solution.

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Electric double layer 2nd version. In the formation of AgI sol by reaction between AgNO3 and KI at AgI microcrystals adsorbed ions (Ag +, I-). If an excess of silver nitrate, the silver ions are adsorbed. When this solid phase is positively charged (variant b). Excess anions NO3-ions are attracted to the Ag +

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Electric double layer third variant. When the orientation of polar molecules at the interface in the presence of metal ions. At the same potential-anions are polar (example) fatty acids

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The structure of DEL. First picture of DEL was expressed Kwinke (1859) and developed in the works of Helmholtz (1879). DEL theory was developed in the works of scientists of the USSR A.N. Frumkin and B.V. Deryagin. The first theory was the theory of the structure of DEL Helmholtz: DEL consists of two flat charges located at the molecular distance from one another and interact with each other only by electrostatic forces of attraction.

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Structure of DEL Gouy-Chapman model assumed location counterions diffusion under the influence of forces acting in opposite directions: the electrostatic forces of attraction to the surface and forces the thermal motion of the ions.

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Structure of DEL According to modern concepts (Stern’s theory) structure of DEL: ions are included in the solid phase, form the inner lining of the double layer, ions of opposite sign, i.e. counterions forming an outer lining, wherein the counterions part is in direct contact with ions of the solid phase, forming a dense layer, and another part is counterions diffused layer.