Colloidal systems. Classes of solution True solutions Colloids Suspensions Homogenous mixture when 2 or more substances are dissolved together Contain. - презентация

1 Colloidal systems

2 Classes of solution True solutions Colloids Suspensions Homogenous mixture when 2 or more substances are dissolved together Contain particles that are in the middle in size. They dont separate into layers. Fog is a colloid. Property of colloid is scattering of light. Heterogeneous mixture. It dissolves over time( solid particles that are sufficiently large for sedimentation. sedimentation

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6 Structure of colloidal particles(micells) A colloidal particle does not have a definite composition, therefore its structure can be represented only schematically. Consider the structure of a colloidal micelle using the example of the silver iodide hydrosol obtained by the interaction of dilute solutions of silver nitrate and potassium iodide: AgNO3 + KI -> AgI + KNO3 {[AgI] m · nI – · (n-x)K + } x– · x K + {[AgI] m · nAg + · (n-x)NO 3 – } x+ · x NO 3 –

7 Physical properties of colloids

8 Heterogeneity: Colloidal solution consists of dispersed phase and dispersion medium. Visibility of particles: The dispersed particles present in colloid are not visible to the naked eye and can seem homogenous. Filterability: The colloidal particles may pass through filter paper without being separated from medium, however can be retained by membranes Stability: Lyophilic sols in general and lyophobic sols in absence of substantial concentration are quite stable.

9 Optical properties of colloids

10 Mechanical properties of colloids

11 Electrical properties

12 Electrical properties: Electroosmosis

13 Coagulation of colloids Coagulation is a process which involves coming together of colloidal particles so as to change into large sized particles which ultimately settle as a precipitate or float on the surface. Coagulation is generally brought about by the addition of electrolytes. When an electrolyte is added to a colloidal solution, the particles of the sol take up the ions which are oppositely charged and thus get neutralized. The neutral particles then start accumulating to form particles of a larger size which settle down.

14 Hardy Schulze law: The quantity of the electrolyte which is required to coagulate a definite amount of a colloidal solution depends upon the valency of the ion having a charge opposite to that of the colloidal particles. It can be defined as: Greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation.

15 Biological significance of colloidal systems Cytoplasm has colloidal nature Blood-high plasma protein makes a colloidal system. This system maintains pH and osmotic concentration of blood. Fruits also exhibit colloid properties

16 Colloid advantages

17 Colloids in medicine

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19 Bibliography loids_6.htm loids_6.htm colloidal-solutions/ colloidal-solutions/ ii/ ii/