COLLOIDAL SOLUTIONS. Department of Medical Chemistry Pomeranian Medical University

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1 COLLOIDAL SOLUTIONS Department of Medical Chemistry Pomeranian Medical University 1

2 COMPONENTS OF THE SYSTEM -chemicals which create the system. They create different type of mixtures - which makes the system to exists in various phases. PHASE part of the system is separated from other phases with distinct border where sudden change in physico-chemical changes takes place. Phase containing one component pure substance Phase containing more than one component - solution SOLUTION mixture of two or more components dissolved in solvent (solvent-subtance in quantitative excess over other componet) 2

3 Systems can be divided due to: 1) number of components: one-component multicomponent 2) number of phases : single phase multiple phase SYSTEMS: SYSTEMS HETEROGENOUS multiplephase (seemingly single-phase), heterogeneous; eg. water with ice (heterogeneous, two-phase, singlecomponent system ), water with mercury (heterogeneous, two-phase, twocomponent system ) HOMOGENOUS single-phase, homogeneous throughout the volume, both chemically and physically; e.g. glucose solution (homogeneous single phase, two components system) 3

4 Types of solutions depending on size of dispersed phase in dispersive medium TYPE OF SOLUTION True solution (homogeneous) Colloidal (heterogeneous) DIAMETER OF PARTICLES OF DISPERSED PHASE < 10-9 m (<1nm) m (1-100 nm) Suspension > 10-7 m (>100 nm) 4

5 COLLOIDAL SOLUTIONS COLLOIDAL SOLUTIONS heterogenous dispersive system with distinguished continuous scattering phase (solvent)) and discontinuous dispersed phase with particle diameter of m (1 100 nm, up to 500nm) All living cells are sets of various colloidal systems. Colloidal systems are widespread : in animate nature (proteins, carbohydrates) in inanimate nature (clay, fog, volcanic dust) synthetic materials (soap, colorants, colloidal sulphur, metal oxides) 5

6 COLLOIDAL SOLUTION HETEROGENEOUS system - with particle size of m in diameter (1 100 nm, up to 500 nm) COLLOIDAL SOLUTIONS 10-9 m = 1 nm = micron 10-7 m = 100 nm = 0.1 micron 10-6 m = 1000 nm = 1 micron 6

7 Properties of colloids (1): 1. They can be seen in ultra microscope. Attention: the difference between an ultra-microscope and ordinary one is that in the former the light falls laterally on the liquid under study, instead of from below. The ordinary microscope with x400 magnifications has limitations for particles below 1 micron, but it is still able to show general structures of colloid system. 2. They are not dialyzed > Colloidal particles will not be separated by membranes (like bladder or parchment paper), because they will not diffuse through a membrane. 3. They show permanent Brownian motions mostly particles smaller than 100nm are able to do strong Brownian motion. 4. They show Tyndall effect visible light scattering by the colloidal particles. 5. They may coagulate > colloid particles become agglomerated. 7

8 Tyndall Effect This is light scattering by colloidal solution (for example by dust, fog, milk,etc.). When light beam passes through the colloidal dispersion it is scattered and therefore is visible. When light beam passes through the solution, like glucose dissolved in water, it is not scattered and therefore it cannot be seen. Intensity of this phenomena is larger when difference between light scattering of dispersive medium is larger then light scattering of dispersed phase. 8

9 Solutions vs Colloids The Tyndall Effect True Solution e.g. water + glucose Colloidal mixture, e.g. milk 9

10 The Tyndall Effect 10

11 CLASSIFICATION OF COLLOIDAL SYSTEMS DEPENDING ON : I. STATE OF DISPERSING AND DISPERSED PHASE Disperssed phase Disperssing phase COLLOID EXAMPLE Gas Gas - - Liquid Gas Aerosol liquid Fog, clouds, vapors Solid Gas Aerosol solid Smoke, dust Gas Liquid Foam Foam: soap, beer Liquid Liquid Emulsion Creams, nail polish, milk, mayonese, butter Solid Liquid Sol Polymer solutions Gas Solid Foam Pumice, styrofoam Liquid Solid Emulsion solid Gels, opal Solid Solid Sol solid Glass rubin, colour cristals 11

12 CLASSIFICATION OF COLLOIDAL SYSTEM : II. III. Size of colloidal particles: monodispersive (particles of dispersed phase have the same dimensions) polydispersive (particles of dispersed phase have different dimensions) Affinity of dispersed phase to dispersing medium : liophilic colloids they have large affinity to solvent particles; colloidal particles are surrounded by solvent particles liophobic colloids they have small affinity to solvent and adsorb on the surface of particles large quantities of one type of ions 12

13 CLASSIFICATION OF COLLOIDAL SYSTEM DEPENDS ON (cont.) IV. Quality of dispersed phase: Emulsions the dispersed phase is of nonpolar character (e.g. lipids) and does not have affinity to dispersion medium (e.g. water). Emulsions have hydrophobic character and are also called suspensions or irreversible colloids. In living organisms example of emulssions are lipids. Small particles of lipids can be dispersed in water thanks to the compounds called emulsifiers. Emulsifier this is compund which can be dissolved in both dispersed phase and dispersion medium. For example, consumed fats are emulsified by bile acids contained in bile. They have ability to decrease surface tension, like soap in water. 13

14 AgI micelle structure precipitated with excess of KI DIFFUSION LAYER nucleus Nucleus of colloidal molecule +adsorbtion layer core micelle 14

15 COLLOIDS STRUCTURE Hydrophobic micell are mostly built by oxides, sulphates, hydroxides of heavy metals Hydrophilic colloids are built usually by large molecules such as : proteins. Their stability is due to the presence of water molecules adsorbed on their surface. 15

16 Coagulation (1) COAGULATION it is an ability of colloid particles to combine with each other and form larger structures called agregates. After reaching appropriate size they loose ability to flow and they sediment on the bottom. Coagulation can be caused by: 1. radioactivity beta ray 2. heating coagulation of protein (egg) 3. evaporation or freezing of dispersive medium 4. dehydration, for example by using acetone, alcohol 5. addition of electrolite to colloid 16

17 Coagulation (2) Peptization process opposite to coagulation breaking coagulate and return from coagulate to colloid. SOL coagulation GEL peptization 17

18 Coagulation (3) Hydrophilic colloid (reversible) takes place when water coat has been removed Hydrophobic colloids (irreversible) takes palce when electrical charge present on the surface becomes neutralized. 18

19 HYDROPHOBIC COLLOIDS HYDROPHILIC Salts with multivalance cations Strongly hydrated salts coagulate Water particles 19

Coagulation (4) Conditions for salting out of protein Proteins are easiest to be salted out in their isoelectric point (pi) because they do not posses any electrical charge, they attract themselves

20 Coagulation (4) Conditions for salting out of protein Proteins are easiest to be salted out in their isoelectric point (pi) because they do not posses any electrical charge, they attract themselves strongly and create aggregates, which leads to precipitation (lack of electrical charge helps molecules to aggregate, which allows them to precipitate from solution). In ph different from pi, protein due to presence of the surface charge can exist in solution despite not having water coat ( they behave similar as hydrophobic colloids) Addition of small amount of neutralizing electrical charge ions leads to protein precipitation. Such protein does not posses either electrical charge or water coat. 20

21 dyhadration Conditions for salting out protein from solution Protein ion Protein in pi Protein cation Base addition ph increase Acid addition ph decrease Charge lost due to cation addition charge lost due to anion addition Protein anion precipitate Protein cation suspenoid 21

22 Salting out of proteins Proteins are easy to salt-out in isoelectric point (pi) and in this state they easily sediment as larger aggregates. [Isoelctric point it is ph at which proteins have no electric charge]. In ph different than pi protein can exist in solution despite having no hydrophilic coat. html 22

23 PROTECTIVE ROLE OF HYDRPHILIC COLLOIDS ON HYDROPHOBIC COLLOIDS Hydrophilic colloids show higher stability than hydrophobic colloids, because of two stabilizing factors: hydration layer sometimes - particles have the same charge (which can be result of dissotiation of acidic or basic groups being present in colloidal particle) Hydrophilic colloids are acting protective on hydrophobic colloids addition of hydrophilic colloid to hydrophobic is causing creation of stable system from which it is difficult to precipitae suspended particles (e.g. small amount of protein added to colloidal gold suspension protects it from coagulation). Protective role of colloid can be determined quantitatively by providing gold number ( gold number it is the smallest amount of miligrams of protective colloid in respect to pure substance which is able to protect 10cm 3 0,1% of formaldehyde gold sol, against color change from red to purple after addition of 1cm 3 10% NaCl ) 23

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COLLOIDAL SOLUTIONS. Department of Medical Chemistry Pomeranian Medical University

COLLOIDAL SOLUTIONS. Department of Medical Chemistry Pomeranian Medical University COLLOIDAL SOLUTIONS Department of Medical Chemistry Pomeranian Medical University 1 COMPONENTS OF THE SYSTEM -chemicals which create the system. They create different type of mixtures - which makes the