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Solutions A solution is formed when a substance is dissolved in a solvent. Any solution is formed of 2 phases; the solute which is also called dispersed phase and solvent which is also called dispersion phase Types of solutions Solutions can be classified according to the concentration or the size of solute particles A- According to the concentration of solute particles, solutions may be: 1- Normal solution It is a solution, which contains the equivalent weight of the solute in grams dissolved in one liter of the solution. 2-Molar solution It is a solution, which contains the molecular weight of the solute in grams dissolved in one liter of the solution. 3-Molal solution It is a solution, which contains the molecular weight of the solute in grams dissolved in one kilogram of the solvent. B- According to the size of solute particles, solutions may be: 1- Crystalloids (True solutions) They are solutions in which the size of solute particles is less than 1 mµ (millimicron) e.g. sodium chloride solution. 2- Colloids These are solutions in which the size of solute particles ranges from 1 to 100 mµ. e.g. plasma proteins 3- Suspensions They are solutions in which the size of solute particles is more than 100 mµ e.g. suspension of sand in water. Colloids These are solutions in which the size of solute particles ranges from 1 to 100 mµ. e.g. plasma proteins. Types of colloids According to their ability to take up the solvent, colloids are classified into emulsoids and suspensoids 1- Emulsoids They are lyophilic (solvent loving) colloids. If the solvent is water they are called hydrophilic colloids. They are more viscid. They are more stable and not easily precipitated as the solute particles are surrounded by 2 stability factors: 1 i- Negative or positive charge. ii- A shell (layer) of solvent. They can be precipitated by dehydration followed by neutralization of 2 the charge. charg Examples for emulsoids include protein, starch and egg white a layer of solvent solutions. 2- Suspensoids They are lyophobic (solvent hating) colloids. If the solvent is water they are called hydrophobic colloids. They are less viscid than emulsoids. They are less stable and easily precipitated as the solute particles are surrounded by one stability factor that is negative or positive charge. They can be precipitated by neutralization of the charge. Examples for emulsoids include colloidal gold and colloidal iron solutions. The charge on the colloidal particles may be due to 1- Ionization of some groups on the surface of colloidal particles. 2- Ions from the solvent may be adsorbed on the surface of the colloidal particles. Stability factors of colloids 1- Presence of negative or positive charge on the surface of the colloidal particles. 2- Presence of a shell (layer) of solvent surrounding the particles of emulsions. 3- The size of colloidal particles; the smaller the size, the more stable the colloid. Separation of colloids 1- Ultracentrifugation, which means centrifugation of the solution at a very high speed. 2- Ultrafiltration, which means forcing the solution, under pressure, through membranes of varying porosity. 3- Electrophoresis, which means migration of colloidal particles in electric field. Precipitation of colloids Colloids can be precipitated by: 1- Dehydrating agents. 2- Strong agitation, freezing and heating. 3- Colloids of opposite charge. Viscosity Viscosity means the resistance offered by a fluid to flow. It is reported in units called poise It is measured by comparing the time needed for certain amount of the fluid to flow through capillary tube at a definite temperature, with the time which is taken by an equal volume of water to flow through the same capillary tube at the same temperature. Factors affecting viscosity 1- Temperature, viscosity decreases with the rise of temperature. 2- Solute concentration, viscosity increases with the increase in solute concentration. 3- Size of particles of the solute, viscosity increases with the increase in the size of particles. 3 Diffusion Diffusion means passage of substances in the solution in which they are suspended. It occurs in many fluids of the body within cells during secretory activity. Water Copper sulphate solution Water Prussian blue solution Diffusion of copper sulphate and prussian blue Factors affecting diffusion 1- Size of particles, diffusion decreases with the increase in the size of particles. 2- temperature, diffusion increases with the increase in temperature. An example of diffusion is the diffusion of copper sulphate and prussian blue in water. Copper sulphate diffuses in water more rapidly than prussian blue does because copper sulphate has smaller particle size. Dialysis Dialysis means separation of colloids from crystalloids using a semipermeable membrane, crystalloids can pass this membrane but colloids can not because of the large size of their particles. Dialysis is used in cases of renal failure. Blood passes through dialyzing machine to get red of waste products (as urea and creatinine), which are crystalloids, and preserving plasma proteins, which are colloids. Surface Tension It is the force of attraction between molecules in liquids that holds the surface molecules of a liquid together and attracts them towards the body of the liquid. It is caused by unequal attraction of the surface molecules by the inside molecules. Below the surface of the liquid, the force of cohesion (sticking together) between molecules is the same in all directions. Molecules on the surface of the liquid, however, are subjected to a net unbalanced force of attraction that pulls them towards the body of the liquid. As a result, the liquid tries to take on the shape that has the smallest possible surface area (the shape of a sphere). Salt solutions have higher surface tension than organic solutions. Surface tension decreases with the increase in temperature. Surfactants are substances that lower surface tension. They include soaps, bile salts and phospholipids . Hydrotropy It is the capacity of certain substance to make water insoluble substances more soluble in water. Hydrotropic factors are substances, which make water insoluble substances more soluble in water. Examples of hydrotropic factors include bile salts, phospholipids and glucuronic acid. Adsorption It is the capacity of substance to make other substance closely attached to its surface (adsorbed on it) due to presence of attractive forces on its surface. Examples of adsorbents include charcoal, kaolin, talc powder and zinc oxide. Importance of adsorbents 1- Charcoal tablets are used to adsorb gases in the intestine in gastric distention. 2- Kaolin is used in treatment of diarrhea as it adsorbs bacteria and their toxins. Elution Elution means recovery of adsorbed material from adsorbing agent. The solvent used in elution is called eluent and the extract obtained from elution is called eluate. Chromatography is a technique that depends upon adsorption followed by elution. It is used for separation and purification of important compounds such as many hormones, enzymes, neurotransmitters, peptides and amino acids. 4