Solutions, Colloids and Suspensions

Solutions Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed uniformly throughout the solvent.

Solutions Have small particles (ions or molecules) Are transparent Do not separate Cannot be filtered Do not scatter light.

Types of Solutions Saturated:  Solvent holds as much solute as is possible at that temperature. Unsaturated:  Less than the maximum amount of solute for that temperature is dissolved in the solvent. Supersaturated:  Solvent holds more solute than is normally possible at that temperature.

Ways of Expressing Concentrations of Solutions

Mass Percentage Mass % of A = mass of A in solution total mass of solution  100 Percent (by mass) = g solute g solution x 100 g solute g solute + g solvent x 100 =

% (w/w) = % (w/v) = % (v/v) = % Concentration

Parts per Million and Parts per Billion ppm = mass of A in solution total mass of solution  10 6 (  g/g, mg/L) Parts per Million (ppm) (  g/g, mg/L) (ng/g,  g/L) Parts per Billion (ppb) (ng/g,  g/L) ppb = mass of A in solution total mass of solution  10 9

The units ppm or ppb are used to express trace concentrations. These are weigh or volume based, rather than mole based. The units ppm or ppb are used to express trace concentrations. These are weigh or volume based, rather than mole based.

Colloids Have medium size particles Cannot be filtered Separated with semipermeable membranes Scatter light (Tyndall effect)

The scattering of visible light by colloidal particles is called the Tyndall effect.

Colloids in Biological Systems Some molecules have a polar, hydrophilic (water-loving) end and a nonpolar, hydrophobic (water- hating) end.

Colloids in Biological Systems Sodium stearate is one example of such a molecule. These molecules can aid in the emulsification of fats and oils in aqueous solutions.

Suspensions Have very large particles Settle out Can be filtered Must stir to stay suspended

Examples of Suspensions Blood platelets Muddy water Calamine lotion

Osmosis and Dialysis

Osmosis and Osmotic Pressure ►Osmosis: The passage of solvent through a semipermeable membrane separating two solutions of different concentration. ►Osmotic pressure: The amount of external pressure applied to the more concentrated solution to halt the passage of solvent molecules across a semipermeable membrane.

Osmosis semipermeable membrane 4% starch10% starch H2OH2O

Equilibrium is reached. water flow becomes equal 7% starch H2OOH2OO

Osmotic Pressure Produced by the number of solute particles dissolved in a solution Equal to the pressure that would prevent the flow of additional water into the more concentrated solution Increases as the number of dissolved particles increase.

Osmotic Pressure of the Blood Cell walls are semipermeable membranes The osmotic pressure of blood cells cannot change or damage occurs. The flow of water between a red blood cell and its surrounding environment must be equal.

24 Isotonic solutions Exert the same osmotic pressure as red blood cells. Medically 5% glucose and 0.9% NaCl are used their solute concentrations provide an osmotic pressure equal to that of red blood cells H2OH2O

Hypotonic Solutions Lower osmotic pressure than red blood cells Lower concentration of particles than RBCs In a hypotonic solution, water flows into the RBC The RBC undergoes hemolysis; it swells and may burst. H 2 O

Hypertonic Solutions Has higher osmotic pressure than RBC Has a higher particle concentration In hypertonic solutions, water flows out of the RBC The RBC shrinks in size (crenation) H2OH2O

Dialysis Occurs when solvent and small solute particles pass through a semipermeable membrane Large particles retained inside Hemodialysis is used medically (artificial kidney) to remove waste particles such as urea from blood.

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