Colligative Properties of Solutions (Session 19) Ciencias de la Tierra II

Physical properties of liquids Vapor Pressure: is the pressure of vapor measured in a dynamic equilibrium of evaporation-condensation exerted by a liquid when it is found in a closed container. Chang, R. (1992) Ciencias de la Tierra II

Physical properties of liquids Boling Point: temperature in which the vapor pressure of a liquid is equal to the exterior atmospheric pressure. Freezing Point: temperature in which the equilibrium phases solid and liquid coexist. Ciencias de la Tierra II

Introduction to colligative properties Since solutions are mixtures, the properties of the solutions depend on the amount of substances that form the solution. Some of the physical properties of the solutions depend solely on the concentration of particles in the solution, without considering its particles. These properties are know as colligative properties of the solutions. Ciencias de la Tierra II

Colligative Properties of Solutions Are the physical properties of the solutions that depend on the amount but not on the type of solute particles. (Non volatile solutes). These are 4 factors that affect the Colligative properties Decrease of vapor pressure. Increase of the boiling point. Decrease of the freezing point. Increase in osmotic pressure. Ciencias de la Tierra II

Colligative Properties Why do these changes in the physical properties happen? Explain how you…. Decrease the vapor pressure. Elevate the boiling point. Decrease the freezing point. Increase the osmotic pressure. Ciencias de la Tierra II

Decrease of Vapor pressure The degree in which a nonvolatile solute reduces the steam pressure in proportion to its concentration NaCl 8% Ciencias de la Tierra II

Decrease of Vapor pressure using the solutions “Raoult Law” Raoult Law establishes that the partial pressure that a dissolvent exerts on a dissolution, P1 , is given by the vapor pressure of the pure dissolvent, P10 , multiplied by the molar fraction of the dissolvent in a dissolution, X1: P1 = X1 P10 if X1 = 1 - X2 Fraction molar X1 + X2 = 1 P1 = ( 1 - X2 ) P10 P10 - P1 = X2 P10 ΔP = X2 P10 Ciencias de la Tierra II

Elevation of the boiling point Δ T =Tb -Tb0 Tb -Tb0 = Kb * m Where: Kb is a molal constant of the boiling point elevationof a pure dissolvent. m is the molal concentration. Ciencias de la Tierra II

Decrease in the freezing point Δ Tf =Tf0 -Tf Tf0 -Tf = Kf * m Where: Kf is the molal constant mole the freezing point depression of a pure dissolvent. m is molality. Tf0 is the freezing point of the pure solvent Tf is the freezing point of the solution Ciencias de la Tierra II

Increase in the osmotic pressure The osmotic pressure of the dissolutions is calculated with the following formula: π = Osmotic Pressure = M R T Where: M is molarity R the general constant of gases T Kelvin temperature Ciencias de la Tierra II

Applications of colligative properties of solutions in daily life Conservation of fruits and vegetables Conserves and pickles Ciencias de la Tierra II

Ciencias de la Tierra II Avoid the formation of ice on roads when the temperature is very low in winter adding CaCl2 to ice which dissolves the ice and forms a barrier. Ciencias de la Tierra II

Ciencias de la Tierra II Conservation of fishing products in salt water. Fish arefrozen in a temperature below the freezing point of water without freezing the product and it is free of any actions by microorganisms. Ciencias de la Tierra II

Ciencias de la Tierra II Avoid water evaporation in the radiators of cars adding ethylene. Ciencias de la Tierra II

Ciencias de la Tierra II People that require replacement of corporal fluids or nutrients, like blood, glucose, vitamins, minerals, etc. These solutions must be isotonic in respect to our fluids. Ciencias de la Tierra II

Ciencias de la Tierra II Bibliography Brown, T. et al. (1991) Chemistry: The Central Science. 5th ed. Untied States of America: Prentice Hall. Burns, R. (1996) Chemistry Fundaments. 2nd. ed. United States of America: Prentice Hall. Chang, R. (1992). Chemistry. 4th ed. United States of America: McGraw Hill. Cypher International Ltd. (2001). Project Portfolio “Image|. Cypher International Ltd. Extracted on May 19 2003 from the World Wide Web: : http://www.cypherltd.com/0414.html Ciencias de la Tierra II