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

2 Physical properties of liquidsVapor 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

3 Physical properties of liquidsBoling 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

4 Introduction to colligative propertiesSince 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

5 Colligative Properties of SolutionsAre 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

6 Colligative PropertiesWhy 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

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

8 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 = X2 Fraction molar X1 + X2 = 1 P1 = ( X2 ) P10 P P1 = X2 P10 ΔP = X2 P10 Ciencias de la Tierra II

9 Elevation of the boiling pointΔ 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

10 Decrease in the freezing pointΔ 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

11 Increase in the osmotic pressureThe 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

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

13 Ciencias de la Tierra IIAvoid 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

14 Ciencias de la Tierra IIConservation 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

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

16 Ciencias de la Tierra IIPeople 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

17 Ciencias de la Tierra IIBibliography 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 from the World Wide Web: : Ciencias de la Tierra II