What are Solutions? Section 15.1 Objectives:

Review 1.What are intermolecular forces? 2.Name 3 types of intermolecular forces. 3.What is the strongest type of intermolecular force?

Solvation in Aqueous Solutions Intermolecular (attractive) forces hold together particles in solutes and in solvents. These forces also exist between particles in the solute and particles in the solvent. What do you think must occur for a solid to dissolve into solution? Answer: The attractive forces between solute and solvent particles must be stronger than those between the solute particles, separating the solute particles.

Solvation in Aqueous Solutions, continued……… Solvation: the process of solute particles being surrounded by solvent particles Hydration: solvation in water What type of compound is NaCl? Answer: Ionic When NaCl is surrounded by partially charged, polar water molecules, the attractive forces pull ions off the salt crystal in solution.

Solvation in Aqueous Solutions, continued……… Sugar (sucrose) is a molecular compound. What does this mean? Answer: It is formed by covalent bonds, not ionic. However, sugar has –OH bonds, which will form hydrogen bonds with polar water molecules. How does this explain how sugar dissolves? Answer: The hydrogen bonds are strong enough to pull apart (separate) the sucrose molecules.

Solvation in Aqueous Solutions, continued……… Oil is also a molecular compound, but it is made up of mainly carbon and hydrogen (- CH) bonds. Why do you think oil is immiscible in water? Answer: The nonpolar oil molecules are not attracted to the polar water molecules. Application: Soap (nonpolar) attracts nonpolar grease and oil in clothing.

Rate of Solvation Name three things that would affect the rate of solvation: 1.Agitating the mixture 2.Increasing the surface area of the solute 3.Raising the temperature of the solvent

Assignment: Complete the table Factors that Affect the Rate of Solvation Using Kinetic- Molecular Theory, explain HOW the factor affects the rate of solvation Give an example of this factor at work

Heat of Solution Review: Define – Endothermic process – Exothermic process All solvation processes contain both endothermic and exothermic steps. The separation of particles in the solute and the solvent requires energy to overcome the attractive forces (endothermic).

Heat of Solution, continued… The attractive forces between the solute and solvent particles releases energy (exothermic). The overall energy change --- the heat of solution --- may be either exothermic OR endothermic. Give an example of each type of reaction. Discovery Lab: CaCl 2 – endothermic; NH 4 Cl - exothermic