Section 13.2 Factors Affecting Solvation Objectives: Describe how intermolecular forces affect solvation. Define solubility. Understand what factors affect solubility. Factors such as temperature, pressure, and polarity affect the formation of solutions.

Section 13.2 The Solvation Process Solvation is the process of surrounding solute particles with solvent particles to form a solution. This is usually called dissolving. Solvation in water is called hydration. The attraction between dipoles of a water molecule and the ions of a crystal are greater than the attraction among ions of a crystal. This intermolecular force is called an ion-dipole force.

Section 13.2 The Solvation Process (cont.) http://www.northland.cc.mn.us/biology/biology1111/animations/dissolve.html

Section 13.2 Factors That Affect Solvation Stirring or shaking moves dissolved particles away from the contact surfaces more quickly and allows new collisions to occur. Breaking the solute into small pieces increases surface area and allows more collisions to occur. As temperature increases, rate of solvation increases.

Section 13.2 Solubility The amount of grams of a substance required to form a saturated solution with 100g of solvent at a specific temperature. For example: 36 grams of NaCl in 100 grams of H2O at 20oC. Temperature must be specified Solubilities are determined experimentally Types of Solubility Unsaturated solutions are solutions that contain less dissolved solute for a given temperature and pressure than a saturated solution.

Section 13.2 Solubility (cont.) Saturated solutions contain the maximum amount of dissolved solute for a given amount of solute at a specific temperature and pressure. To identify, there is solid particles found at the bottom of the container. Solubility Curves Show how much solute will dissolve in a given amount of solvent over a range of temperatures.

Section 13.2 Solubility (cont.) Remember: Solute- the substance being dissolved Solvent- the substance doing the dissolving.

Section 13.2 Solubility (cont.) A supersaturated solution contains more dissolved solute than a saturated solution at the same temperature. To form a supersaturated solution, a saturated solution is formed at high temperature and then slowly cooled and the excess solute does not come out of solution. (It stays dissolved) Supersaturated solutions are unstable. Crystals will form eventually and a saturated solution is seen.

Section 13.2 Factors that Affect Solubility Temperature a. Temperature effects the rates at which a solute dissolves. b. Temperature has a large effect on the amounts of solute that dissolves in a given amount of solvent. c. Solubility is affected by increasing the temperature of the solvent because the kinetic energy of the particles increases

Section 13.2 Factors that Affect Solubility Solid Solubility in Liquids a. Most often  temperature,  solubility of solids Gas Solubility in Liquids a. ↑ temperature, ↓ in gas solubility

Section 13.2 Factors that Affect Solubility 2. Pressure a. Pressure has little effect on solubilities of liquids or solids in liquid solvents. b. Pressure important in gas solubilities in liquids. Solubility ↑ with ↑ pressure For example: Carbonated beverages a. Pressure slightly higher than 1 atm b. When opened, it is exposed to lower air pressure c. CO2 gas begins to bubble out of solution 1. This is called effervescence- the escape of gas from solution.

Section 13.2 Factors that Affect Solubility 3. Types of solutes and solvents a. “Like dissolves Like” rule 1. “Likeness” depends on: a. Type of bonding b. Polarity of Molecules c. Type of intermolecular forces found in the two mixed substances

Section 13.2 Factors that Affect Solubility b. Possible combinations 1. Polar dissolves in Polar 2. Nonpolar dissolves in Nonpolar 3. Ionic compound dissolves in Polar

Section 13.2 Factors that Affect Solubility (cont.) Sucrose molecules have several O–H bonds, which become sites for hydrogen bonding with water molecules. Oil does not form a solution with water because there is little attraction between polar water molecules and nonpolar oil molecules.

Section 13.2 Factors that Affect Solubility Why Do Some Things Dissolve? Solubility of a substance is based on the idea of attraction between particles and the type of particle involved. Dissolving is due to intermolecular forces.

Section 13.2 Factors that Affect Solubility How can you determine what dissolves in what? Predict whether the substances are ionic, polar covalent, or nonpolar covalent. (Use prior knowledge) 2. Then compare type of substances using the rule “Like dissolves Like”. -polar dissolves polar -ionic dissolves polar -nonpolar dissolves nonpolar