Chapter 12 • Section 1 – Types of Mixtures • Section 2 – The Solution Process • Section 3 – Concentration of Solutions
12.1 - Types of Mixtures • Distinguish between electrolytes and nonelectrolytes. • List three different solute-solvent combinations. • Compare the properties of suspensions, colloids, and solutions. • Distinguish between electrolytes and nonelectrolytes.
Definitions • Soluble: capable of being dissolved What is something that is soluble? • Solution: homogeneous mixture of two or more substances in a single phase Review: What is a homogeneous mixture?
Definitions Cont. • Solvent: substance doing the dissolving • Solute: substance dissolved in solution • Can be any combination of solid, liquid, or gas • A solid solution is called an alloy • Example: brass is zinc and copper
Examples In these examples, the substance with the greater volume is the solvent
Suspensions • Suspension: particles in a solvent are so large they settle out unless the mixture is constantly stirred What is an example of a suspension?
Colloids • Colloid: particles that are intermediate in size between those in solutions and suspensions the particles are small enough to be suspended throughout the solvent by the constant movement of the surrounding molecules • Colloidal particles make up the dispersed phase, and water is the dispersing medium. • Example: mayonnaise
Tyndall Effect • Tydnall Effect: when light is scattered by colloidal particles dispersed in a transparent medium • This is used to distinguish between a solution and a colloid • Remember the Types of Solutions Lab from the beginning of the year?
Emulsions a mixture of two or more immiscible (un-blendable) liquids
Electrolytes • Electrolyte: a substance that dissolves in water to give a solution that conducts electric current • What would make a good electrolyte – ionic or covalent compounds? Why? • Ionic – the positive and negative ions separate from each other in solution and are free to move making it possible for an electric current to pass through the solution
Nonelectrolyte • Nonelectrolyte: a substance that dissolves in water to give a solution that does not conduct electricity • Neutral solute molecules do not contain mobile charged particles so they do not conduct electric current • Example: sugar
12.2 - The Solution Process Listand explain three factors that affect the rate at which a solid solute dissolves in a liquid solvent. Explainsolution equilibrium, and distinguish among saturated, unsaturated, and supersaturated solutions. Explainthe meaning of “like dissolves like” in terms of polar and nonpolar substances. Listthe three interactions that contribute to the enthalpy of a solution, and explain how they combine to cause dissolution to be exothermic or endothermic. Comparethe effects of temperature and pressure on solubility.
Factors Affecting the Rate of Dissolution 1. Increase the surface area -- because dissolution occurs at the surface 2. Stirring or shaking -- increases contact between solvent and solute 3. Increase the temperature -- increases collisions between solute and solvent and are of higher energy
Solubility • If you add spoonful after spoonful of sugar to tea, eventually no more sugar will dissolve. • There is a limit to the amount of solute that can dissolve in a solvent. • The limit depends on: • Solute • Solvent • Temperature
Solubility Cont. • When a solute is added, the molecules leave the solid surface and move about at random. • As more solute is added, more collisions occur between dissolved solute particles. Some of the solute molecules return to the crystal. • When maximum solubility is reached molecules are returning to the solid form at the same rate they are going into solution (much like the vapor pressure of a liquid) • This is called solution equilibrium
Solutions • Saturated Solution: contains the maximum amount of dissolved solute • Supersaturated Solution: contains more dissolved solute than a saturated solution • Unsaturated Solution: contains less solute than a saturated solution under the same condition
Solutions Cont. • When a saturated solution is cooled, the excess solute usually comes out of solution, leaving the solution saturated at the lower temperature. • A supersaturated solution will form crystals of solute if disturbed or more solute is added.
Solubility Values • Solubility: the amount of substance required to form a saturated solution with a specific amount of solvent at a specified temperature • Example: solubility of sugar is 204 g per 100 g of water at 20OC • Solubilities vary widely and must be determined experimentally
Solute-Solvent Interactions • Solubility depends on the compounds involved. • “LIKE DISSOLVES LIKE” is used to predict whether one substance will dissolve in another • What makes substances similar depends on: • Type of bond • Polar/Nonpolar molecules • Intermolecular forces
Dissolving Ionic Compounds in Aqueous Solutions • What type of forces are present in water? • These forces attract the ions in ionic compounds and surround them, separating them from the crystal surface and drawing them into solution. • Hydration: when water is the solvent • Ions are said to be hydrated
Nonpolar Solvents • Ionic compounds are generally not soluble in nonpolar solvents • Example: carbon tetrachloride, CCl4 toluene, C6H5CH3 • The nonpolar solvent does not attract the ions to break apart the forces holding the crystal together. • There are differences in: __________ , ___________ , __________
Liquid Solutes and Solvents • Oil and water do not mix because oil is nonpolar and water is polar. The hydrogen bonding squeezes out whatever oil molecules may come between them. • Two polar substances or two nonpolar substances easily form solutions. • Immiscible: liquids that are not soluble in each other • Miscible: liquids that dissolve freely in one another in proportion
Pressure and Solubility • Increases in pressure, increase gas solubilities in liquids • An equilibrium is established between a gas above a liquid solvent and the gas dissolved in a liquid
Pressure and Solubility Cont. • Increasing the pressure… causes gas particles to collide with the liquid surface and forces more gas into the solution • Decreasing the pressure… allows more dissolved gas to escape from solution
Henry’s Law • Henry’s Law: solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid • In carbonated beverages, the solubility of carbon dioxide is increased by increasing the pressure. The sealed containers contain CO2 at high pressure, which keeps the CO2 dissolved in the beverage, above the liquid. • When the beverage container is opened, the pressure above the solution is reduced, and CO2 begins to escape from the solution. • Effervescence: the rapid escape of a gas from a liquid
Temperature and Solubility of Gas • Increasing the temperature… Increases the average kinetic energy and allows more solute to escape the attraction of the solvent and escape to the gas phase • At higher temperatures, equilibrium is reached with fewer gas molecules in solution
Temperature and Solubility of Liquids and Solids • Increasing the temperature… Increases in temperature usually increases the solubility of solids in liquids • The solubility depends on the solid and properties of the solid. • A few solid solutes are actually less soluble at higher temperatures.