Pearson Prentice Hall Physical Science: Concepts in Action Chapter 8 Solutions, Acids & Bases

8.1 Formation of Solutions Objectives: 1. Describe how a substance can dissolve in water by dissociation, dispersion or ionization 2. Describe how physical properties of a solution can differ from those of its solute and solvent 3. Identify energy changes that occur during formation of a solution 4. Describe factors affecting the rate at which a solute dissolves in a solvent

Dissolving: Dissociation, Dispersion or Ionization Substances can dissolve in water by three ways: 1. dissociation 2. dispersion 3. ionization Definition: dissociation is the process by which an ionic compound separates into ions Ex: NaCl

Definition: dispersion is the process by which a compound breaks into small pieces that spread throughout the water Ex: sugar dissolves in water Definition: ionization is the process by which neutral molecules gain or lose electrons (forming ions) Ex: hydrogen chloride gas & water react to form hydronium ion (H3O+) and chlorine ion (Cl-)

Physical Properties: Solute & Solvent Definition: a solute is a substance whose particles are dissolved in a solution (often a solid) Definition: a solvent is the substance in which the solute dissolves (often a liquid) Solutes and solvents can take the form of solids, liquids or gases The solution takes the state of the solvent

Three physical properties of a solution that can differ from those of its solute and solvent are conductivity, freezing point & boiling point Definition: conductivity is the ability of a solution to conduct electricity Ex: NaCl is a poor conductor until it is placed in water & dissociates

Definition: the freezing point is the temperature at which a liquid becomes a solid Freezing point is changed with the addition of ionic compounds like MgCl2 or other ionic compounds The freezing point is lowered when ionic compounds are added

Definition: the boiling point is the temperature a liquid substance becomes a gas Coolants used in radiators (ethylene glycol, a molecular substance) raise the boiling point of water & keeps the engine from overheating Formation of new solutions by the addition of ionic or molecular compounds requires an energy change

Energy Changes & Solution Formation During formation of a solution, energy is either released or absorbed The process is endothermic or exothermic Forming attractions releases energy (exothermic) Breaking attractions requires or absorbs energy (endothermic)

Factors that Affect Dissolving Rate Factors that affect the rate of dissolving include surface area, stirring and temperature Dissolving takes place at the surface The greater the surface area, the faster the dissolving Stirring or shaking makes a substance dissolve faster by increasing the surface area exposed to the solvent

8.2 Solubility and Concentration Objectives: 1. Define solubility and describe factors affecting solubility 2. Classify solutions as unsaturated, saturated or supersaturated

Solubility & Factors Affecting Solubility Definition: solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature Solutions are classified as saturated, unsaturated or supersaturated The classification depends on the amount of solute in solution

3 types of solutions Definition: a saturated solution is one that contains as much solute as the solvent can hold at a given temperature Definition: an unsaturated solution has less than the amount of solute that can be dissolved Definition: a supersaturated solution contains more solute than the solution can normally hold at a given temperature

8.3 Properties of Acids and Bases Objectives: 1. Define acid and describe the general properties of an acid 2. Define base and describe some of the general properties of a base

Acids Definition: an acid is a compound that produces hydronium ions (H3O+) when dissolved in water Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators Definition: an indicator is any substance that changes color in the presence of an acid or a base

Bases Definition: a base is a compound that produces hydroxide ions (OH-) when dissolved in water Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators

Strength of Acids and Bases Objective: 1. define pH and relate pH to hydronium ion concentration ----------------------------------------------- Definition: pH of a solution is a measure of its hydronium ion concentration

A pH of 7 indicates a neutral solution Water is the standard for pH 7 The pH scale runs from 0 – 14 The lower the pH, the higher the higher the hydronium ion concentration

The higher the hydronium ion concentration, the more acidic the substance is A high pH value means a low H3O+ concentration The lower H3O+ concentration, the more basic or alkaline the solution is