Pearson Prentice Hall Physical Science: Concepts in Action

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

2. 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

3. 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

4. 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-)

5. 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

6. 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

7. 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

8. 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

9. 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)

10. 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

11. 8.2 Solubility and Concentration • Objectives: • 1. Define solubility and describe factors affecting solubility • 2. Classify solutions as unsaturated, saturated or supersaturated

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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