Chapter 12

1. Chapter 12 12.1 Types of Mixtures Solutions

2. Solutions are homogeneous mixtures! Classification of Matter

3. Salt in salt water Solute A solute is the dissolved substance in a solution. Carbon dioxide in soda drinks Sugar in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda

4. Types of Solutions • Gaseous mixtures Air is a solution • Solid solutions Metal alloys • Liquid solutions Liquid dissolved in a liquid (alcohol in water) Solid dissolved in a liquid (salt water)

5. Concentrated vs. Dilute

6. Suspensions and Colloids Suspensions and colloids are NOT solutions. Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred. Particles can be filtered out. Example: Oil & Water Colloids: The particles intermediate in size between those of a suspension and those of a solution. Particles cannot be easily filtered out. Example: Milk

8. Gelatin is protein in water. Quicksand is sand in water Mayonnaise is oil in water Milk of Magnesia is a sol with solid magnesium hydroxide in water Smoke is a solid in a gas. Fog is a liquid in a gas.

9. The Tyndall Effect Colloids scatter light, making a beam visible. Solutions do not scatter light. Which glass containsa colloid? colloid solution

10. Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

11. Definition of Electrolytes and Nonelectrolytes An electrolyte is: • A substance whose aqueous solution conducts • an electric current. A nonelectrolyte is: • A substance whose aqueous solution does not • conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes…

12. Electrolytes? • Pure water • Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure sodium chloride

13. Answers to Electrolytes Electrolytes: Nonelectrolytes: • Tap water (weak) • NaCl solution • HCl solution • Lactate solution (weak) • Pure water • Sugar solution • Ethanol solution • Pure NaCl But why do some compounds conduct electricity in solution while others do not…?

14. Chapter 12 12.2 The Solution Process Solutions

15. The Hydration Process Dissolution of sodium Chloride

16. Saturation of Solutions • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. • A solution that contains less solute than a saturated solution under existing conditions is unsaturated. • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

18. Factors Affecting the Rate of Dissolution • Increasing the Surface Area of the Solute Finely divided substances dissolve more rapidly • Agitating a Solution Stirring or shaking brings solvent into contact with more solute particles Added energy temporarily increases solubility • Heating Heating always increasing the rate of dissolution of solids in liquids

19. “Like dissolves like” • Polar substances dissolve in polar solvents • Nonpolar substances dissolve in nonpolar solvents • Examples: • Polar and ionic compounds are not soluble in nonpolar solvents • Fats, oils and many petroleum products are soluble in nonpolar solvents • Nonpolar solvents include CCl4 and toluene (methyl benzene), C6H5CH3

20. Liquid Solutes and Solvents Immiscible - Liquid solutes and solvents that are not soluble in each other Ex: Oil and water Miscible - Liquids that dissolve freely in one another in any proportion Ex: Benzene and carbon tetrachloride (both nonpolar) Ex: Water and ethanol (both polar) • Hydrates Ionic substances that incorporate water molecules into their structure during the recrystallization process Ex: CuSO4•5H2O

22. Saturation and Equilibrium The physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates

23. Effects of Pressure on Solubility • Pressure has no real effect on the solubilities of liquids and solids in liquid solvents • Increasing pressure increases the solubility of gases in liquids • Henry's Law • The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid • Effervescence • The rapid escape of a gas from a liquid in which it is dissolved

24. Effects of Temperature on Solubility • Solubility of solids increases with temperature • Solubility of gases decreases with temperature

25. Solubility Trends • The solubility of MOST solids increases with temperature. • The rate at which solids dissolve increases with increasing surface area of the solid. • The solubility of gases decreases with increases in temperature. • The solubility of gases increases with the pressure above the solution.

26. Therefore… Solids tend to dissolve best when: • Heated • Stirred • Ground into small particles Liquids & Gases tend to dissolve best when: • The solution is cold • Pressure is high

27. Heat of Solution The Heat of Solution is the amount of heat energy absorbed (endothermic, positive) or released (exothermic, negative) when a specific amount of solute dissolves in a solvent.

28. Chapter 12 12.3 Concentration of Solution Solutions

29. Molarity The concentration of a solution measured in moles of solute per liter of solution. mol= M L Pronounced “molar”

32. Molality The concentration of a solution in moles of solute per kilogram of solvent. mol= m kg Since the most common solvent, water, has a density of 1 kg/L, one kilogram of water is the same as one liter of water!