Formation of Solutions: Dissociation, Dispersion, and Ionization

1. Chapter 8 Solutions, Acids, and Bases

2. 8-1 Formation of Solutions • Substance can dissolve in water three ways-by dissociation, dispersion, and ionization • A solute is a substance whose particles are dissolved in a solution. • The substance in which the solute dissolves is called the solvent. • Ex: Seawater • Solute = is the salt • Solvent = is the water

3. Solutes/Solvents • Solutes and solvents can take the form of a solid, liquid or gas. • The solution takes the state of the solvent.

4. Dissociation of Ionic Compounds • Dissociation is the process in which an ionic compound separates into ions as it dissolves. • For a solute to dissolve in water, the solute and solvent particles must attract one another. • Before a solution can form, the attractions that hold the solute together and the solvent together must be overcome

5. Dispersion of Molecular Compounds • Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water. • Ex: piece of candy disperses throughout your mouth • Water in saliva dissolves the sugar and flavoring in the candy.

6. Process of Dispersion • When enough water molecules surround a sugar molecule, the attractions between them are great enough to overcome the attractions holding the sugar molecule to the surface of the crystal. • The sugar molecule breaks free, and is pulled into solution by the water molecules, then another layer if sugar molecules is exposed to the water

7. Ionization of Molecular Compounds • The process in which neutral molecules gain or lose electrons is known as ionization. • Dissolving by ionization is a chemical change. • The solution that results contains new substances. • When a solute dissolves by ionization, the ions in solution are formed by the reaction of solute and solvent particles.

8. Example of Ionization • When water and hydrogen chloride form a solution, two molecular compounds react to form two ions. • Ions formed are H3O+ and Cl- • Drawing

9. Answer the following Questions • What are three ways that substances can dissolve in water? • How does sugar dissolve in water?

10. 8-1 ContinuedProperties of Liquid solutions • Three physical properties of a solution that can differ from those of its solute and solvent are: • Conductivity • Freezing Point • Boiling Point

11. Conductivity • Solid sodium chloride is a poor conductor of electricity • Sodium chloride dissociates in water and the ions formed can move freely enabling them to conduct electricity

12. Freezing Point • The freezing point of water at sea level is 0 degrees Celsius • Example : icy roads are salted with magnesium chloride, the resulting solution can have a freezing point as low as -15 degrees Celsius

13. Boiling Point • A solute can raise the boiling point of the solvent • Example: the coolant used in most car radiators is a solution containing water and ethylene, which raises the boiling point. This helps the engine from overheating.

14. Heat of Solution • During the formation of a solution, energy is either released or absorbed. • In order for a solution to form, both the attractions among the solute particles and the attractions among the solvent particles must be broken. • Breaking attractions requires energy.

15. Heat of Solution Continued • As the solute dissolves, new attractions form between solute and solvent particles. • The formation of attractions releases energy. • The difference between these energies is known as heat of solution

16. Factors Affecting Rates of Dissolving • Factors that affect the rate of dissolving include: • Surface area • Stirring • Temperature

17. Surface Area • The greater the surface area of a solid solute, the more frequent the collisions are between solute and solvent particles. • More collisions result in faster rate of dissolving

18. Stirring • Stirring moves dissolved particles away from the surface of the solid, and allows for more collisions between the solute and solvent particles

19. Temperature • Increasing the temperature of the solvent speeds up the dissolving rate. • This causes its particles to move faster. • As a result, both the number of collisions and the energy of these collisions with solute particles increase. • The solute goes into the solution more quickly.

20. Beaker Breaker • List the three factors that affect the rate of dissolving. • Sugar dissolves in water by___________, or breaking into small pieces that spread throughout the water

21. Section 8-1 Review • Using your book complete the following questions: • Page 257 • Numbers 1,2,3,4,5

22. Section 8-2 • The maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature is called solubility • Ex: sugar in lemonade • Knowing the solubility of a substance can help you classify solutions based on how much solute they contain.

23. Solubility • Solutions are described as: • saturated, • unsaturated, • Supersaturated • depending on the amount of solute in solution.

24. Saturated Solutions • Table sugar is very soluble in water • A saturated solution is one that contains as much solute as the solvent can hold at a given temperature. • When a solution is saturated, the solvent is “filled” with solute. • If you add more solute, it will not dissolve.

25. Unsaturated Solutions • A solution that has less than the maximum amount of solute that can be dissolved is called an unsaturated solution. • Example: many beverages you drink are unsaturated solutions of sugar in water. • As long as the amount of solute is less than the solubility at that temperature, the solution is unsaturated

26. Supersaturated Solutions • A supersaturated solution is one that contains more solute than it can normally hold at a given temperature. • Supersaturated solutions are very unstable. • Ex: carrying a stack of books

27. Review Questions • What terms are used to describe solutions with different amounts of solute. • How does a supersaturated solution differ from a saturated solution?

28. How Cold Packs Work • Read page 233 in your book • Discussion

29. 8-2 Continued • Factors Affecting Solubility • Three factors that affect the solubility of a solute are: • The polarity of solvent • Temperature • Pressure

30. Polar and Nonpolar Solvents • Oil does not dissolve in water because oil molecules are nonpolar and water molecules are polar • A common guideline for predicting solubility is “like dissolves like” • Solution formation is more likely to happen when the solute and solvent are either both polar or both nonpolar

31. Temperature • In general, the solubility of solids increases as the solvent temperature increases. • Example: sugar added to cold tea verses hot tea • Gases usually become less soluble as the temperature of the solvent increases

32. Pressure • Increasing the pressure on a gas increases its solubility in a liquid • Carbonated beverages, uses pressure to force CO2 to dissolve in the liquid • The pressure of CO2 in a sealed 12-ounce can of soda at room temp can be two to three times atmospheric pressure.

33. Concentrations of Solutions • The concentration of a solution is the amount of solute dissolved in a specified amount of solution • Concentrations can be expressed as percent by: volume, percent by mass, and molarity.

34. Percent by Volume • Percent by Volume = Volume of solute x 100% • Volume of solvent Example the volume of the solute is 10 L and the volume of the solvent is 30 L. What is the percent by volume?

35. Percent by Mass • Concentration expressed as a percent by mass is more useful when the solute is a solid. • Percent by mass = Mass of solute x 100% • Mass of solution • Example: Suppose you have 100grams of a solution of sugar in water. After allowing the water to evaporate, 15 grams of sugar remains. What is the percent by mass?

36. Molarity • Molarity is the number of moles of a solute dissolved per liter of a solution. • Molarity = moles of solute x 100% • Liters of solution

37. Example of Molarity • To make 1-molar (1M) of solution of sodium chloride in water • First calculate the molar mass of the solute (NaCl) = _________ • If 58.5 grams of sodium chloride is mixed with enough water to make one liter of solution, the resulting solution is 1-molar.

38. Complete the following Questions 1.)What are three ways that substances can dissolve in water? 2. What physical properties of a solution differ from those of its solutes and solvents? 3. How does the formation of a solution involve energy? 4. What factors affect dissolving rates? 5. Identify the processes by which sugar crystals and hydrogen chloride gas dissolve in water.

39. 8-3 Properties of Acids and Bases • There are several differences among acidic solutions, basic solutions, and solutions that have properties neither an acid or nor a base

40. Identifying Acids • An acid is a compound that produces hydronium ions (H3O+) when dissolved in water. • Ex: HCl + H2O H3O+ + Cl- • Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators

41. Sour Taste • Foods that taste sour often contain acids • Ex: lemons, grapefruits, limes, and oranges all contain citric acid. • Vinegar contains acetic acid. • Dairy products that have spoiled contain butyric acid

42. Reactivity with Metals • When you use aluminum foil to cover a bowl of leftover spaghetti sauce or other foods containing tomatoes the foil often turns dark. • Tomatoes contain citric acid, which reacts with metals such as aluminum

43. Reactivity with Metals • The reaction between an acid and a metal is an example of single replacement reaction. • Ex: Zinc is added to hydrochloric acid. Zn +2HCl  H2 + ZnCl2 • As zinc replaces hydrogen in hydrochloric acid, hydrogen gas and zinc(II) chloride is produced

44. Color Changes in Indicators • An indicator is any substance that changes color in the presence of an acid or base. • One of the most common indicators used is litmus, a kind of dye derived from plants called lichens. • Litmus paper is made by coating strips of paper with litmus. • Blue litmus paper turns red in the presence of an acid.

45. Testing Acids on litmus paper • Observations • Vinegar – • HCl – • Sulfuric Acid – • Acetic Acid -

46. Identifying Bases • Sodium hydroxide, NaOH is an example of a base. • A base is a compound that produces hydroxide (OH-) when dissolved in water. • NaOH  Na++ OH-

47. Bases • Bases have certain physical and chemical properties that you can use to identify them. • Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators

48. Properties of Bases • Bitter Taste • Slippery Feel • Color Changes in indicators

49. Bitter Taste • Baking chocolate (without the sugar) • Cough syrups and other liquid medicines

50. Slippery Feel • Bases feel slippery. • Wet soap and many cleaning products that contain bases are slippery to the touch. • When wet, some rocks feel slippery because water dissolves compounds trapped in the rocks, producing a basic solution.