1. Chapter 3: “Acids, Bases, and Solutions” Section 1: “Working With Solutions”

2. Lesson Objectives  After completing the lesson, students will be able to: Define and compare solutions and suspensions; Explain what happens to particles of a solute when a solution forms; Identify the factors that affect solubility of a substance; Describe how solutes affect the freezing and boiling points of solvents.

3. Solutions and Suspensions  Suspension —is a mixture in which particles can be seen and easily separated by settling or filtration. Not easily mixed –Example: Mixing pepper and water  Solution —a well-mixed mixture A solution has the same properties throughout –Example: Saltwater

4. Solvents and Solutes  All solutions have at least two parts: Solvents and the solute  Solvents —the part of a solution present in the largest amount.  Solutes —a substance that is present in a solution in a smaller amount and dissolved by the solvent. In saltwater, the solvent is the water and the solute is the salt. In many common solutions, the solvent is water. Water dissolves so many substances that it is often called the “universal solvent.”

5. Solutions Without Water  Many solutions are made with solvents other than water.  For example, gasoline is a solution of several different liquid fuels. You don’t even need a liquid solvent to make solutions.  A solution may be made of any combination of gases, liquids, or solids.

6. Particles in a Solution  Whenever a solution forms, particles of the solute leave each other and become surrounded by particles of the solvent.

7. Particles in a Solution  Ionic Solids in Water: (page 82) The positive and negative ions are attracted to polar water molecules. Water molecules surround each ion as it leaves the surface of the crystal. As each layer of the solid is exposed, more ions can dissolve.  Molecular Solids in Water (page 83) A molecular solid, such as sugar, breaks up into individual neutral molecules. The polar molecules attract the slightly polar sugar molecules. This causes the sugar molecules to move away from each other. Covalent bonds within the molecules are undisturbed. Like ions, the sugar molecules become surrounded by water.

8. Solutions and Conductivity  Read this section on page 83.

9. Concentration  Concentration—The amount of one material in a certain volume of another material.  Dilute Solution—A mixture that has little solute dissolved in it.  Concentrated Solution—A mixture that has a lot of solute dissolved in it.

10. Solubility  Solubility —is a measure of how well a solute can dissolve in a solvent at a given temperature.  Saturated Solution —A mixture that has so much solute in it that no more will dissolve.  Unsaturated Solution —A mixture in which more solute can be dissolved The solubility of a substance is usually described for a specific solvent (such as water) and under certain conditions (such as temperature).

11. Changing Solubility  Among the factors that affect the solubility of a substance are temperature and type of solvent.

12. Changing Solubility  Temperature: Many solids dissolve better when the temperature of a solvent increases. Gases become less soluble when the temperature goes up.  Solvents: Polar compounds and nonpolar compounds do not mix very well. For liquids solutions, the solvent affects how well a solute dissolves. Ionic and polar compounds dissolve in polar solvents. Nonpolar compounds do not dissolve in polar solvents

13. Effects of Solutes on Solutions  Lower Freezing Points: Solutes lower the freezing point of a solvent. When liquid water freezes, the molecules stop moving about. They form crystals of solid ice. The solute particles (salt added to water) make it harder for the water molecules to form crystals. The temperature must drop lower than 0 degree C for a solid to form.  Higher Boiling Points: Solutes raise the boiling point of a solvent. As the temperature of a liquid rises, the molecules gain energy and escape into the air. The presence of the solute makes it harder for the water molecules to escape, so more energy is needed. The temperature must go higher than 100 degrees C for the water to boil.

14. Chapter 3: “Acids, Bases, and Solutions” Section 2 “Describing Acids and Bases”

15. Objectives  After completing the lesson, students will be able to: Identify and describe the properties of acids and give examples; Identify and describe the properties of bases and give examples.

16. Properties of Acids  Acids —a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus paper red.  Sour Taste: Although sour taste is a property of many acids, it is not one you would use to identify a compound. Though acids in sour foods may be safe to eat, many other acids are not.

17. Properties of Acids  Reactions with Metals: Acids react with certain metals to produce hydrogen gas. Not all metals react this way. Acids are described as corrosive, which means they “eat away” at other materials.

18. Some Important Acids  Hydrochloric Acid = HCl  Nitric Acid=HNO 3  Sulfuric Acid=H 2 SO 4  Carbonic Acid=H 2 CO 3  Acetic Acid=HC 2 H 3 O 2  Phosphoric Acid =H 3 PO 4

19. Properties of Acids  Reactions With Carbonates: When acids react with carbonate compounds, a gas forms. Geologists use the reaction of acids with carbonates to identify certain things.  Reaction with Indicators: Litmus paper is an example of an indicator. Indicator —a compound that changes color when in contact with an acid or a base. Acids always turn litmus paper red.

20. Properties of Bases  Bases —a substance that tastes bitter, feels slippery, and turns red litmus paper blue.  Often described as the “opposites” of acids.

21. Properties of Bases  Bitter Taste: Bases taste bitter. Example of bases include soaps, shampoo, and detergents.  Slippery Feel: Strong bases can irritate or burn your skin.

22. Properties of Bases  Reactions with Indicators: Bases turn litmus paper blue.  Reaction of Bases: Bases do not react with metals or carbonates. Another important property of bases is how they react with acids (This is covered in Section 3).

23. Chapter 3: “Acids, Bases, and Solutions” Section 3 “Acids and Bases in Solution”

24. Objectives  After completing the lesson, students will be able to: Describe the ions formed when acids and bases are dissolved in water; Describe the pH scale and tell how it is used; Explain what happens in a neutralization reaction

25. Acids in Solution  The acids we are learning about are made of one or more hydrogen ions and a negative ion.  Hydrogen Ion (H+)—an atom of hydrogen that has lost its election.  Hydrogen ions are the key to the reactions of acids.  An acid is any substance that produces hydrogen ions (H+) in water.  Hydrogen ions also react with blue litmus paper, turning it red. That’s why ever acid gives the same litmus test result.

26. Bases in Solution  Many bases are made of metals combined with hydroxide ions.  Hydroxide Ion (OH-)—is a negative ion made of oxygen and hydrogen.  When bases dissolve in water, positive metal ions and hydroxide ions separate.  Not every base contains hydroxide ions.  A base is any substance that produces hydroxide ions (OH-) in water.

27. Strength of Acids and Bases  Strength refers to how well an acid or base produces ions in water.  In strong acids, most of the molecules react to form hydrogen ions in solution. In weak acids, fewer molecules do.  A strong base produces more hydroxide ions (OH-) than does an equal concentration of a weak base.  Strength determines how safe acids and bases are to use.

28. Measuring pH  pH Scale —a range of values from 0 to 14, which expresses the concentration of hydrogen ions in a solution.  The most acidic substances are at the low end of the scale. The most basic substances are at the high end of the scale.  A low pH tells you that the concentration of hydrogen ions is high. By comparison, a high pH tells you that the concentration of hydrogen ions is low.

29. Measuring pH  You can find the pH of a solution by using indicators (litmus paper).  A pH lower than 7 (neutral) is acidic.  A pH higher than 7 is basic.

30. Examples of Acids and Bases  Acids: pH level below 7 Hydrochloric Acid Lemon Vinegar Apple Tomato Banana Milk  Bases: pH level above 7 Blood Baking Soda Soap Ammonia Drain Cleaner

31. Acid Rain  Normal rainfall is acidic, with a pH of approximately 5.5.  The acidity comes from carbon dioxide in the air.  Acid Rain —rainwater that is more acidic than the norm, ranging approximately 3.5 to 3.0 on the pH scale.

32. Acid-Base Reactions  Neutralization —a reaction between an acid and a base.  As a result of neutralization, an acid-base mixture is not as acidic or basic as the individual starting solutions were.  Sometimes an acid-base reaction results in a neutral solution, but not always.  The final pH depends on which acid and base react, how much of each is used, and what their concentrations are.

33. Products of Acid-Base Reactions  Salt —any ionic compound made from the neutralization of an acid with a base. A salt is made form the positive ion of a base and the negative ion of an acid.  A neutralization reaction produces water and a salt.

34. Example of Salts (page 101)  Sodium Chloride —NaCl—Food flavoring; preservative  Potassium iodide —Kl—Additive in “iodized” salt that prevents iodine deficiency  Calcium chloride —CaCl 2 —De-icer for roads and walkways  Potassium chloride —KCl—Salt substitute in foods  Calcium carbonate —CaCO 3 —Found in limestone and seashells  Ammonium nitrate —NH 4 NO 3 —Fertilizer; active ingredient in some cold packs.

35. Chapter 3: “Acids, Bases, and Solutions” Section 4 “Digestion and pH”

36. Objectives  After completing the lesson, students will be able to: Distinguish between mechanical and chemical digestion, and tell the importance of each; Explain how pH affects digestion.

37. What is Digestion?  Foods are made mostly of water and three groups of compounds: Carbohydrates, Proteins, and Fats.  Foods must be broken down into simpler substances that your body can use for raw materials and energy.  Digestion —a process of breaking down the complex molecules of foods into smaller molecules.

38. 2 Types of Digestion  Mechanical digestion — tears, grinds, and mashes large food particles into smaller ones.  The size of the food is reduced, but the foods aren’t changed into other compounds.  Chemical digestion — breaks large molecules into smaller molecules.  Chemical digestion takes place with the help of enzymes (speed up reactions in living things).  For some digestive enzymes, the pH must be low. For others, the pH must be high or neutral.

39. pH in the Digestive System  Your Mouth — your teeth chew and mash up food, the food is mixed with saliva, which contains amylase (am uh lays) that helps break down the carbohydrate starch into smaller sugar molecules  Your Stomach —This muscular organ starts digestion of foods that contain protein. Cells in the lining of your stomach release enzymes and hydrochloric acid.  The main enzyme that works in your stomach is pepsin, which helps break down proteins into small molecules called amino acids.

40. pH in the Digestive System  Your Small Intestines — Other digestive fluids, which contain the bicarbonate ion HCO 3 -, surround the food.  Other enzymes complete the breakdown of carbohydrates, fats, and proteins.  Most chemical digestion ends in the small intestine.  pH changes during digestion:  Mouth —pH level 7  Stomach —pH level 2  Small Intestine —pH level 8