Letter to the Student... 5 Test-Taking Checklist... 6 Next Generation Sunshine State Standards Correlation Chart... 7

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2 Table of Contents Letter to the Student Test-Taking Checklist Next Generation Sunshine State Standards Correlation Chart... 7 Florida Benchmarks Chapter 1 Understanding Science Lesson 1 The Characteristics of Scientific Knowledge SC.8.N.2.1, SC.8.N.2.2 Lesson 2 Understanding Scientific Investigation.. 16 SC.8.N.1.1, SC.8.N.1.5, SC.8.N.1.6 Lesson 3 Repeated Trials and Replication SC.8.N.1.1, SC.8.N.1.2, SC.8.N.1.4 Lesson 4 Interpreting and Displaying Results SC.8.N.1.1, SC.8.N.1.6, SC.8.N.3.1 Lesson 5 Drawing Conclusions SC.8.N.1.1, SC.8.N.1.3 Lesson 6 Modifying and Revising Theories SC.8.N.1.6, SC.8.N.3.2 Lesson 7 Science and Society SC.8.N.4.1, SC.8.N.4.2 Chapter 1 Review Chapter 2 Our Solar System Lesson 8 Historical Knowledge of Our Solar System SC.8.E.5.8 Lesson 9 Gravity SC.8.E.5.4 Lesson 10 Properties of the Sun SC.8.E.5.6 Lesson 11 The Objects of Our Solar System SC.8.E.5.7 Lesson 12 Earth in the Solar System SC.8.E.5.9 Lesson 13 The Effects of Earth s Moon on Earth.. 73 SC.8.E.5.9 Lesson 14 Relative Positions of the Sun, Earth, and Moon SC.8.E.5.9 Chapter 2 Review Duplicating any part of this book is prohibited by law. 3

3 Chapter 3 Outer Space Lesson 15 Understanding Distances in Space SC.8.E.5.1, SC.8.E.5.2, SC.8.E.5.3 Lesson 16 Properties of Stars SC.8.E.5.5 Lesson 17 Applications of the Electromagnetic Spectrum Lesson 18 Technology and Its Contributions to Astronomy Lesson 19 Space Exploration and Its Effects on Florida Chapter 3 Review SC.8.E.5.11 SC.8.E.5.10, SC.8.E.5.11 SC.8.E.5.12 Chapter 4 Properties of Matter Lesson 20 Physical Properties of Matter SC.8.P.8.1, SC.8.P.8.2, SC.8.P.8.3, SC.8.P.8.4 Lesson 21 Atomic Theory SC.8.P.8.7 Lesson 22 The Periodic Table of Elements SC.8.P.8.6 Lesson 23 Common Compounds SC.8.P.8.5, SC.8.P.8.8 Lesson 24 Identifying Mixtures SC.8.P.8.4, SC.8.P.8.9 Chapter 4 Review Chapter 5 Changes in Matter Lesson 25 Comparing Physical and Chemical Changes SC.8.P.8.5, SC.8.P.8.9, SC.8.P.9.2, SC.8.P.9.3 Lesson 26 Temperature and Changes in Matter SC.8.P.8.1, SC.8.P.9.2 Lesson 27 The Law of Conservation of Mass SC.8.P.9.1 Lesson 28 Acids, Bases, and Salts SC.8.P.8.8 Lesson 29 Chemical Changes and Balance in Living Systems Chapter 5 Review Investigation 1: Separating Mixtures Investigation 2: Exploring Acids and Bases Glossary SC.8.L.18.1, SC.8.L.18.2, SC.8.L.18.3, SC.8.L Duplicating any part of this book is prohibited by law.

4 28 X Acids, Bases, and Salts SC.8.P.8.8 Getting the Idea Key Words ion acid base ph scale neutral neutralization reaction salt What do lemons and batteries have in common? What do baking soda and soap have in common? The answer is that lemons and batteries are acidic, while baking soda and soap have properties of bases. In this lesson, you will learn about acids and bases and explore what happens when they mix together. Acids and Bases In everyday life, you might think of strong liquids that can eat away or corrode objects as acids. However, this is not always the case. There are scientific reasons why substances are either acids or bases. These reasons depend on the atoms that make up the substance and what the substances release when they dissolve in water. Recall that a normal uncharged atom has the same number of electrons as its number of protons. However, some atoms have more or less electrons. An ion forms when an atom gains or loses electrons and becomes electrically charged. Acids An acid is any substance that releases hydrogen ions (H+) in solution. Acids can easily be recognized by their chemical formulas. Acids generally have formulas whose first element is H. For example, HCl is hydrochloric acid, the acid present in the human stomach. H 2 SO 4 is sulfuric acid, an acid present in batteries. 158 Duplicating any part of this book is prohibited by law.

5 Lesson 28: Acids, Bases, and Salts Did You Know Indicators are used to identify acidic and basic substances. An indicator is a substance that changes color in the presence of an acid or a base. Some indicators are red and blue litmus paper, red cabbage juice, bromthymol blue, and ph paper. Acids have properties that make them different from other substances. Have you ever tasted a slice of lemon or a lime? A property of acids is a sour taste. Lemons, limes, and other citrus fruits contain citric acid. Vinegar is an acid. Foods such as pickles are soaked in vinegar, which is why they also taste sour. PICKLES JUICE Carbonated SODA Vitamin C VINEGAR Some acids can be harmful. Strong acids are corrosive, which means they can eat through plastics, clothing, and even skin. Acids can also eat through some metals. For this reason, you should never touch or taste acids if you are unfamiliar with them. Even if you think it is safe, never taste a sample unless you are told to do so by a trusted adult such as your teacher. Bases A base is any substance that releases hydroxide ions (OH ) in solution. Many bases have chemical formulas that end in OH. For example, NaOH is sodium hydroxide, a base used in drain cleaner. Calcium hydroxide, Ca(OH) 2, is a base used to make fertilizers, plaster, and cement. Bases have many properties that make them different from other substances. Bases taste bitter. They also feel slippery. A good example of a base is soap. If you have ever accidentally tasted soap, you know that it has a very bitter taste. Soap is also very slippery. Another example of a base is baking soda. SOAP FERTILIZER DISH LIQUID BAKING SODA DRAIN CLEANER Duplicating any part of this book is prohibited by law. 159

6 Although bases are in some ways the opposite of acids, this does not mean that they are never dangerous. Like acids, some bases can be harmful. Strong bases are as corrosive as strong acids and can eat through many materials. It is important that you never touch or taste a base if you are unfamiliar with it. The table below summarizes the characteristics of acids and bases. Properties of Acids Taste sour Release H+ ions React with metals to produce hydrogen gas bubbles Have a ph <7 Turn blue litmus paper red Properties of Both Acids and Bases Can cause burns if concentrated; handle with care Can conduct electric current when mixed with water React chemically when mixed together Properties of Bases Taste bitter Release OH ions Feel slippery to the touch Have a ph >7 Turn red litmus paper blue ph Scale The strength of an acid or base is identified by a number from 0 through 14. This number is called its ph. The ph scale runs from 0 to 14, with low numbers being stronger acids, high numbers being strong bases, and the number 7 being neutral, neither an acid or a base. Hydrochloric acid in water forms a very strong acid with a ph of 1. Sodium hydroxide in water forms a strong base that has a ph of about 13. This is the active ingredient in many household drain cleaners. Pure water is a neutral substance with a ph of 7. Neutral substances do not share properties with either acids or bases. HCl Lemon juice Pure water Soap NaOH Acid Neutral Base 160 Duplicating any part of this book is prohibited by law.

7 Lesson 28: Acids, Bases, and Salts When Acids and Bases Mix Most liquids you come into contact with are either acids or bases. A neutralization reaction is a chemical reaction in which an acid and a base mix, react chemically, and form both water and a salt. A salt is a solid compound that forms when an ion of a metal replaces the hydrogen ion of an acid. During a neutralization reaction, the H+ ions bond with the OH ions. Together the ions become water (H 2 O) with a ph of 7. The remaining atoms join together to form a salt. A few typical neutralization reactions are as follows: HCl (acid) + NaOH (base) NaCl (a salt) + H 2 O (water) H 2 SO 4 (acid) + Ca(OH) 2 (base) CaSO 4 (a salt) + 2(H 2 O) (water) KNO 3 (acid) + KOH (base) KNO 3 (a salt) + H 2 O (water) Each example above shows that mixing an acid and a base together produces a different type of salt and water. DISCUSSION QUESTION Many environmentally-friendly Web sites suggest making your own drain cleaner of white vinegar, lemon juice, baking soda, and very hot water. What do you think might make a homemade drain cleaner like this effective? LESSON REVIEW 1. Which of the following substances is a base? A. vinegar B. lemon juice C. water D. liquid soap Duplicating any part of this book is prohibited by law. 161

8 2. An unknown substance is dissolved in water. The solution is corrosive, conducts electricity, and has a higher concentration of H+ ions than OH ions. What kind of solution does this unknown substance form? A. an acidic solution B. a basic solution C. a neutral solution D. There is no way to tell whether it is an acid or a base. 3. Citrus fruits generally have a ph less than 7. Based on this information, you can say that these citrus fruits are A. neutral. B. acids. C. bases. D. electrically charged. 162 Duplicating any part of this book is prohibited by law.