1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids and Their Properties An acid is any compound that increases the number of hydronium ions, H 3 O +, when dissolved in water. Hydronium ions form when a hydrogen ion, H +, separates from the acid and bonds with a water molecule, H 2 O, to form a hydronium ion, H 3 O +. Chapter 15 Section 2 Acids and Bases

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids and Their Properties, continued Acids Have a Sour Flavor The sour taste of lemons, limes, and other citrus fruits is a result of citric acid. Taste, touch, or smell should NEVER be used to identify an unknown chemical. Many acids are corrosive, which means that they destroy body tissue, clothing, and many other things. Most acids are also poisonous. Chapter 15 Section 2 Acids and Bases

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids and Their Properties, continued Acids Change Colors in Indicators A substance that changes color in the presence of an acid or base is an indicator. Chapter 15 Section 2 Acids and Bases This flask contains water and an indicator called bromthymol blue.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids and Their Properties, continued Acids Conduct Electric Current When acids are dissolved in water, they break apart and form ions in the solution. The ions make it possible for the solution to conduct an electric current. A car battery is one example of how an acid can be used to produce an electric current. The sulfuric acid in the battery conducts electricity to help start the car’s engine. Chapter 15 Section 2 Acids and Bases

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bases and Their Properties A base is any compound that increases the number of hydroxide ions, OH -, when dissolved in water. For example, sodium hydroxide breaks apart to form sodium ions and hydroxide ions, as shown in this formula NaOH  Na + = OH - Chapter 15 Section 2 Acids and Bases

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bases and Their Properties, continued Bases Have a Bitter Flavor and a Slippery Feel If you have ever tasted soap, you know the bitter taste of a base. Soap will also have the slippery feel of a base. Taste, touch, or smell should NEVER be used to identify an unknown chemical. Like acids, many bases are corrosive. Chapter 15 Section 2 Acids and Bases

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bases and Their Properties, continued Bases Conduct Electric Current Solutions of bases conduct electricity because bases increase the number of hydroxide ions, OH -, in a solution. A hydroxide ion is actually a hydrogen atom and an oxygen atom bonded together. The extra electron gives the hydroxide ion a negative charge. Chapter 15 Section 2 Acids and Bases

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Strengths of Acids and Bases Acids and bases can be strong or weak. Strength of an acid or a base is not the same as the concentration of an acid or a base. The concentration of an acid or a base is the amount of acid or base dissolved in water. The strength of an acid or a base depends on the number of molecules that break apart when the acid or base is dissolved in water. Chapter 15 Section 3 Solutions of Acids and Bases

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Strengths of Acids and Bases, continued Strong Versus Weak Acids As an acid dissolves in water, the acid’s molecules break apart and produce hydrogen ions, H +. If all the molecules break apart, the acid is called a strong acid. Strong acids include sulfuric acid, nitric acid, and hydrochloric acid. If only a few molecules break apart, the acid is a weak acid. Weak acids include acetic acid, citric acid, and carbonic acid. Chapter 15 Section 3 Solutions of Acids and Bases

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Strengths of Acids and Bases, continued Strong Versus Weak Bases When all molecules of a base break apart in water to produce hydroxide ions, OH -, the base is a strong base. Strong bases include sodium hydroxide, calcium hydroxide, and potassium hydroxide. When only a few molecules of a base break apart, the base is a weak base, such as ammonium hydroxide and aluminum hydroxide. Chapter 15 Section 3 Solutions of Acids and Bases

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids, Bases, and Neutralization The reaction between acids and bases is called a neutralization reaction. Acids and bases neutralize one another because the hydrogen ions (H + ) in an acid and the hydroxide ions (OH - ) in a base react to form water, H 2 O. Other ions from the acid and base dissolve in the water. If the water evaporates, these ions join to form the compound called a salt. Chapter 15 Section 3 Solutions of Acids and Bases

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids, Bases, and Neutralization, continued The pH Scale An indicator, such as litmus, can identify whether a solution contains an acid or base. To describe how acidic or basic a solution is, the pH scale is used. The pH of a solution is a measure of the hydronium ion concentration in the solution. The next slide shows the pH values for many common materials. Chapter 15 Section 3 Solutions of Acids and Bases

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 3 Solutions of Acids and Bases

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acids, Bases, and Neutralization, continued pH and the Environment Living things depend on having a steady pH in their environment. Some plants prefer acidic soil with a pH between 4 and 6. Other plants need basic soil with a pH between 8 and 9. Many organism living in lakes and streams need a neutral pH to survive. Chapter 15 Section 3 Solutions of Acids and Bases

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Salts When an acid neutralizes a base, a salt and water are produced. A salt is an ionic compound formed from the positive ion of a base and the negative ion of an acid. Sodium chloride, commonly known as table salt, is one example of a large group of compounds called salts. Chapter 15 Section 3 Solutions of Acids and Bases