1. Acids and Bases and the pH Scale

2. Some of our favorite foods make our tongue curl up because they are SOUR. Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases

3. Some foods have a “bite” of their own because they’re somewhat bitter. Some foods have a “bite” of their own because they’re somewhat bitter. Acids and Bases Why?

4. There is a scientific reason for this: There is a scientific reason for this: These foods are either acidic or basic! These foods are either acidic or basic! Other substances besides foods have these characteristics, such as chemicals Other substances besides foods have these characteristics, such as chemicals Things that are neither acids nor bases are neutral Things that are neither acids nor bases are neutral Acids and Bases

5. Acid Characteristics Often taste sour Often taste sour Can burn skin & eyes Can burn skin & eyes Strong acids can dissolve metals Strong acids can dissolve metals Examples: Examples: Lemon juice Lemon juice Vinegar Vinegar Car battery acid Car battery acid (dangerous!)

6. Base Characteristics Can taste bitter, sweetish, or salty Can taste bitter, sweetish, or salty Strong bases can burn skin & eyes Strong bases can burn skin & eyes Often used for cleaning Often used for cleaning Examples: Examples: Milk Milk Baking soda Baking soda Soap Soap Drain cleaner Drain cleaner (dangerous!)

7. Some substances are not really an acid or a base: For example, pure water Some substances are not really an acid or a base: For example, pure water

8. The number of hydrogen ions a substance has (H+) The number of hydrogen ions a substance has (H+) The more hydrogen ions a substance has, the more acidic it is The more hydrogen ions a substance has, the more acidic it is The fewer hydrogen ions a substance has, the more basic it is The fewer hydrogen ions a substance has, the more basic it is How Do We Measure Acidity and Basicity?

9. The pH Scale! The pH Scale! “p” stands for potential and “H” stands for hydrogen; hence, the potential of a substance to attract hydrogen ions “p” stands for potential and “H” stands for hydrogen; hence, the potential of a substance to attract hydrogen ions pH is measured using special strips of paper called pH paper pH is measured using special strips of paper called pH paper How Are Hydrogen Ions Measured?

10. How Does It Work? The paper is treated with chemicals that change color to show the pH. The paper is treated with chemicals that change color to show the pH. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.

11. The pH Scale pH scale ranges from 0 -14 pH scale ranges from 0 -14 pH 7 is neutral; neither acid nor base pH 7 is neutral; neither acid nor base The closer to the ends of the scale, the stronger the solution is The closer to the ends of the scale, the stronger the solution is

12. Reading the pH Scale Any substance which has a pH of value of less than 7 is considered an acid Any substance which has a pH of value of less than 7 is considered an acid Any substance which has pH value greater than 7 is a base Any substance which has pH value greater than 7 is a base A pH of 7 is called neutral—neither acid nor base. A pH of 7 is called neutral—neither acid nor base.

13. Why is pH important? Soil has to be in a certain pH range for plants to grow and stay healthy. Fish can’t live if the pH is too high or too low

14. pH and People Our enzymes all work at an optimal pH If the pH of our bodies changes, our enzymes will no longer function, and that means death!