1. Unit 5 Lesson 3 Measuring pH Copyright © Houghton Mifflin Harcourt Publishing Company

2. What’s Your Number? Copyright © Houghton Mifflin Harcourt Publishing Company What is the pH scale? The pH of a solution is a measure of how acidic or basic a solution is. A solution that has a pH value of exactly 7 is neutral—neither acidic nor basic. A solution with a pH value of less than 7 is acidic. There are more H 3 O + ions than OH – ions in the solution. A solution with a pH value greater than 7 is basic. There are more OH – ions than H 3 O + ions in the solution. Unit 5 Lesson 3 Measuring pH

3. What is the pH of some common solutions? Lemon juice has a pH of about 2. Milk has a pH of about 6.5, but sour milk has a pH of about 4. Pure water is neither acidic nor basic; it is neutral. It has a pH of 7. A solution of ammonia has a pH of around 12. Antacid tablets dissolve in water to form a basic solution of about pH 8. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

4. What is the pH of some common solutions? Locate lemon juice, milk, pure water, and ammonia on the pH scale. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

5. How is pH measured? An acid-base indicator is a dye that changes color at a certain pH range. The pH can be estimated by placing a few drops of indicator in a solution. The pH of a solution can be checked by placing a drop of the solution on a strip of universal pH paper, which contains several acid-base indicators. An electronic pH meter has a probe that is placed into the solution being measured. A precise pH value is measured. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

6. A Natural pH Meter Copyright © Houghton Mifflin Harcourt Publishing Company Hydrangea plants act as acid-base indicators in nature. The flowers change color depending on the pH of the soil. Pink flowers indicate that the soil pH is greater than 6.5. It is basic. Blue flowers indicate that the soil pH is less than 5.5. It is acidic.

7. In Our World Copyright © Houghton Mifflin Harcourt Publishing Company What role does pH play in the environment? If soil pH is too acidic or too basic, the nutrients plants need do not dissolve into the water in the soil. As a result, plants do not grow well, and the animal population that depends on the plants also suffers. The pH of ocean water is usually about 8. If the water absorbs too much carbon dioxide, the pH may be lowered, harming sea animals. Unit 5 Lesson 3 Measuring pH

8. What role does pH play in the environment? How would a decrease in soil pH affect the ecosystem shown? Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

9. What causes acid rain? Acid rain is any form of precipitation, such as rain, sleet, or snow, that has a lower pH than the normal range between 5 and 6. The burning of fossil fuels releases sulfur oxides and nitrogen oxides, which combine with water in the air to produce sulfuric acid and nitric acid. These acids in the atmosphere form acid rain when they dissolve in precipitation such as raindrops. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

10. What are the effects of acid rain? Acid rain can lower the pH of lakes, ponds, and streams, harming aquatic species and other organisms that rely on the water for survival. Acid rain can harm plants by damaging their leaves. It can also harm plants and other living things by lowering soil pH. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

11. What are the effects of acid rain? Acid rain can damage buildings and sculptures made of limestone and marble, by reacting with the stone. Acid rain can also damage paint and cause metals to corrode faster. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

12. Body in Balance Copyright © Houghton Mifflin Harcourt Publishing Company Where does pH play an important role in the human body? Stomach pH is usually about 2.5. But if food that is difficult to digest is eaten, more stomach acid is made and the acidity can drop as low as 1.2. Difficulty digesting food and a low stomach pH can cause discomfort called indigestion. Stomach pH can be restored back to a normal level by consuming antacid tablets, which are basic. Unit 5 Lesson 3 Measuring pH

13. Where does pH play an important role in the human body? To maintain good health, blood pH needs to be between 7.35 and 7.45. If blood pH falls below 7.35, it is too acidic. This condition is called acidosis. If blood pH rises above 7.45, it is too alkaline. This condition is called alkalosis. Both conditions make a person feel ill. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH

14. Where does pH play an important role in the human body? How does blood pH affect a person’s health? Copyright © Houghton Mifflin Harcourt Publishing Company Unit 5 Lesson 3 Measuring pH