UC Irvine FOCUS! 5 E Lesson Plan Title: Acid/Base-pH Lab Grade Level and Course: 8 th grade Physical Science, Grades 9-12 Chemistry Materials:

Transcription

1 UC Irvine FOCUS! 5 E Lesson Plan Title: Acid/Base-pH Lab Grade Level and Course: 8 th grade Physical Science, Grades 9-12 Chemistry Materials: Detergent-quart, shampoo- quart Lemon-juice-quart Vinegar quart Milk-quart Orange-juice-quart Tomato-juice-quart Baking-soda Salt-shaker Peroxide-quart Pickle juice Apple-juice Containers-plastic-25 Liquid Plumber distilled water Rubber gloves eye droppers station signs Litmus paper blue/red acid rain paper towels Markers ph chart antacid tablets ph paper large containers transparent containers Safety glasses Pepto Bismol aprons Instructional Resources Used: (concept maps, websites, think-pair-share, video clips, random selection of students etc.) (virtual demo: Gems Alien Juice Bar) Use either a power-point, video or demo that will help student to become familiar with acids, basic, and neutral solutions. Also it allows students to understand what a ph scale is, and the ph value of indicates. Cooperative learning Many of the activities in this book employ group work and cooperative learning. Cooperative activities provide opportunities for students to exchange, write, and present ideas. Students will work in groups of 3s to 4s to identify the ph level of compounds. California State Standards: Grade 8 Physical Science: 5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept: e. Students know how to determine whether a solution is acidic, basic, or neutral. Grades 9-12 Chemistry: 5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept: d. Students know how to use the ph scale to characterize acid and base solutions. Lesson Objectives: This activity is designed for students to identify the ph level of compounds. By testing common household substances will help them: To understand the property of acid and base and how to test the ph of a liquid;

2 To relate the ph scale to how acidic or basic a solution is. Differentiation Strategies to meet the needs of diverse learners: English Learners: KWL -Have students construct a KWL chart about acids and bases, with the three column titles: What I Know about Acids/Bases ; What I Want to Know about Acids/Bases ; and What I Learned about Acids/Bases. Students will write in the appropriate columns before, during and after doing this lab. Encourage students to use illustrations. Special Education: KWL strategy for the EL and also be used for special needs students. GATE: Have students to research about the sources and causes of acid rain. (Acid rain is through to be due principally to the release of sulfur oxides and nitrogen oxides into the atmosphere). Follow by two questions: 1. How do weather patterns affect the distribution of environmental damage due to acid rain? 2. What types of conservation efforts are used to adjust the ph of lakes and rivers that become too acidic? ENGAGE Describe how the teacher will capture the students interest. Have students participate in the interactive virtual minilab that will challenge the students to learn about acids and bases. Challenge #1 Learn about acids and bases. After viewing this virtual interactive activity have students discuss the following questions. What kind of questions should the students ask themselves after the engagement? 1. What was the purpose of the cabbage juice? 2. What colors were used to indicate the presence of an acid, base and neutral solution? EXPLORE Describe the hands-on laboratory activity that the students will be doing. Students will determine whether the test substances are acids or bases, compare ph and litmus paper as it relates to the test results. List the big idea conceptual questions that the teacher will ask to focus the student exploration. 1. From the data collected, what generalization can you make about the ph of a solution, and the effect of a solution on litmus paper? 2. For the following solutions, how would you describe the H30 +

3 concentration? Label them as acidic, basic, neutral. Solution A ph 10 Solution B ph 7 Solution C - ph 3 EXPLAIN What is the big idea concept that students should have internalized from doing the exploration? Acids and bases are defined by the amount of hydronium (H30 + ) and hydroxide ions (H0 -) that are present. Water is neutral because it has the same number of hydronium ions and hydroxide ions. A ph scale indicates, with numbers, the concentration of hydrogen ions in a solution and characterizes a solution as acidic (lower than 7), basic (higher than 7), or neutral (near 7). List the higher order questions that the teacher will ask to solicit student explanations for their laboratory outcomes, and justify their explanations. 1. Explain why some substances are acids and some substances are bases. 2. What does it mean to say that distilled water is neutral? What ph should it have? EXTEND Explain how students will develop a more sophisticated understanding of the concept. As an extension students may demonstrate a neutralization reaction. Students should now be aware that acids have a ph of between 1-6. Stomach acid has a ph of about 3. Select the most acidic solution of those tested in class that mostly resembles stomach acid (which will be the lemon juice). Students should use the Internet in class to research the topics Acid Reflux and Heartburn. Have them locate over the counter medications such as Tums and Rolaids that are used to treat these conditions, and explain how they chemically balance or "neutralize" the ph of areas affected by heartburn. Heartburn is caused when stomach acid regurgitates into the esophagus, causing a lowering of the ph of the esophagus. This results in a burning sensation in the chest of a person with heartburn. Students may crush Tums or Rolaids into a sample of lemon juice. Students should then retest the ph of the Lemon Juice/Rolaids or Tums Mixture. If the ph has in fact increased, students should be able to determine if the medicine is effective in the treatment of heartburn. Have students explain their findings in their formal lab report. How is this knowledge applied in our daily lives? The ph inside most living cells is close to 7. Because the chemical processes of the cell are very sensitive to ph, even a slight change in ph can be harmful. Human blood, for example, is normally maintained at a ph very close to 7.4. A person cannot survive for more than a few minutes if the blood ph drops to 6.8 or rises to 7.8. Chemical processes ensure that the ph of blood is kept near 7.4. EVALUATE How will the student demonstrate their new understanding and/or skill?

4 Students will know how to determine whether a solution is acidic, basic, or neutral. What is the learning product for the lesson? o Using the data from this investigation, design a ph scale by listing the name and the ph of the substances tested. o Students will completely and accurately fill in all laboratory data. Background Knowledge for the Teacher: Indicators that change color are routinely used to determine whether a solution is acidic, basic, or neutral. A ph scale indicates with numbers the concentration of hydrogen ions in a solution and characterizes a solution as acidic (lower than 7), basic (higher than 7), or neutral (near 7). There are electrodes and electronic instruments that can measure directly the ph of a solution. Some acids and bases are defined other than by their hydrogen ion concentration, but they will be addressed in high school chemistry. Pure water has the same number of hydronium ions (H30 + ) as hydroxide ions (H0 - ), so it is considered neutral. 2H H H - Sources: Chemistry Lesson Plans- Middle school grades 6-8, Minnesota Science Teaching Education Project, Science Framework for California Public Schools, for Kindergarten through Grade 12, Student pages are attached.

5 Acid/Base-pH Lab Lesson Objectives: This activity is designed for students to identify the ph level of compounds. By testing common household substances will help them: To understand the property of acid and base; and how to test the ph of a Liquid. To relate the ph scale to how acidic or basic a solution is. Materials: Detergent-quart, shampoo- quart Lemon-juice-quart Vinegar quart Milk-quart Orange-juice-quart Tomato-juice-quart Baking-soda Salt shaker Peroxide-quart Pickle juice Apple-juice Containers-plastic-25 Liquid Plumber distilled water Rubber gloves eye droppers Electronic ph meter Litmus paper blue/red acid rain paper towels Markers ph chart antacid tablets ph paper large containers transparent containers Safety glasses Pepto Bismol aprons Procedure: Acid and Base Classification ph paper testing: 1. Obtain a 12-well plate. Note that each well is identified by a number for each substance that will be tested. Add a few drops of each substance into the wells on the plate. 2. For the indicator papers, dip the paper into the solution and record the color. For the ph, use the color chart provided with the ph paper to determine the ph of solution and record that value on your table. If the result is between two numbers, estimate to the nearest tenth. If an electronic ph meter is available, use it to test the ph of all test solutions. 3. Record your results in the data Table. 4. Rinse the glass rod with distilled water and proceed to test the other substances. Record these results in the data table. After all substances have been tested with ph paper, test each substance with red and blue litmus paper.

6 Litmus paper Testing: 1. The litmus paper has only two colors: red and blue. Red litmus turns blue in the presence of bases; blue litmus turns red in the presence acids. 2. Use a glass rod to touch one drop of a test substance to a strip of red litmus paper. If the red litmus paper turns blue, this is positive (+) for the presence of a base. If the red litmus paper remains blue, this is negative (-). Record the litmus results in the data table. 3. Use a glass rod to touch one drop of a test substance to a strip of blue litmus paper. If the blue litmus paper turns red, this is positive (+) for the presence of an acid. If the blue litmus paper remains blue, this is negative (-). Record the litmus results in the data table. 4. Finally, in the data table, classify each of the substances as an acid, base or neutral. Testing unknown solutions: 1. Obtain to unknown solutions and place in well number 11 and 12. Add a few drops of each substance into the wells on the plate. 2. Test the unknowns by using testing procedure for ph paper and Litmus paper. Record your results in Data table. Results Data Table Solution ph paper Red litmus Blue litmus Acid/Base/Neutral

7 Unknown 12. Unknown Analysis Questions: 1. Explain why some substances are acids and some substances are bases. 2. What does it mean to say that distilled water is neutral? What ph should it have? 3. List all substances tested and classify each as an acid or a base. Were any substances neutral (or nearly so)? 4. Consider the food items tested. What conclusions, if any, can you make concerning their ph? What conclusion can be made about the cleaning products in general?

8 5. From the data collected, what generalization can you make about the ph of a solution and the effect of a solution on litmus paper? 6. For the following solutions, how would you describe the H30 + concentration? Label them as acidic, basic, and neutral a. Solution A ph Using the data from this investigation, design a ph scale by listing the name and the ph of the substances tested.