Lesson Plan Template: General Lesson Plan
Learning Objectives: What should students know and be able to do as a result of this lesson?
Students will be able differentiate between acids and bases.
Students will be able to describe the pH scale and three methods of measuring pH.
Students will be able to test a substance to determine if it is an acid or base.
Prior Knowledge: What prior knowledge should students have for this lesson?
Knowledge of the reaction between vinegar and baking soda
Familiarity with the terms: acid and base
Lab Safety Procedures for the classroom
Guiding Questions: What are the guiding questions for this lesson?
What is an example of an acid?
Vinegar, Coca-Cola, Orange Juice, Lemon Juice
What is an example of a base?
Baking soda, Windex, Dishwasher Detergent, Soap, Bleach
How are acids and bases measured?
The pH scale: from 1-14 (acids are low, bases are high, seven is neutral).
Teaching Phase: How will the teacher present the concept or skill to students?
Instructor will introduce the lesson by briefly reviewing the pH scale:
- The pH scale measures the strength of acids and bases
- The pH scale is from 0-14, with 7 being neutral (pure water)
- The pH scale has no units
- Acids are low on the pH scale, bases are high
Then he or she will explain how pH indicators work (they are different colors at different pH levels). For example, litmus is red in acidic conditions (low on the pH scale) and blue in basic conditions (high on the pH scale).
Next, the instructor will set out beakers of 3 different substances: a baking soda and water mixture, orange juice, and vinegar and ask students to predict what color the indicator will be (blue or red) and why they predict that. Remember, have students explicitly state their reasoning.
Finally, the instructor will add the indicator to the substances, allowing students to see whether their predictions were correct or not.
Instructor will facilitate note-taking and discussion using a PowerPoint presentation. Said presentation should include the aforementioned tenets of the pH scale, common examples of acids and bases, and the three ways to measure pH (liquid indicator (such as was used in the demo), pH paper, and pH meters).
Instructor will pose the question: which of the three ways to measure pH is the most accurate and why? Student answers will vary, but eventually students should come to the conclusion that since the pH meter directly gives the numeric answer it is more precise than the other two methods which involve matching colors to numbers. Why is color matching less accurate in your opinion? Have students give their opinion. Point out the fact that some people are color blind, and that this method is objective and open to interpretation.
Introduction to Acids and Bases
Guided Practice: What activities or exercises will the students complete with teacher guidance?
Instructor will demonstrate how to use the liquid pH indicator, pH paper, and pH meter and will then have each student group measure the pH of pure water using each of the three methods (to practice using the three methods as well as to check the calibration of the measuring tools). Students will then be required to create their own data table, listing the four different substances they will be measuring (lemon juice, bleach, dishwasher detergent, and soda) including three blanks for each of the three different methods they will use to measure the pH of each substance.
Be sure you are explicit when giving directions. It is a good idea to review lab safety procedures that is expected to be upheld in the classroom. Students should not wear open toed shoes or flip flops, long hair should be tied back and sleeves rolled up. Goggles should be worn when working with liquids and chemicals. Remind students that they are working with glass, and need to be cautious. If glass does break, they must inform the instructor and do not attempt to clean it up or touch the broken glass. Students should not run or yell in the lab. Explain to students that they should never smell or taste lab materials and need to wash their hands after they have cleaned up their station. Materials should be returned to the designated areas given by the instructor.
Independent Practice: What activities or exercises will students complete to reinforce the concepts and skills developed in the lesson?
Students will then be asked to measure and record the pH of four different substances (lemon juice, bleach, dishwasher detergent (preferably clear), and soda) using the three different methods and record the results in their data table.
Example Data Table
*Teachers: be sure to do the lab before hand to get a teacher's copy of the data. It is best if you do it with the same equipment the students will be using.
Closure: How will the teacher assist students in organizing the knowledge gained in the lesson?
As a class, discuss what pHs were found for each substance, what an acceptable margin of error might be, and what method of measurement was the most accurate and which was the least. Then create a list of household substances that students are curious about their pH (past answers have included: mouthwash, shampoo, alcohol, etc.) and assign each student one or two substances to research for homework or an additional assignment. The instructor has the option to collect the data recorded as a grade.
Next class when the students bring their homework in, teachers can spend a few minutes having the students present their research. Tell students that part of the assignment is to bring in a picture (from online, magazine, etc.) of their item. Students will post their item on a pH scale that you can post on the wall. Students can see where different household items fall. After students present, have them spend 5-7 minutes on a "Stop and Jot," which can be a few sentences (3-5 sentences) about what they have learned and if there are any further areas they would like to study/questions they may still have. Be sure to explicitly emphasize the importance of homework and tell students that they will be graded on the research, mini presentation, having the photo and their stop and jot. All must be completed for full credit.
Instructors may choose to evaluate students completed data tables, or require students to write a summary of their notes (including the lab).
Instructor will begin by asking "What do you already know about acids and bases?" [Student answers will vary but they should know acids can burn you, and bases may seem less harmful than acids, but they can still harm you if mishandled incorrectly]. Ask the class if they know what will happen when you mix baking soda and vinegar. Most of the students should be able to recall that it creates a reaction. Explain to the class that it does create a reaction between an acid and a base. Which of the two would be the acid? Have students raise their hand and give their answer with an explanation. Always have students explain their reasoning. Why would you say vinegar is the acid? I thought acids burn people? Make the point that acids and bases are found in many household items, and that acids are not always dangerous chemicals that cause your skin to burn.
Instructor will then ask "How are acids and bases measured?" [This question is to gauge how much students remember from previous science classes. Some students may not have an idea, so try to pose questions or comments that would lead them to recall the pH scale. Some students may remember once you mention it, but all should know at least a small amount about the pH scale from previous classes, or at least heard of it.]
From student answers to these questions, instructor will be able to determine the depth needed to be covered on each topic rather than focusing on topics students already know.
Feedback to Students
In the "teaching phase" of the lesson, students will be provided immediate feedback to their predictions about the acidity/basicity of three substances when the indicator is added. During the Guided Practice portion of the lesson, students will be provided feedback as to whether they are performing the measurement techniques successfully or not by the instructor (who will be walking around the room). The instructor will also be providing immediate feedback regarding the creation of data tables, guiding students to one of several possible correct layouts. Finally, students will receive feedback regarding the quality and precision of their pH measurements during the class discussion during the closure section of the lesson.