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Acids and Bases Lesson Plan

Chemistry Lesson Plans

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These pH paper test strips were made using coffee filters dipped in red cabbage juice.

These pH paper test strips were made using paper coffee filters that had been cut up into strips and dipped in red cabbage juice. The strips can be used to test the pH of common household chemicals.

Anne Helmenstine

Acids, bases and pH are core chemistry concepts that are introduced in elementary level chemistry or science courses and expanded upon in more advanced courses. This chemistry lesson plan covers essential acids and bases terminology and offers students hands-on experience testing common home chemicals to determine whether they are acids, bases or neutral.

Introduction

Objectives

Time Required

This lesson can be completed in 1-3 hours, depending how in-depth you decide to get.

Educational Level

This lesson is best-suited for students at the elementary to middle school level.

Materials

  • red (purple) cabbage
  • coffee filters
  • household chemicals with a variety of pH levels. You can use this pH scale for ideas. Good choices include diluted ammonia, laundry detergent, milk, vinegar, water, soft drinks and lemon juice.
You may wish to prepare pH test strips in advance or this may be completed by the students. The simplest way to prepare test strips is to heat red cabbage leaves with a very small amount of water either in a microwave or else over a burner until the leaves are soft. Allow the cabbage to cool and then score the leaves with a knife and press coffee filters onto the cabbage to absorb the juice. Once a filter is completely colored, allow it to dry and then cut it into strips.

Acids and Bases Lesson Plan

  1. Explain what is meant by acids, bases and pH. Describe characteristics that are associated with acids and bases. For example, many acids taste tangy. Bases often feel soapy when rubbed between your fingers.
  2. List the materials that you've gathered and ask students to predict, based on their familiarity with these substances, whether they are acids, bases or neutral.
  3. Explain what is meant by a pH indicator. Red cabbage juice is the indicator used in this project. Describe how the color of the juice changes in response to pH. Demonstrate how to use pH paper to test pH.
  4. You can prepare pH solution or strips in advance or make this into a class project. Either way, have students test and record the pH of a variety of household chemicals.

Assessment Ideas

  • You may wish to provide an "unknown" and have students determine approximate pH. Based on the pH, is this an acid or a base? From a list of three chemicals with different pH values and characteristics, ask students to select the identity of the "unknown" sample.

     

  • Have students research pH indicators and identify other common household chemicals they might use to test pH instead of using red cabbage juice.

     

  • Ask students to explain, in their own words, the difference between acids and bases. What is meant by "neutral"? What does pH measure?

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