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The pH of Soil (1 Favorite)

LAB in Observations, Interdisciplinary. Last updated April 3, 2019.


Summary

In this lab, students will determine and compare the pH of different types of soil from their school, homes, or neighborhoods. Students will then decide what types of plants can grow in acidic or alkaline soils.

Grade Level

Elementary School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • 2-PS1-2: Analyze data obtained from testing different materials to determine which materials have the properties that are best suited for an intended purpose.
  • 3-5-ETS1-2: Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.

Objectives

By the end of this lab, students should be able to

  • Understand the pH scale, and be able to interpret the meaning of a pH value.
  • Collect and record pH data from various soil samples.
  • Determine what types of plants can grow in neutral, acidic, or basic soils.

Chemistry Topics

This lab supports students’ understanding of

  • Acids & Bases
  • pH
  • Observations
  • Soil properties
  • Plant properties

Time

Teacher Preparation: 30 minutes

Lesson: 60 minutes

Materials

(per group)

  • 2 clear bowls or mason jars per soil sample
  • Two or three types of soil (1 cup each)
    • They can be 2-3 cups of soil from the schoolyard, your house, a nearby playground (for a more sandy soil), a garden, etc.
  • Labels and pens/markers to label the bowls or jars
  • ½ cup of Baking soda
  • 2 cups of Vinegar
  • 1 cup of Distilled water
  • Measuring cups, tablespoons and teaspoons

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • 2-4 students per group is suggested.
  • You can assign each student to bring in a quart Ziploc bag of soil from their house/garden/playground to use in this experiment.
  • You should have enough soil to do at least two tests per soil (one test is baking soda, one test is vinegar)
  • This can be done in groups or as a demonstration by the teacher.
    • If you do this as a demo, you will only need enough materials for one group.
    • This lesson can also be done with red cabbage instead of vinegar and baking soda.
    • This is a video of the experiment being done with baking soda and vinegar for teacher reference.
    • Home gardeners and farmers do tests like this to determine what sort of amendments they need to add to their soil to help plants grow.
    • If you have time and a lot of soil, you can let your students observe the soil and record notes (color, moisture, if there are clumps, particle size, etc.) about each of the samples.
    • For higher-level grades, you can include more information about soil amendments (i.e.: fertilizers, organic fertilizers, etc.) that farmers use to make the soil more hospitable for certain crops or plants.
    • For higher-level grades or for a longer lesson, you can incorporate lessons about acid rain and how that affects soil and crops.
    • This is a video that introduces soil in a fun and interesting way, but there is a lot of information here.
    • Answer Key for Pre-lab Questions:
      1. Soil: minerals, air, water, organic material
      2. pH acidic:1-6
      3. pH neutral: 7
      4. pH basic: 8-14
    • Answer Key for Analysis Questions:
      1. Answers will vary.
      2. Plants that can grow in acidic soils: apples, blackberries, eggplant, pepper, sweet potato, tomato
      3. Plants that can grow in neutral soils: carrots, celery, corn, lettuce, peas, radish
      4. Plants that can grow in basic soils: beets, cucumber, garlic, honeysuckle, pumpkin, summer squash
  • Two additional elementary school lab resources available in the AACT Resource Library that are focused on the chemistry of soil investigations are Settle that Soil and Soil Permeability.

For the Student

Background

We use pH to measure of how acidic or basic something is, in this case the pH of soil samples will be measured. Soils can basic, neutral, or acidic: the pH scale is 0-14 with 7 being neutral, anything below 7 is acidic, and anything above 7 is basic (also called alkaline). For example, orange juice has a pH of 3, ocean water has a pH of 8, and bleach has a pH of 13. In this experiment you’ll be using baking soda (pH = 9) and vinegar (pH = 2). Most soils, however, usually have a pH between 4.5-8.

Lab thephofsoil phscale

Plants need water, nutrients, and sunlight to grow, but they also need soil. Soil holds the roots of the plants in place as they grow, and stores the water and nutrients the plants need. It is important for farmers and gardeners to know the pH of their soil because it will help them determine what type of plants they can grow. Some plants can grow in more acidic soil, and some plants can grow in more alkaline (basic) soil. If you have a soil that is more acidic, you could grow blueberries but not asparagus. The pH of a soil will determine how easily plants can use nutrients they need to survive and grow.

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Pre-lab Questions

  1. What is soil?
  2. What is the pH scale for acidic soil?
  3. What is the pH scale for alkaline soil?
  4. What is the pH scale for neutral soil?

Objective

Are the soils from your neighborhood, school, and playground acidic, neutral, or basic? What type of plants could you grow in these soils?

Procedure

  1. You will need two jars or bowls and a soil sample.
  2. Measure ¼ cup (2 tablespoons) of the soil sample into one of the bowls or jars. Then measure ¼ cup (2 tablespoons) of the soil sample into the other bowl or jar.
  3. Label each jar or bowl with the location of where the soil is from (ex: playground) and the ingredient it will be combined with. One jar will be for Vinegar and the other for Baking Soda.
    • An Example of your final label: “Playground – Baking Soda.”
  4. For the vinegar test, add ½ cup of vinegar to the vinegar jar. If the soil fizzes or bubbles, your soil is basic.
  5. For the baking soda test, add ¼ cup of distilled water to your soil and stir so that it becomes muddy. Then, sprinkle 2 teaspoons of baking soda on top of the soil. If the soil bubbles right away, your soil is acidic.
  6. If your soil doesn’t fizz or bubble for either test, you have a neutral soil.
  7. Complete the data table below for each soil sample.
  8. Repeat these procedures for each soil sample that you test.

Data


Soil 1 Soil 2 Soil 3

Where is this soil from?




Did it react to vinegar?




Did it react to baking soda?




Is the soil acidic, alkaline, or neutral?




Analysis

  1. Were you surprised by the pH of each soil?
  2. Using the list below, what plants can grow in acidic soil?
  3. Using the list below, what plants can grow in alkaline soil?
  4. Using the list below, what plants can grow in neutral soil?
pH Levels for specific plant growth

pH of 4.5-6.5:

pH of 7:

pH of 7.5-8.5:

  • Apples
  • Pepper
  • Blackberries
  • Sweet potato
  • Eggplant
  • Tomato
  • Carrots
  • Lettuce
  • Celery
  • Peas
  • Corn
  • Radish
  • Beets
  • Honeysuckle
  • Cucumber
  • Pumpkin
  • Garlic
  • Summer squash

Conclusion

What did you learn about soil that you did not know before? Why do you think it is important to know the pH of soil? Give an example of how this information might be useful and who it could be useful for.