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Let's Learn Science: pH Meter Lesson Plan for 8th Grade

In 1934, Arnold O. Beckman was approached by a former classmate (Glenn Joseph) who asked him to create a sturdier and more reliable tool that could quickly measure the acidity of lemon juice for the California Fruit Grower’s Exchange (Sunkist). The pH meter that Beckman created uses an electrochemical process to determine the acidity or basicity of a sample by measuring the amount of electricity between two electrodes. Beckman added vacuum tube amplifiers which amplify weak electrical signals without distorting them, which allowed for thicker, stronger glass electrodes to be used in a more sensitive instrument. Then, he integrated all relevant equipment into one portable instrument. All one had to do was prepare a sample, insert the core, and read off the pH value. Beckman’s innovations launched an instrumentation revolution that made scientific measuring easier, cheaper, and more accurate.

We can better understand the importance of the pH meter and how it works by conducting the soil and water experiment in the following lesson plan.

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pH Meter.JPG

AMBF Collection Area: pH Meter

Grade: Middle School (recommended 8th grade)

Subject Area: Science, English Language Arts

Duration: 1.5 hours in class for first day; 30 minutes on second and third days (can be decreased by shortening experiment time)

Lesson Objectives

  1. Students will be able to define pH scale and share common acidic and basic substances with their pH number
  2. Students will be able to conduct an experiment to measure, record, and analyze the pH levels of soils using a variety of methods
  3. Students will be able to explain how different soil types affect water runoff pH level

Learning Standards

Next Generation Science Standards:

MS-LS2-3 Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.

MS-ESS2.C Water’s movements—both on the land and underground—cause weathering and erosion, which change the land’s surface features and create underground formations.

MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred

Common Core State English Language Arts Standards:

CCSS.ELA-LITERACY.RST.6-8.3 Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks

CCSS.ELA-LITERACY.RST.6-8.7 Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table)

Materials

  1. Three samples of soil from separate areas
  2. Small shovel or trowel for gathering soil samples
  3. Ruler, metric
  4. Gallon ziploc bags (3)
  5. Large Tupperware (9)
  • Small deli containers, like the kind sour cream or cottage cheese come in, also work.

6. Permanent marker

7. Small containers or cups, at least 3-oz. (3). They need not be identical.

8. Tap water

9. pH paper, with resolution of at least ±0.3 pH units and a range from 3 to 8 or a pH meter for liquids

  • You may need more than one set of pH paper to cover this range of pH values at ±0.3 pH unit resolution. See Table 2 in the Acids, Bases, & the pH Scale for more help.

10. Soil pH meter, with a pH range of at least 3.5 to 9 and a resolution of ±0.1 pH units

11. Facial tissues or cotton balls (10)

12. Clock, timer, or stopwatch

13. Duct tape

14. Coffee filters (18)

15. Lab notebook

Printable PDFs

Classroom Activities

  1. Warm-up Discussion: What value of pH is neutral? What ranges are acidic and basic? Can you think of examples of ways in which the geosphere, biosphere, and hydrosphere interact with each other? What is runoff water and why might it matter what the pH of that water is? How do scientists identify different soil types?
  2. Pass out the Acids and Bases Experiment Student Handout (available in the Printable PDFs section above) and read as a whole class or in pairs. Have students try to define in their own words the following terms:

● pH

● Neutral pH

● Acidic

● Alkaline or basic

● Geosphere

● Biosphere

● Hydrosphere

● Runoff water

● Soil types

● Soil texture

3. Run through the experiment to demonstrate how to use the pH meter on the soils and pH paper on the water runoff.

4. In groups, have students follow the instructions and complete the lab recording their results in the table and answering the questions.

5. As a whole class, discuss results and share as a class:

● What surprised you today?

● What is something new you learned?

Extension Ideas

● Students list what types of soil would be best for growing plants and vegetables, whether or not they think more acidic or basic soil is best.

● Introduce fertilizer into the soils to see if the pH levels change.

Additional Resources // Recursos adicionales

Read more about the pH Meter here or watch the video below.

MEDIDOR DE PH

En 1934, un ex compañero de clase (Glenn Joseph) se aproximó a Beckman y le pidió que desarrollara una herramienta más resistente y confiable que pudiera medir rápidamente la acidez del jugo de limón para la California Fruit Grower's Exchange (Sunkist). El medidor de pH que creó Beckman utiliza un proceso electroquímico para determinar la acidez o basicidad de una muestra midiendo la cantidad de electricidad entre dos electrodos. Beckman agregó amplificadores de tubo de vacío que amplifican las señales eléctricas débiles sin distorsionarlas, lo que permitió el uso de electrodos de vidrio más gruesos y fuertes en un instrumento más sensible. Luego, Beckman integró todo el equipo necesario en un instrumento portátil. Todo lo que tenía que hacer un químico era preparar una muestra, insertar el núcleo y leer el valor de pH. Las innovaciones de Beckman iniciaron una revolución instrumentista que volvió a la medición científica más fácil, barata y precisa.

Sources // Contributors

This lesson plan was developed using inspiration and some source material from here. Thank you to the following contributors and content curators: Christopher Gear, Alison Mondrach, M. Ed., Scott Pawlowski, Kaerie Ray, Kelsey Talbot, Nicole Zawadzki, and Mariana Zechini.