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Let's Learn Science: pH Meter Lesson Plan for 7th 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 learning more about cabbage chemistry in the following lesson plan.

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pH Meter.JPG

AMBF Collection Area: pH Meter

Grade: Middle School (recommended 7th grade)

Subject Area: Science, English Language Arts

Duration: 1-2 classes of 40 minutes

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 substances using a variety of pH testing methods
  3. Students will be able to explain how a chemical reaction is involved in pH scale testing with indicators
  4. Students will be able to make a pH indicator and use it to test the pH of various household solutions

Learning Standards

Next Generation Science Standards:

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

PS1.A Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants

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. Small red cabbage
  2. Pot of boiling water
  3. Strainer
  4. Small white Dixie cups (one for each solution you want to test pH of)
  5. Pipette
  6. Large bowls or pots (2)
  7. Notebook
  8. Various household solutions to test pH of
  • Fruit juices: lemon, lime, orange, apple, etc
  • Light colored soda
  • Vinegar
  • Baking soda solution
  • Anything!

9. Cabbage Chemistry Student Handout (available in the Printable PDFs section below)

Printable PDFs

Classroom Activities

  1. Warm-up Discussion: Make a list of drinks you enjoy and whether you think they are acidic or basic based on their taste/flavor.
  2. Pass out the Cabbage Chemistry Student Handout and read as a whole class or in pairs. Suggested comprehension questions:

● What is a pH scale?

● What pH number indicates an acid? base?

● When an indicator changes, is it an example of a chemical or physical change? How do you know?

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

4. 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 other household items or foods they would like to measure pH. Students will predict if they think they are acids and bases. Students will bring in a new substance to test and see if their hypothesis was correct.
  • Students divide into groups and explore the careers such as a chemist, doctor, nurse, food and beverage manufacturers, and chefs. Students will report back how these jobs depend on pH levels knowledge to best serve their customers.

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

Thank you to the following contributors and content curators of this lesson plan: Christopher Gear, Alison Mondrach, M. Ed., Scott Pawlowski, Kaerie Ray, Kelsey Talbot, Nicole Zawadzki, and Mariana Zechini.