Acid /Base Demonstration

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Objective

Students will be able to see the various pH values of eleven different solutions.

Big Idea

Demonstrating the different pH solutions to different solutions gives the students an opportunity to understand that all solutions have a pH that is either acidic, basic, or neutral.

NGSS Background

This lesson is based on California's Middle School Integrated Model of NGSS.

NGSS Performance Expectation (PE): (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 occured.

Science and Engineering Practice (SP) 4: Analyzing and Interpreting Data. Students will use the data available on different solutions to place the pH values on a scale.

Disciplinary Core Ideas (DCI): PS1.A: Each pure substances has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.

Crosscutting Concepts (CCC): Patterns - Solutions all have a specific pH value that is unique to their chemical composition. The students learn that pH forms a pattern in nature with some solutions giving away excess hydrogen atoms (acids) and other solutions accepting hydrogen atoms (bases).

This activity provides students with the background knowledge that all solutions have a measurable pH. If the pH is high (7-14) the solution is considered a base, if it exactly measured at 7 it considered neutral, and if it low (0-7) it is considered an acid. Student often mischaracterize a strong acid as something which could dissolve metal and flesh (thanks to references in movies like 'Alien'. The see that strong acids are in fact defined by their pH level. I treat this activity as an introduction to acids and bases and not a comprehensive lesson that exposes all facets of pH.

Set-up

15 minutes

Materials

  1. Small beakers (11)
  2. Digital pH meters (11)

Solutions

  1. Tap water
  2. Distilled water
  3. Orange juice
  4. Milk
  5. Ammonia
  6. Hydrogen peroxide (3%)
  7. Apple juice
  8. Vinegar
  9. Hydrochloric acid (toilet bowl cleaner)
  10. Liquid soap
  11. Artificial urine

The artificial urine is always a hit. To make it I add water, salt, ammonia, and several drops of yellow food coloring. To give just the right touch of authenticity I heat it up in the microwave for several seconds. I know it's gross and I always have to stress that it is artificial, but it sure makes for a fun day. You don't have to include it in your lab.

I lay out all eleven solutions and place labels on each beaker. I then insert a digital pH meter into each solution and allow the meter to calibrate to the solution.

Student Activity

30 minutes

This activity is really a demonstration of me writing down a giant pH scale on the board and inserting the solutions, along this their pH values, to that scale.

 

As I am recording the different solutions onto the board, the kids are making the same diagram in their Interactive Science Notebook. The purpose of this demonstration is to get the kids to realize that every solution has a pH value and they either fall into the neutral, acidic, or basic category.

I end the lesson with Phet pH Scale Simulator. It gives the kids a chance to manipulate pH in a safe environment. We have a class set of Chromebooks and the kids visit the pH simulator and manipulate the solutions for a few minutes. To get everyone to the same website quickly I print up QR Codes that the kids can use the Chromebook's cameras and a QR Code Reader App to get to the requires site. Here's the QR code that I use.

QR Code Generator

Phet Simulator (QR Code) - pH Scale

I explain how to use the simulation with students in this video.

Student Work Sample