Teaching acids and bases in high school chemistry? Hands-on demonstrations can bring abstract concepts to life for students! These engaging acid-base demos will enhance your lessons and help students grasp key ideas like pH, indicators, and neutralization reactions. Try these in your classroom to spark curiosity and deepen understanding.
1. Arrhenius Acid-Base Theory
In this lesson I teach my students the difference between acids and bases and their properties.
- Bond Type: Acids have covalent bonds and are ionized by water. Bases have ionic bonds and dissociate in water.
- Taste: Acids taste sour and bases are bitter
- pH values (we don’t touch much on this right now)
- Special ion in solution: For acids thats, H+ and in bases it’s OH-
- Forms an electrolyte
Demo: Your students should already know that ionic stuff dissolved in water is going to create an electrolyte. But acids are weird. Because they have covalent bonds, but still break apart into ions in solution! Use a conductivity tester to show how acids conduct electricity in water. Compare this to other covalent things that can dissolve in water. Like sugar. This classic acid base demo reinforces the Arrhenius definition by showing that acids and bases increase the concentration of ions in solution.
2. Brønsted-Lowry Acid-Base Theory
Bronsted Lowry acid base theory just expands on the Arrhenius definition and that’s the focus of this lesson. Some weird things like ammonia can have a reaction with water and force WATER to be the acid or the base. Now again, my students don’t know much about pH or indicators at this point. Just what they remember from middle school. So I make sure to let them know that adding phenolphthalein to a solution and seeing it turn pink indicates we are working with a base.
Demo: Write the formulas and Lewis Structures for 3 compounds on the board. I like HCl, NaOH, and NH3. (You could choose any other acid or base, really.) Then I make sure my students identify that HCl is the acid, NaOH is the base and we are left undecided on NH3. So we then test with phenolphthalein. HCl – clear. NaOH – pink. NH3 we are SURPRISED that it’s pink because there’s no OH-! I then write out the equation of ammonia and water and boom, we can see that WATER supplied the hydroxide. This potentially my favorite of all the acid base demos.
3. Naming Acids and Bases
Unfortunately, I don’t have a demo for this lesson. There isn’t really a crafty way to introduce this concept. If you’ve got something, email me and let me know! Here’s how I teach the lesson though! I like to start with bases, since my students will already know how to name ionic compounds. So we do a quick review and practice naming some bases. Naming acids is a little trickier because it’s something new. So we’ll go over naming binary acids and then ternary acids that contain polyatomic ions. I’ve got a worksheet that you can get for free on naming acids and bases. This worksheet would be great for sub plans on the chance that you are out sick.
4. pH Scale
The pH scale was definitely taught to your students in middle school. But now is the time to teach them the inverse relationship of the concentration of H+ in the solution and the pH of the solution. Even though my students aren’t doing pH calculations, I expect them to know HOW the scale works. So by the end of the lesson, my students will know that a solution with a pH of 1 is 10 times more acidic than a solution with a pH of 2. The demo for this should be based in DRAWING this out before “mathing” it.
Demo: Draw two beakers. Draw an equal number of “water molecules” in each beaker. (I say it like that because I just draw circles and call it water.) Then in one of them, draw just one circle in another color to represent hydrogen ion. The second beaker should get ten of these circles. Going with this imaging, you can then better explain how the math makes sense for the pH scale. I like to focus on the multiplying and dividing aspect. Going DOWN the pH scale, the hydrogen ion concentration increases. So to go from the first (1 circle) beaker to the second (10 circle) beaker you are going DOWN the scale and increasing concentration ten-fold.
5. Acid-Base Indicators
In this lesson, students learn that there are a lot of chemicals that can change their colors based on the presence of specific ions. Acid base indicators change color based on the presence of hydronium or hydroxide.
Demo: Now for this demo, you can use anything you like. If you want to spend some money spoiling your students, you can bring in some blueberry muffins. The blueberries can turn the muffins green-ish or purple-ish based on the pH of the surrounding area. Hydrangeas are similar too. They’re either pink, blue or purple based on the pH of the soil. (White hydrangeas don’t change color at all.) Last up, you can just test some regular old acid or bases with any indicator you like. I really like universal indicator for this because it has a beautiful range of colors to line up with the pH scale.
Typically, after this lesson is taught, I like to do my Red Cabbage Indicator Lab. In this lab, students are going to boil down red cabbage until they get a rich purple solution. This solution is an acid base indicator! Because the solution varies a bit from student to student due to the differing concentration of the cabbage, students must create a standard. So they test their indicator with solutions of known pH. Then they test a few solutions of unknown pH and compare them to the standard created. You can get the lab here, or get it inside the full year lab manual with 40 other lab activities for high school chemistry students.
6. Acid-Base Reactions – Neutralization and Acid + Metal
I teach two acid base reactions in this lesson. The first is neutralization. I focus a lot on that in the next lesson. For this lesson, the focus should be on the reaction between acid and a metal. This demo is a lot of fun:
Demo: Drop magnesium or zinc into hydrochloric acid, then collect the hydrogen gas in a test tube and ignite it for the classic “pop” test. It’s a lot of fun to hear the pop. Students really get a kick out of it. Plus it helps to make the situation much more concrete.
7. Titration
For this lesson, I teach the process of titration and the math that goes with it. I think the best way to really get a grasp on this concept is for students to do the titration themselves. no demo required! In my full year lab book, I have a lab activity on the titration of vinegar. (You can read more about the lab book right here.) Phenolphthalein is my favorite indicator, because it’s really easy to see when it changes. You really could do any acid-base combo and any indicator you have in your stockroom.
Bring Acid-Base Chemistry to Life!
These acid base demos will help your students engage with chemistry in a meaningful way. If you’re not interested in writing any curriculum for your acid base unit, check out mine! Included is 7 guided notes lessons with slides, practice worksheets, vocabulary resources and three versions of a unit test.
