Using AACT Resources to Teach Acids and Bases
By Kim Duncan on May 10, 2018
As chemistry teachers plan activities for their students, AACT will highlight resources from our high school library that help to reinforce topics in different units throughout the school year.
In our last news post, we looked at classroom resources that focused on equilibrium. Now we are moving on to lessons and activities that can be used to support a unit plan for teaching acids and bases. This includes pH, acid theories, strong versus weak acids and bases, titrations, indicators, and buffers.
Introduce the unit with the Acid & Base Guys video which tells the story of how the definition of acids and bases evolved from Lavoisier’s hypothesis that acidity is caused by oxygen atoms, to Arrhenius’s definition of an acid as a producer of positive hydrogen ions, then changed to acids as proton donors by Bronsted and Lowry, finally switching to acids as electron acceptors by Lewis.
The lab, Exploring the Properties of Acids and Bases allows students to investigate the properties of acids and bases through testing a variety of household substances in a five station activity. By the end of this lab, students will be able to differentiate between acids and bases and identify the properties of each.
Use the lesson plan, Calculating pH, A Look at Logarithms to teach your students about the base-10 logarithmic scale and then use it to calculate pH from hydrogen ion concentration. Often students are able to calculate pH by pushing the correct buttons on their calculators, but they don’t understand what the values mean. By the end of this lesson, students will be able to explain why we use logarithms to express pH, estimate pH value from hydrogen ion concentrations, use a calculator to calculate pH, and classify a substance as acidic, basic, or neutral.
After students learn how to calculate pH, use Categorizing, Calculating and Applying Concepts from Weak Acids, Weak Bases and Salts to help them write dissociation reactions and make connections between conjugate acid-base pairs, pH, salts, and the equilibrium constant. They then use a beaker diagram activity to help further understand the properties of weak and strong acids and bases. This lesson includes several activities that can be used alone or in sequence.
Use the demonstration, How to Perform a Titration to show your students how a titration is set-up and performed. This will teach them how to put together the equipment for a titration, accurately follow the steps to perform it, determine which indicator should be used, and use data collected to calculate the molarity of an unknown substance.
Follow the demonstration with a lab, Titration Curves, which allows your students to graphically observe the plot of acid/base titrations and determine the equivalence point of each. This microscale lab includes four parts: Strong Acid/Strong Base, Weak Acid/Strong Base, Strong Acid/Strong Base, and Weak Acid/Strong Base.
We have several acid-base titration labs in the AACT Resource library. The Lethal Dose lab allows students to calculate the concentration of a potentially “lethal” solution through titration. You could also use the lab, Calculating Acid in Lemon-Lime Soda to have your students investigate the molarity of citrus acid in different soft drinks. Currently, our most “favorited” titration resource is the Egg-straordinary Issue lab which has students determine the percent composition of calcium carbonate contained in an eggshell.
Introduce the concept of buffers with the card sorting game included in the activity, What are Buffers? By the end of it your students will be able to write chemical equations for the reaction of a strong acid and strong base as they are added to a buffer solution and also be able to explain how a buffer is able to resist changes in pH.
Finally, use the lesson plan, Preparation and Evaluation of Buffers to teach your students multiple methods to calculate and prepare buffered solutions of a desired pH. This lesson plan also includes a formative quiz with an answer key and a PowerPoint presentation to use with your classes. Additionally, it includes alignment with three AP Chemistry learning objectives.
We hope that these activities can help you to reinforce several of the topics covered in a unit about acids and bases. Most of these lessons were made possible by great teachers who shared their own resources. We need your help to keep the collection growing. Do you have a great demonstration, activity, or lesson related to this topic that you would like to share with the community? Please send it along for consideration.