Using AACT Resources to Teach Aqueous Solutions

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 resources that focused on phase changes and heat transfer. Now we are moving on to lessons and activities that can be used to support a unit plan for teaching aqueous solutions. This includes molarity calculations, solution preparation, dilution, solubility, solubility rules, and colligative properties.

Start the unit with the demonstration, What is a 1 Molar Solution? Students complete short pre-lab questions and then watch the teacher create one, two, three, and half “molar” solutions using large beakers and plastic mole cutouts. This demonstration supports students’ understanding of solutions, the mole concept, as well as molarity and will help students determine the molarity of different solutions. The teacher then demonstrates how to make a one molar solution of a salt using the correct laboratory technique with a volumetric flask.

The Particle Level Molarity activity introduces students to molarity at the particle level. Students use their knowledge of molarity by preparing several Kool-Aid drinks, and then apply that information to create representations at the particle level. By the end of this activity, students will be able to explain the meaning of molarity while giving reference to the particle concentration in a solution, use models to represent the meaning of molarity, and calculate the molarity of a solution.

Use the Kool-Aid lab to have your students calculate the mass of Kool-Aid powder required to make three solutions (C₁₂H₂₂O₁₁) with different concentrations. This lab will help students explain the concept of molarity and calculate the number of grams of solute that are required to produce a given molarity of solution. Then use the Molarity of A Solution lab to teach your students how to perform dilutions of Kool-Aid and juice solutions. Students will calculate the amount of solute required to create a solution of a particular concentration and the amount of solvent required to dilute a concentrated solution.

Introduce the concept of soluble and insoluble substances using the Solubility Animation, which gives students the opportunity to visualize, on the particulate level, how solubility works. Examples of ionic compounds and molecular compounds show how when water molecules are attracted to charged parts, substances dissolve, and when they are not attracted to charged parts, they do not dissolve.

The Physical Properties lesson allows students to investigate how intermolecular forces affect physical properties by investigating melting point as well as solubility. This lesson helps students recognize that physical properties are related to intermolecular forces and understand how solubility works.

In the lab, What’s the Solution? students choose one factor that can affect the rate at which a solute will dissolve in solution, such as the amount of stirring, temperature, or particle size. They then design a procedure that can be used to determine how the variable will affect the rate of dissolution. Students use scientific methods to solve investigative questions, plan and implement investigative procedures, and determine which factor influences the rate of dissolution most: temperature, agitation, or surface area.

Before learning about the solubility rules, use the Net Ionic Equations Animation to show students a precipitate reaction on the particulate level and understand what a net ionic equation represents for this reaction type. Mixing two aqueous reactants that yield aqueous products and mixing two aqueous reactants that yield a precipitate are both part of the animation.

Use the Ions in Aqueous Solution Presentation to introduce the solubility rules to your students. In the lab portion of this classroom resource, students mix ionic solutions to determine what combinations form precipitates. They then deduce which ions are responsible for the precipitate and write overall equations and net ionic equations.

Introduce the concept of colligative properties using the lab, Changing Water’s Boiling Point, which guides students through an exploration using a quantitative approach. This lab activity will help students learn that adding a solute to water changes the boiling point of water and understand that the amount of solute added affects the boiling point differently. There are three versions of this lab with varying levels of inquiry. One version incorporates NGSS-based science and engineering practices.

Use the lesson, The Hot and Cold of it All to further explore the concept of colligative properties. Students analyze the effectiveness of different brands of antifreeze/coolants and their ability to protect an engine in cold climates. They then conduct a lab investigation to examine the freezing point depression in samples that have been diluted with distilled water. Additionally, students determine the specific heat capacity of different antifreeze/coolant products and explain how it relates to thermal energy transfer in the internal combustion engine. This 5-E lesson includes alignment with NGSS.

We hope that these activities can help you to reinforce several of the topics covered in a unit about aqueous solutions. 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.