Solubility of an Ionic Compound (NaCl) Model

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This model is designed to show how ionic compounds like sodium chloride dissolve in water. The sodium (orange) ions and chlorine (green) ions, along with water molecules, are all accurately sized. The bulk crystal is face-centered cubic. Separate ions can be printed and placed on top of the molecule in the same repeating structure. Using the included water molecules, the process of dissolving an ionic compound can be shown by removing individual ions. Files are available to print the model on dual extruder printers (recommended) and single extruder printers. For a single extruder, the individual ions that are placed on top of the model can still be printed in separate colors. **Some sodium ions on the edge of the crystal may fall off when supports are removed from the model. (Moving them farther into chlorine just looks weird).** Print Settings Printer: Flash Forge Creator Pro Rafts: Yes Supports: Yes Resolution: 0.2mm or higher Infill: 15% Standards NGSS CCSS Overview and Background Often, students struggle to grasp the concept of solubility on a particle level. This model can be used to demonstrate how an ionic compound separates into ions when dissolved. The model can also be used to show the structure of ionic crystals. Students should be familiar with the differences between ionic and molecular compounds before using this model. Objectives: Students will be able to describe the process by which an ionic compound dissolves in water. Students should be able to explain how water molecules interact with ionic compounds through intermolecular forces Students should be able to explain why certain substances can form crystal structures. Lesson Plan and Activity Show students some table salt and ask what will occur when the compound is dropped into water. Discuss what occurs on a macro level (it dissolves) and then ask students to draw what they think will happen on a particle level. Show the model of sodium chloride already set up with one or more layers of individual ion pieces on top. Pour some water onto the model (by dropping the included water molecules onto the model and knocking the individual ions off the crystal). This can lead to discussions about how water molecules interact with positive and negative ions through ion-dipole forces, why the ions break apart, and about how the surface of the crystal must dissolve before the interior. Materials Needed No other materials are needed besides the model kit, although a document camera may be helpful in demonstrating how the model works.