Dissolving

Interactive, scaffolded model

Overview and Learning Objectives

In this activity, students determine what holds ions in solution, and they experiment with dissolving different solutes in various solvents.

Students will be able to:

• explain on the microscopic level that the process of dissolving is the result of interactions between water molecules, between particles of the substance being dissolved, and the interactions among those particles and water;
• reason that, for dissolving to occur, the interactions between molecules of the substances with water molecules must be stronger than their attractions to each other.

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Classroom Practice

The Dissolving model-based activity is designed to help students learn what is happening at the atomic level when a substance dissolves. Students see that particles of the substance, such as ions or polar molecules, are attracted to water molecules more strongly than they are attracted to each other. It is these intermolecular attractions that are responsible for the process of dissolving.

In this activity students will consider what happens when different types of substance are added to water:

• ionic compounds such as sodium chloride;
• polar ogranic substances such as sugar;
• lipids, partially charged organic molecules consisting of long non-polar chains at one end and a charged group of atoms on another;
• completely neutral non-polar substances such as parafin or fat.

For this activity to be most successful, students should have some idea about the different types of bonds (Stepping Stone 2) as well as understand that the strong polar nature of water molecule allows it to be one of the most universal solvents.

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Central Concepts

Key Concept:

Polar water attracts polar molecules and ions, and pushes out non-polar and non-charged substances.

Additional Related Concepts

Concept Map Available

Physics/Chemistry

• Dissolving
• Salt
• Solubility
• Solutions

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Textbook References

• Biology: Exploring Life - Chapter 4: The Chemical Basis of Life
• Biology: The Dynamics of Life - Chapter 6: The Chemistry of Life
• BSCS Blue (8th Edition) - Chapter 1: The Chemistry of Life
• BSCS Human - Chapter 5: Maintaining Balance in Organisms
• Web of Life - Chapter 2: Chemical Basis of Life
• Web of Life - Chapter 30: Digestive and Excretory Systems

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Benchmarks and Standards

AAAS

• THE PHYSICAL SETTING: FORCES OF NATURE - There are two kinds of charges-positive and negative. (Full Text of Standard)
  
  

NSES

• Life-Science: Matter, energy, and organization - 1 All matter tends toward more disorganized states (Full Text of Standard)
  
  
• Physical-Science: Matter Structure/Properties - 4 The physical properties of compounds reflect the nature of the interactions (Full Text of Standard)
  
  

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Extensions and Connections

There are several models in the database that help students learn about water. If your students have not acquired this information, you may want to have students do these models first:

The model Water: Getting to Know the Water Molecule -- Activity #140 (http://molo.concord.org/database/activities/140.html) has students look at the properties of water and how these properties influence intermolecular interactions.

This dissolving activity was originally field tested as part of a unit on solutions and solubility, Aquatic Solutions and Our Cells

(http://workbench.concord.org/web_content/unitIII_mini/index.html).

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Activity Credits

Created by CC Project: Molecular Workbench using Molecular Workbench + Pedagogica

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Requirements

• Java 1.5+ - Java 1.5+ is available for Windows, Linux, and Mac OS X 10.4 and greater. If you are using Mac OS X 10.3, you can download MW Version 1.3 and explore within it instead.

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