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Dissolving Salt in Water (SAS)

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Dissolving Salt in Water (SAS)

Grade Levels

10th Grade, 11th Grade, 12th Grade, 9th Grade

Course, Subject

Chemistry, Science
Related Academic Standards
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Description

This activity allows you to investigate how salt dissolves in water.  Students will first look at the chemical structure of salt. Students will be able to describe why a crystal of salt formed as the water evaporated from a drop of salt solution.

Water moves, carrying particles of different sizes in solution. The most common substance that dissolves in water is probably salt. Oceans, which cover nearly 70% of Earth’s surface, are salt-water solutions.

Death Valley, California, pictured above, contains salt pans. During the middle of the Pleistocene era there was a succession of inland seas located where Death Valley is today. As the area turned to desert the water evaporated, leaving behind the abundance of salts such as common sodium salts and borax.

Thanks to intermolecular attractions, the crystal structure of salt is very stable. Salt does not melt at room temperature nor does it evaporate into the air. But when it is in contact with water, something dramatic happens.

Salt is an ionic crystal consisting of positive sodium ions (Na+) and negative chloride ions (Cl-) strongly bound together, which form a lattice as shown in the models. The models are simplified two-dimensional ones. In reality, salt’s structure is three-dimensional. The 2D model is a layer of the 3D structure.

Some of the following models show a microscopic view of what happens at the salt-water interface. The red atoms represent oxygen and the white ones hydrogen of the water molecules.

Rationale

Is dissolving salt in water a chemical reaction?

Resource

CLICK ON THE PICTURE BELOW TO PROCEED TO THE ACTIVITY

Content Provider

The Concord Consortium: http://www.concord.org/

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