Salt Water

Summary
A lesson on why ocean water is salty. The reading is accompanied by true/false questions.

Objectives
• To explain students why ocean water is salty.

Suggested Grades
5th Grade
6th Grade
7th Grade

Excerpt
Humans need salt in their diet to achieve stable body chemistry. As Americans who frequently eat in fast food restaurants, our problem is ingesting more salt than needed rather than getting enough salt. Centuries ago salt was an important trade commodity as salt that we consume comes from mines dug into the earth. Areas with salt mines possessed a valuable natural resource that could be traded in areas lacking salt. Salt has the chemical formula NaCl, one atom of sodium combined with one atom of chlorine, and chemically is called sodium chloride. However, nature is not that simple; salt from salt mines is naturally mixed with a variety of minerals that occur in the vicinity of the mine. The food grade salt that reaches our tables is refined to remove these impurities.

Although sea salt, the salt in the ocean, is fundamentally sodium chloride, it has a different mix of minerals than salt that is mined from the earth. Sea salt also contains sulfate, magnesium, calcium, potassium, and bicarbonate and the percent of each of these components within sea salt is relatively stable across ocean water around the world. The salinity of ocean water, that is the proportion of ocean water that is accounted for by sea salt, ranges between 32 to 37 parts per thousand.

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