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Education: Activities & Documents

Salt crystals magnified by 100
The Nature of Salt
Chemically, table salt consists of two elements, sodium (Na) and chloride (Cl). Neither element occurs separately and free in nature, but are found bound together as the compound sodium chloride. It occurs naturally in many parts of the world as the mineral halite and as mixed evaporites in salt lakes. Seawater contains an average of 2.6% (by weight) sodium chloride, or 78 million metric tons per cubic kilometer, an inexhaustible supply. Table salt, when viewed with a magnifying glass, can be seen to consist of tiny, cube-shaped flakes. The microscope image seen at the right shows table salt crystals magnified by 100. - From The Salt Institute.

Did you ever wonder why the oceans are filled with salt water instead of fresh? Just where did salt come from? And is it the same salt you find on a dining room table? Most of the salt in the oceans came from land. Over millions of years, rain, rivers, and streams have washed over rocks containing the compound sodium chloride (NaCl), and carried it into the sea. Some of the salt in the oceans comes from undersea volcanoes and hydrothermal vents. When water evaporates from the surface of the ocean, the salt is left behind. - From the Office of Naval Research.
  • Big Idea. Sodium chloride or common salt is the chemical compound NaCl, composed of the elements sodium and chlorine. Salt occurs naturally in many parts of the world as the mineral halite. Seawater has lots of salt; it contains an average of 2.6% (by weight) NaCl, or 78 million metric tons per cubic kilometer.
  • Grade Level. High School.
  • Time One 45 min. period.
  • Content Standard. NSES Physical Science, structure & properties of matter: Bonds are created when electrons are transferred or shared among elements. Atoms or ions may bind together to form molecules or crystalline solids (e.g., salts).
  • Ocean Literacy Principle. (1e) Most of Earth's water (97%) is in the ocean. Seawater has unique properties: it is saline, its freezing point is slightly lower than fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic.
Periodic Table; chemistry reference book or web access (optional); spheres of styrofoam, clay, etc. (some spheres should be about twice the size of others); student worksheet; toothpicks, straws, etc.