Rock Cycle - Chemistry (4)
Post Lab 

   
OBJECTIVES:
  • Exploring the historical significance of salt.
  • Searching for information on salt.
VOCABULARY:
  • compound
  • element
  • halite
  • mineral
  • salt
MATERIALS:
  • The Salt Institute Video
  • Internet

Students learn about the historical significance of salt.


Solar salt and its red color caused by salt loving bacteria

BACKGROUND:

Salt is an important resource in the United States and other nations. It is used every day in many aspects of our lives, from manufacturing to water purification. It is also an essential ingredient for maintaining a fluid balance in our bodies.

Salt crystallizes in a cubic pattern, and usually has a cubic appearance in hand specimens. The melting point of salt is 800E C. It dissolves easily in cold water and a little more readily in hot water. Common salt, when mixed with ice, lowers the melting point of the ice, making it melt. Salt is thus used on ice covered streets, so people or cars will not slip.

Common salt is also used in many manufacturing processes. It is employed as a preservative or seasoning in food processing, for curing hides, and as a brine for refrigeration. It is used to make sodium carbonate (washing soda), sodium bicarbonate (baking soda), sodium hydroxide (caustic soda), hydrochloric acid, bleaching powder, and many other chemicals. It is also used as a flux in metallurgical processes. It is also an important ingredient in the manufacture of cement.

Salt, often said to be worth its weight in gold, has played a vital role in nearly every civilization since the beginning of time. It has served to preserve and improve the taste of food, as money, and as a spiritual icon. Some examples are listed below:

  • Ancient Greeks exchanged their slaves for salt
  • Romans paid their soldiers partly in salt
  • Chinese, in 2700 BC, wrote of 40 different kinds of salt
  • The French Revolution was sparked, in part, by a salt tax
  • Ancient Ethiopians used salt disks as a form of currency
  • In the United States, the Erie Canal was built largely to transport salt
  • In Slavic countries, salt is given to a bride and groom to symbolize health and happiness
  • Many of Napoleon's troops died during retreat from Moscow due to a lack of salt
  • The English increased their use of salt during Queen Elizabeth's reign when she required her subjects to eat fish on Wednesday and Friday
PROCEDURE:
  1. Show the Salt Institute video (can be purchased from The Salt Institute website listed below). This presentation shows that salt is essential for life. It will take students to far away places and trace the historical importance of salt. It explores the collection and packaging of salt, as well as its various forms and uses throughout the United States, (including the "mining" and harvesting technology used in the San Francisco Bay area.)
      
  2. Have the students write a paragraph on the importance of salt. They can find information in the library or search the internet. You may want to start with The Salt Institute web site which is full of historical information (http://www.saltinstitute.org

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