Salinity

What do ocean water, the Dead Sea and the Great Salt Lake have in common?  They are all very salty!  Many types of salts are dissolved in natural waters. As they dissolve, the attractions that hold charged atoms together come apart, and the separated and charged atoms are called ions. The most abundant ions in the sea are chloride (Cl-) and sodium (Na+), which together form table salt, or Sodium Chloride. These ions account for 85% of all ions in water.
 
What happens to salt when water was evaporates? Yes, it gets left behind.  Both the Red Sea and the Mediterranean have a lot of evaporation, and a great deal of salt gets left behind in the process. But it gets tricky – if they had better mixing with the rest of the ocean, the salt level, which we call salinity, would be lower.
 
Salinity is a measure of the concentration of total salts (in grams) dissolved in the water. Salinity is usually expressed in parts per thousand (ppt). This means that for every 1 liter (1,000 mL) of water, there are 35 grams (or "parts") of dissolved salts.
 
For example, ocean water salinity is normally about 35 ppt.
Freshwater, on the other hand, tends to have very low levels of salinity, usually less than 1 ppt.
 
Brackish water, where fresh water meets salt water in areas like a tidal area, salinity is between 1–10 ppt.
 
But the Dead Sea has about 225 PPT!
 
How much salt is in our own water and sand? Here is a report from your Global Lab colleagues in Hawaii.

Hawaii Global Lab Students Experiment with Salts

"For the salt content experiment, we wanted to do testing by evaporating different amounts of beach/bay water so as to get a better idea of how much salt was in the water.  But, unfortunately, due to [lack of] time, we were unable to do as much as we wished.  But we did evaporate two different amounts of beach/bay water [25 mL, 100 mL).  It took time and patience to wait and watch the water boil and then evaporate.

We had a hard time controlling the amount because it splattered.  As a result, salt was lost, altering the data. This was one of the factors affecting the results.

Another was the sand and other objects in the water.  Sand couldn't be burned off so it was left with the salt adding weight. Thinking about it now, we concluded that the next time we should filter the sand [out] before we burn it.

Another thing that affected the results was the weight of the beach/bay water.  In the 100 mL experiment, the weight of the water varied greatly --74.3, 73.1 and 76.5.  This surely caused the amount of salt to vary.  After looking over the results, we concluded that Ala Moana and Kaneohe Bay have almost the same amount of salt.  Kailua Bay has the least.

Use of salts by animals. Of course there are other types of ions in the oceans including sulfate (SO42-), magnesium (Mg2+), calcium (Ca2-), and potassium (K+). Some of these ions are taken in by organisms living in the water, thereby lowering the concentrations dissolved in the water. For example,many organisms remove calcium ions from the water to form their shells and skeletons.  Sodium and Chloride Ions are not used very much by aquatic animals, and are found in higher concentrations." - Consuelo Rogers, Honolulu and her chemistry class

Use a hydrometer to measure the salinity of your water samples!

Look at a model of salt dissolving

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