Printer Friendly

Practices of Science: Making Simulated Seawater

NGSS Science and Engineering Practices:

<p><strong>SF Fig. 2.2 </strong>Measuring salt to make simulated seawater</p><p><strong>SF Fig. 2.3.</strong> The average ocean surface salinity from August 25 to September 11, 2011, produced by the National Aeronautics and Space Administration (NASA) science satellite Aquarius. Red indicates areas of high salinity. Purple indicates areas of low salinity.</p><br />


Scientists use models or simulations in many situations. Models are often used because it is difficult to obtain or work with the real thing that scientists want to study. Many activities in Exploring Our Fluid Earth use simulated seawater, which you will see called “salt water” in the activities. Simulated seawater is easy to make and can be standardized (SF Fig. 2.2), unlike real ocean seawater, which may be difficult to collect and may vary in salinity (SF Fig. 2.3). Salinity can be expressed in units of parts per thousand, ppt, which is equivalent to how many grams of salt are in 1,000 grams (g) of water.

 

How to make water for different conditions:

Fresh water—less than 0.5 parts per thousand (ppt)
Fresh water contains trace amounts of salt and other dissolved substances at very low concentrations. Tap water can be used to simulate fresh water.

 

Brackish water—20 ppt
Brackish water is less salty than seawater, but it is more salty than fresh water. Brackish water can be found where fresh water mixes with seawater, for example in estuaries and where rivers flow into the ocean. Brackish water contains between 0.5 and 30ppt of dissolved salt.

  1. Weigh 20 grams (g) of salt.
  2. Add the salt to a beaker and add fresh water until the total mass is 1,000 g.
  3. Stir with a stirring rod until all the salt is dissolved.

 

Salt water—35 ppt
Seawater ranges in salinity from 33 to 38 ppt (SF Fig. 2.3). The average salinity of ocean water is 35 ppt.

  1. Weigh 35 g of salt.
  2. Add the salt to a beaker and add fresh water until the total mass is 1,000 g.
  3. Stir with a stirring rod until all the salt is dissolved.

 

Hypersaline water—50 ppt
Hypersaline water is water that is saltier than seawater. Hypersaline water can be found in some lakes, as well as in tidepools separated from the ocean where some water has evaporated, leaving behind saltier water.

  1. Weigh 50 g of salt.
  2. Add the salt to a beaker and add fresh water until the total mass is 1,000 g.
  3. Stir with a stirring rod until all the salt is dissolved.

 

What type of salt should be used in making simulated seawater?

There are many different kinds of salt that can be used to make simulated seawater, such as table salt, kosher salt, sea salt, and rock salt. Kosher salt will result in the least cloudy salt water, but any type of salt solution will decrease in cloudiness if left to sit for a few hours or, better yet, overnight.

 

Although the salts listed above will work in experiments that call for using salt water or seawater, none of these salts are appropriate for making saltwater aquaria. This is because, although seawater is primarily a solution of sodium chloride (NaCl) in water, there are several other dissolved chemical compounds in seawater that are important for living organisms. Because table salt does not contain these additional dissolved substances, it cannot be used to create a saltwater aquarium. Sea salt does contain additional minerals, but the concentrations of these are not standardized, so it is not a good choice to use in a saltwater aquarium. Commercial sea salt formulated for aquariums and sold at pet supply stores contains trace elements in concentrations consistent with natural seawater and therefore can be used in saltwater aquaria.

Special Feature Type:

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.