Water Densities in the Great Salt Lake

(4th grade, 50 minutes)

Objective:

To learn about different densities of water in the lake and how they affect the flow of water in it.

Materials:

• A fish tank with paper taped behind it
• Four pitchers
• Three colors of food coloring
• Enough salt for three pitchers of salt water
• Enough ice for one pitcher of ice water
• Fine soil to make a pitcher of muddy water

Vocabulary & Discussion (20 minutes):

‘Density’

A bottle of water weighs more than a bottle of air.

How can you make water more dense?

Add dirt, salt, etc.

How can you make water less dense?

Mix in air bubbles.

What else can change density? Hint—It would make the density change with the seasons.

Temperature.

(They may not know the term ‘molecule’ yet.)

‘Buoyancy’

A stick is more buoyant than a rock.

It is tied to density.

Because the Great Salt Lake is more dense than normal freshwater lakes, you would float higher in the GSL.

‘Turbidity’

Turbid water has dirt in it.

‘Terminal Lake’

‘Salinity’

Salinity of the Great Salt Lake continues to increase because water evaporates, but the salt stays there. The GSL is 3-5 times saltier than the ocean.

‘Density Current’

Railroad causeway cuts GSL into North and South sides—North side is much saltier because it doesn’t have a lot of rivers flowing into it. This causes density currents in the tunnels under the causeway.

Procedure (30 minutes):

• Make four pitchers of water mixtures and put a different color of food coloring in each non-muddy pitcher.
  1. Lukewarm and somewhat salty
  2. Lukewarm and very salty
  3. Iced and very salty
  4. Muddy
• Fill the fish tank part way full of lukewarm water. Position it with one end higher than the other so that the water is very shallow at the higher end (See picture above). Also, the paper should be on the background side of the tank.
• Slowly pour each type of colored water, in the order indicated by the numbering above, into the tank at the shallow end and allow it to settle into a colored layer. Before each one, describe to the students what you are about to do and ask them to predict what will happen. Then see if their predictions were correct. Discuss how each liquid goes to the bottom because it is even more dense than the last one.