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If you have the advantage of visiting the ocean or the
Salt Lake in Utah this summer, you may find your swimming experience in these bodies of
water to be slightly different than swimming in a freshwater lake or river. If
you accidentally get water in your mouth or eyes from the ocean or the Great
Salt Lake, you will certainly notice the saltiness of the water. But what about
floating? Is it easier to float in the ocean or Great Salt Lake than in
freshwater? And if there is a difference in your ability to float, do you think
that water from one body of water is denser than water from another body of
water? Which do you think is the most dense? Freshwater from a lake, saltwater from the
ocean, or saltwater from the Great Salt Lake? Do this experiment to find out!
test tubes (or use 3
Jar, drinking glass, or
beaker (for making the salt solutions)
Salt (you can use just regular table salt)
Red, blue, and yellow food coloring
- Measuring cup or beaker that measures in 10's of ml
What To Do
If you do visit the ocean, a freshwater lake, and/or the
Great Salt Lake, try to bring a sample of water home with you. If not, you
can make artificial ocean water and Great Salt Lake water using the
First, take the three test tubes (or jars) and label them "freshwater," "ocean
water," and "Great Salt Lake water." Set aside.
Next, make your artificial saltwater solutions to
represent the salt content of the ocean and the Great Salt Lake. The average
salinity (salt content) of the ocean is 3.5% and the average salinity of the Great Salt
Lake is 15%. You can use our recipes to make approximate saltwater solutions to
represent the salt content of ocean water and Great Salt Lake water. You may also want to heat
the water up to help the salt dissolve better, but this isn't necessary.
To approximately make ocean water, add 1/2 teaspoon of
salt to 100 ml of water, stirring well to dissolve the salt. Save some of this solution in the "ocean water" test tube.
To approximately make Great Salt Lake water, add 2
teaspoons of salt to 90 ml of water and stir. Save some of this solution in the
"Great Salt Lake water" test tube.
Fill the "freshwater" test tube with regular
Add one drop of blue food coloring to the test tube of freshwater,
one drop of yellow food coloring to the test tube of "ocean water", and one drop
of red food coloring to the test tube of "Great Salt Lake water." As each
test tube of
water receives a drop of food coloring, closely observe how the food
coloring mixes with each type of water. Can you draw any conclusions or
predictions about which type of water will be the "heaviest" based on what you
observed with the mixing of the food coloring? After making your
predictions, stir up each solution so that the color is uniform throughout
each test tube.
Fill the dropper with water from the "Great Salt Lake"
test tube, and add it to the graduated cylinder. You may need to add two or three
droppers full of water to the cylinder.
Rinse the dropper out really well with faucet water to
avoid cross contamination of salt and food coloring.
Fill the dropper with water from the "ocean"
test tube. This
time, very gently and carefully add it to the graduated cylinder so that the
force of the water being squeezed out of the dropper doesn't mix the two
waters. Add about the same amount of "ocean water" to the graduated
cylinder as there is "Great Salt Lake water." Rinse out the
dropper with faucet water.
Fill the dropper with water from the "freshwater" test
tube. Again, add the water very gently to the water already in the graduated
cylinder to avoid mixing the water, and add about the same amount of
freshwater as "ocean water."
Density is the measure of how much matter (mass) is packed into an item or
material compared to the amount of space (volume) it takes up. A material that
is more dense (e.g. lead) will weigh more than a material that is
less dense (e.g. cork) even though they both take up the same amount of space.
Or, to think of density another way, 10 pounds of cork takes up a lot more space
than 10 pounds of lead.
In this experiment, the salt added to the "ocean water" and
"Great Salt Lake water" caused these solutions to contain more matter than what
was in the freshwater even though the different types of water still took up the
same amount of space. The more salt in a solution, the more dense or "heavier"
it is, and the less salt in a solution, the the less dense or "lighter" it is.
This allows the "ocean water" to float on top of the "Great Salt Lake water"
and the freshwater to float on top of the "ocean water."
To really prove that the "Great Salt Lake water" is the most
dense, the freshwater is the least dense, and the "ocean water" has a density
somewhere in between these two types of water, try this experiment again except
this time reverse the order that the solutions were placed in the graduated
cylinder. Do they sit on top of each other as they did before or do they mix up?