BACKGROUND:
Seawater covers a little more than
70 percent of the Earth's surface. Seawater is a solution of 96.5
percent water, 2.5 percent salts, and smaller amounts of other substances,
including dissolved inorganic and organic materials and gases.
Seawater and water are similar in its chemical
and physical properties, however there are noticeable differences.
Seawater and water are both liquids and can be used to float larger substances.
However seawater is more dense that fresh water so if you mix salt and
fresh without mixing, the salt water will stay under the fresh water.
It is easier for humans to swim in salt water because the higher density
of the salt water helps to keep our bodies higher in the water. Salt
water needs more heat to boil and more cold to freeze.
PROCEDURE:
Students will compare fresh water
and salt water samples to see if they move the same on wax paper.
Salt water and fresh water are similar, but they do have different properties.
- Give each student group 2 small plastic
glasses, individual toothpicks, and wax paper. Pre mix a solution
of plain water and a solution of salt and water. Use warm water to
dissolve the salt easily.
- Go to each student group and pour one liquid in one
glass and another liquid in the other glass. Have the students
determine which glass contains the salt water and which contains the
fresh water.
- Have students determine the
difference by using their senses of taste, feel, smell and touch.
Make sure that they taste first before they put their hands in the water.
Students should easily find the salt water with taste. The fresh
water feels smoother, but this might be difficult for students to determine.
Just let them feel and smell and whatever they say is all right.
- Have the students further investigate
the properties of water by having students put two separate drops on a
piece of wax paper, about 6 inches away from each other. Tell the
students that without touching the wax paper if they can get the two drops
together. The students will experience that the water will "roll"
on the wax paper like a ball if they push it slightly with the toothpick.
This is because of surface tension which they will learn about in later
grades. Just say the word, so the students can hear it.
- Tell them to observe what they are
doing because they will then do it with the salt water. Have students
determine if the two liquids act the same. You may want to add
food coloring in the salty liquid so the students can identify that drop
easily. Do not put much, just enough to color the water.
- Once they have joined the water, you
may want to discuss how they accomplished this. After a discussion,
have the students repeat the experiment with the salt water. Ask
the students if the same thing happens? Yes. Have the students
move one drop of salt water to the fresh water. What happens?
The drops will merge, but you still can see the colored liquid separate
from the fresh water drops.
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