Oceans

Why is the ocean salty? How much of the world's surface is ocean?

Objectives:

Students use writing, reading to record change over time. Students write explanations of how salt changes in water. Students relate learning to prior knowledge verbally and in writing.

Materials:

Two small clear plastic cups for each student (reuse the first cup for the second lesson)

Two large clear plastic cups.

Permanent marker

1 lb. Rock salt

Table salt

Spoons

A baking sheet or tray to catch spilling during dissolution races.

Procedure:

a. Each student writes their name on a clear plastic cup. Fill with water and a teaspoon of rock salt (materials managers etc.). Students write as many descriptions and adjectives as they can think of to describe how the salt appears in the cups. Students can taste the water a little to describe if the water doesn't taste salty, is a little salty or is very salty.

Store the cups together out of heat or sunlight. Cover them to keep dust out.

A few days later, pass out the same cups and the salt will be easy to dissolve. Students will review what they wrote and write more to record what changed. How does the water taste now? (No one can drink it of course!)

b. Show the class two large clear plastic cups of water. Place a tsp. of rock salt in one cup. Place a tsp. of salt (like from the table) in the other. Ask the students to write predictions of which can be dissolved faster. Two students have a race to dissolve the different salt in the cups. Repeat the race a few times to confirm the results. Have students reread their predictions and write some simple sentences describing what actually happened. What was the only difference between the two cups of salty water?

c. The ocean is salty because water dissolves salt (found as a mineral) in rocks underwater. How are our cups like the ocean? How much did the salinity change?

d. How much fresh water is there to drink?

Give each student two cups. (one cup with their name from before)
Fill one cup with water and leave the other empty on their desks. Students hold the water with both hands.
Tell students, " We're going to pretend your cup has all the water in the whole world". Have a world map posted that can point out the following.
Students spill one drop into the empty cup. No more than one drop. This represents all the water in river and lakes.
Students spill one more drop. This represents all the water underground.
Students spill one more drop for all the water in the air.
Students spill two more drops. This is all the ice in the world.

Now put down the full cup. Students can drink the few drops of spilled water but that's all there is. The 'full' cup represents salt water in the cup of all the water in the whole world. Less than 3% of the world's water is fresh.

Distribution of the world's water

Oceans 97%

All icecaps/glaciers 2.0%

Groundwater .62%

Freshwater Lakes .009%

Inland seas/ salt lakes .008%

Atmosphere .001%

All rivers .0001%

Total 99.8381

Source: The Cousteau Almanac. New York:Doubleday/Dolphin.1981 Page 114.

Close:

List all the ways we use water. List all the places we find water. Relate water to other prior knowledge. Write a story about rain, oceans, storms or snow. Read about people who sail across oceans. Write a journal entry about crashing in a hot air balloon.

Our Class | Centers | Books |

Links for KIDS! | Home