Grade 2 students learn to measure salinity - and how to survive on a desert island!

Concordia Grade 2 students made designs to help them survive on a deserted island as part of their Physical Science Unit. 

The classes visited Mr. Stapley in the High School science labs to build their own rudimentary salinometers – a tool for measuring the saltiness of water – and use them to determine which “water source” would be acceptable for drinking. 

First, students learned about the concept of density, and how salty water has a different density than freshwater. Students then built simple salinometers out of straws and clay and calibrated them using drinking water. 

To do this, students stuck the ball of clay to the bottom of the straw and dropped it into drinking water to see if it would float. If it did not, they adjusted the amount of clay attached to the straw until the straw and ball creation would float and stay upright in the water. Students marked on the straw with a permanent marker at the spot where the straw touched the water line. 

“It was exciting…I didn’t know that it would float,” said Chaelin. 
“How did the straw float with a lot of clay on it?” said YoonSeo. 

Once their salinometer was calibrated, they were ready to test water samples to determine which one had high salt content and which one was fit for drinking. Students dropped their salinometers into each sample. The sample where their test line met the water was the potable water and the sample where the line was above the water indicated the overly salty water. In this way, the students were able to say if they would want to bring the red or blue water with them and discuss how they knew which water would be best to fill the container for their boat. 

“First I thought that the salt water was red, but I figured out that it was blue because it floats up higher and in the red it floats lower,” said Lina.
“I didn’t know that there is air inside the straw,” said Minh.  

The salinometers were easy to make and use, but a powerful tool to help students understand the properties of the water they were testing - and teach students to think about what was happening around them in a new way. 

Learn more about Concordia’s Elementary School program.