How can the content of salt be measured ?

The content of salt can be measured by building a hydrometer.

What will I need to do this?

1. Jar, 1 qt. (1 liter)
2. Modeling clay
3. Table salt
4. Measuring spoon, tablespoon (15ml)
5. Cap from a pen

How do I do this ?

Pour enough water to fill the jar three-fourths full.
Place enough clay in the pen cap to force it to sink when put in the jar of water.
Place 1 tablespoon of salt into the water and mix the solution.
Record any movements in the position of the pen cap.
Proceed to place 1 tablespoon of salt at a time until 5 tablespoons has been added to the jar.
Record any movements in the position of the pen cap.

What did you record ?

The position of the cap moved when more salt was added ?

What caused this to happen ?

The force of water pushing up on the cap is called the buoyancy force. The buoyancy force becomes greater with the weight of water. Water without salt is not as dense as salt water. As the amount of salt in the water increases, the water gets denser and has a greater buoyancy force, which lifts the cap higher in the water. The cap floating in the water behaves like a hydrometer, which is and object used to determine the salt content of water.