Water Salinity and Density

Salt water and fresh water can form distinct layers due to differences in density. By testing with an egg and layering colored water, students can observe how salinity affects whether water sinks, floats, or mixes.

1. Fill a jar with fresh water and place an egg inside. Observe how it sinks.
2. Add spoonfuls of salt to the jar, stirring until dissolved. Keep adding until the egg floats, showing that the salt water is denser than the egg.
3. Fill two additional jars with fresh water. Add one food coloring to the first jar and a different color to the second.
4. Stir salt into the first jar to make salt water. Place it on a tray.
5. Cover the second jar (fresh water) with a plastic board, flip it over, and carefully align it on top of the salt water jar. Remove the board so the jars touch. Observe how the fresh water stays on top and the two layers remain separate.
6. Repeat the setup, but this time place the salt water on top. Notice how it sinks quickly and mixes with the fresh water.

Water Density Experiment | Why Salt Water and Fresh Water Don't Mix - Hungry SciANNtist:

Water salinity and density experiment | At Home Science Experiment - Scitech WA:

📄 Water salinity and density - Scitech: https://www.scitech.org.au/experiment/water-salinity-density/

• Try using different amounts of salt to test how salinity levels affect density.
• Replace the egg with other objects (grape, coin, plastic bead) to see if they float in different water densities.
• Use warm and cold water instead of salty and fresh to explore temperature effects on density.

• Handle jars carefully to avoid spills or breakage.
• Do not drink or taste the salty water.
• Clean up food coloring spills promptly, as they may stain surfaces.

• Why does the egg sink in fresh water but float in salt water? (Because salt increases the density of the water until it is greater than the egg’s density.)
• Why do fresh and salt water form layers instead of mixing? (Because the density difference prevents mixing until external forces like stirring or waves disturb them.)
• What happens when salt water is placed on top of fresh water? (It sinks and mixes, because it is denser.)
• How does this experiment relate to real rivers and oceans? (It models haloclines, where fresh river water flows over salty ocean water.)