Learning Lesson: Salt 'n Lighter

Overview

Just as air can have different densities, water can have different densities as well. As the salinity of water increases, the density increases as well. Fresh eggs will float in salt water, but will sink in fresh water. This will show that as the salinity increases the density also increases.

Procedure

1. Fill each beaker with one liter of tap water (or each quart jar with one pint of water).
2. Add 35 grams of salt to one beaker and 290 grams of salt to a second beaker (½ ounce of salt to one-quart jar and 4½ ounces of salt to a second jar).
3. Ask the students to speculate in which water solution, if any, will the eggs float.
4. Place an egg in each solution and observed which egg floats.

Discussion

Fresh eggs are more dense than fresh water and therefore will sink. However, as the water's salt content increases, it becomes denser. The eggs float in the two beakers with the added salt.

The solution with the 35 grams of salt represents the salinity of the oceans. The solution with 290 grams of salt added represents the salinity of the Dead Sea. The egg in the beaker with the most salt should float higher than the egg in the less salty solution.

The increased density of salty water increases the weight of water. An egg will be buoyant (float) if the weight of the egg is less than the weight of the water it displaces. The egg sinks if it weighs more than the weight of the water that is displaced.

Ships float for the same reason. The physical weight of the ship is less than the weight of the water that is displaced. Since the weight of the water displaced is greater, ships float.