Why does salt water help you float?

Answer 1

Floating is the another name for the force called buoyancy and buoyancy is reliant on the density of the floater and the liquid the floater is floating in. The less dense the floater is, the more buoyant the floater will be. Salt, when added to water, makes the water more dense than the water by itself. This can be seen in an obvious way by filling a glass of water to the top and adding salt to it. It won't overflow as long as the salt is added in a form that dissolves rapidly. The volume doesn't increase, but the salt's mass is now added to the water's mass resulting in more mass for a similar volume. the formula for density is mass/volume. But that's not the whole story. The volume of water actually decreases when salt is added, so the effect on the density of the water is increased. Salt is an electrolyte. When dissolved the sodium and chlorine ions freely associate with the water. The presence of the ions causes an effect called electrostiction, which results in the water's molecular structure changing to a more compact form (bending if you will), which causes the volume to decrease. Since the density (mass/volume) of the human body (being over 60% water) is very close to the density of water, people may or may not float in water. Adding salt to the water increases the density of the water, not only through the added mass, but also by pulling the water molecules closer together. The increased density of the salt water will result in the increased buoyancy of the floater.

Answer 2

The addition of salt increases its density allowing greater buoyancy to be achieved.

For example the average salt concentration of the Dead Sea is around 31.5% which results in a density of approximately 1.24kg/L, by contrast pure water has a density of approximately 1kg/L.