Why does ice float on seawater as well as freshwater?

Why does ice float on seawater as well as freshwater?

• A. Ice is less dense than both freshwater and seawater, so it floats in both.
• B. Ice is denser than seawater but floats on freshwater due to buoyancy.
• C. Ice sinks in seawater due to salt and floats in freshwater.
• D. Ice dissolves in seawater but not in freshwater.

Answer: (A)

Buoyancy depends on density: an object will float if its average density is less than the liquid around it. Ice forms a crystal lattice that is less dense than liquid water, so it floats. Freshwater has a density of about 1.00 g/cm³, while ice is roughly 0.92 g/cm³, so ice rises to the surface. Seawater is denser because of dissolved salts, about 1.02–1.03 g/cm³, but ice is still less dense than that, so it also floats on seawater. The notion that ice sinks in saltwater or that it dissolves there isn’t correct; the key idea is that ice is consistently less dense than both kinds of water, which lets it float.

Buoyancy depends on density: an object will float if its average density is less than the liquid around it. Ice forms a crystal lattice that is less dense than liquid water, so it floats. Freshwater has a density of about 1.00 g/cm³, while ice is roughly 0.92 g/cm³, so ice rises to the surface. Seawater is denser because of dissolved salts, about 1.02–1.03 g/cm³, but ice is still less dense than that, so it also floats on seawater. The notion that ice sinks in saltwater or that it dissolves there isn’t correct; the key idea is that ice is consistently less dense than both kinds of water, which lets it float.