Question

A beaker contains 100.0 mL of pure water. A second beaker contains 100.0 mL of seawater. The two beakers are left side by side on a lab bench for one week. At the end of the week, the liquid level in both beakers has decreased. However, the level has decreased more in one of the beakers than in the other. Which one and why?

Answer 1

Answer: The beaker in which water level has decreased more is the one that contains pure water.

Explanation: Even when water is not heated it can evaporate, that is because molecules move at different speed and those that are closer to surface can break the gass pressure and scape as water vapor.

The movement of molecules of water can be affected by the presence of solutes (salts or other soluble compounds) and increase the evaporation temperature. For this particular case, molecules of salt atract the water molecules (remember salt has ions and water is a dipole with partial charges) and do not let the water move freely which avoid them to scape to the surface.