Which beaker shows a greater decrease in liquid level after being left side by side on a lab bench for 1 week, a beaker with 100.0 mL of pure water or a beaker with 100.0 mL of seawater, and why?

Verified step by step guidance

1. Identify the key difference between pure water and seawater: Pure water is composed solely of H2O molecules, while seawater contains dissolved salts and other substances.
2. Understand the concept of evaporation: Evaporation is the process where liquid molecules escape into the gas phase. It occurs more readily in pure substances due to fewer intermolecular forces compared to solutions.
3. Consider the effect of dissolved salts in seawater: The presence of salts in seawater increases the boiling point and decreases the vapor pressure compared to pure water, which means seawater evaporates more slowly.
4. Compare the evaporation rates: Since pure water has a higher vapor pressure than seawater, it will evaporate more quickly under the same conditions.
5. Conclude which beaker shows a greater decrease: The beaker with pure water will show a greater decrease in liquid level after one week due to its higher evaporation rate.

Key Concepts

Evaporation

Evaporation is the process by which molecules at the surface of a liquid gain enough energy to enter the gas phase. It occurs at any temperature and is influenced by factors such as temperature, surface area, and humidity. In this context, both beakers will experience evaporation, but the rate may differ due to the composition of the liquids.

Colligative Properties

Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute. Seawater contains dissolved salts, which lower the vapor pressure of the solution compared to pure water. This means that seawater will evaporate more slowly than pure water, leading to a smaller decrease in liquid level.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase. Pure water has a higher vapor pressure than seawater due to the absence of solutes. As a result, the beaker with pure water will show a greater decrease in liquid level over time, as it evaporates more readily than the seawater, which has a lower vapor pressure due to the presence of dissolved salts.