As the solvent evaporates from a solution, what happens to the solute concentration?

• A. Remains unchanged
• B. Concentration decreases
• C. Concentration increases
• D. Solute precipitates

Answer: (C)

When a solvent evaporates, the amount of solute stays the same while the solution’s volume decreases. Concentration is the amount of solute per unit volume, so with less solvent and the same solute, that ratio goes up. So the solute concentration increases as evaporation continues. If the solution becomes saturated, some solute might start to precipitate, but the immediate effect of evaporation is an increasing concentration.