What happens to a solution when the solvent evaporates?

• A. The solute evaporates, leaving solvent behind and decreasing concentration.
• B. Both solvent and solute evaporate, keeping the concentration the same.
• C. The solution freezes.
• D. The solvent evaporates leaving dissolved solutes behind, increasing the solution's concentration.

Answer: (D)

When the solvent evaporates, the amount of solute in the solution stays the same while the solvent volume decreases. Since concentration is the amount of solute per unit volume, removing solvent makes that ratio larger, so the solution becomes more concentrated. The dissolved particles remain in the liquid (until saturation is reached and precipitation or crystallization can occur). This is why the correct description is that the solvent evaporates, leaving behind the dissolved solutes and increasing the solution’s concentration.