What is the difference between evaporation from a pure liquid and evaporation from a solution?

What is the difference between evaporation from a pure liquid and evaporation from a solution?

• A. Evaporation from a pure liquid concentrates solute.
• B. Evaporation from pure liquid freezes the liquid.
• C. Evaporation rates are the same.
• D. Evaporation from a solution concentrates the solute.

Answer: (D)

When a liquid evaporates, molecules escape into the gas phase. In a pure liquid there’s no dissolved substance, so as some liquid leaves, the remaining liquid simply gets smaller but stays the same pure substance. In a solution, there is a dissolved solute that doesn’t readily evaporate with the solvent. As the solvent evaporates, the amount of solute stays the same while the solvent amount decreases, causing the concentration of solute in the liquid that remains to rise. So evaporation from a solution makes the solution more concentrated (and can lead to crystallization if it becomes saturated).

When a liquid evaporates, molecules escape into the gas phase. In a pure liquid there’s no dissolved substance, so as some liquid leaves, the remaining liquid simply gets smaller but stays the same pure substance. In a solution, there is a dissolved solute that doesn’t readily evaporate with the solvent. As the solvent evaporates, the amount of solute stays the same while the solvent amount decreases, causing the concentration of solute in the liquid that remains to rise. So evaporation from a solution makes the solution more concentrated (and can lead to crystallization if it becomes saturated).