A student placed equal volumes of honey and of water in two, identical, open dishes, and left them at room temperature for 8 hours. She observed that the amount of water decreased, but the amount of honey seemed unchanged. Knowing that honey is a highly concentrated solution of sugar in water, which statement should the student make to explain this phenomenon?
Answer
A
Honey has a much lower vapor pressure than pure water has. So, pure water evaporates at a much higher rate.
B
Honey has no vapor pressure. So, water evaporates at a much higher rate.
C
Honey has a much higher vapor pressure than water has. So, water evaporates at a much higher rate.
D
Honey has a much lower freezing point than water has. So, water evaporates at a much higher rate.
Explanation
Dissolved sugar lowers the vapor pressure of water in honey compared with pure water. A lower vapor pressure means fewer water molecules escape into the air, so honey evaporates more slowly. Therefore, the pure water’s amount decreases more noticeably, as stated in choice D.
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