I have a 1 inch long, 1/2 inch thick sponge. For my experiment, the sponge must
ID: 7118 • Letter: I
Question
I have a 1 inch long, 1/2 inch thick sponge. For my experiment, the sponge must be submerged in a liquid for 20 hours. During these hours, I can do anything I wish (using any materials) to keep the sponge from evaporating water. After these 20 hours are done, the sponge must sit out in the open for 4 hours. During these hours I cannot disturb the sponge in any way. When these 4 hours are up, my sponge must weigh more than it did before it was submerged. My question is: How can I keep the sponge from evaporating water while it is out in the open for 4 hours?Explanation / Answer
A thin layer of oil on top of water will mostly prevent the water from evaporating, because the oil will float on top of the water and keep the water molecules from escaping from the water's surface. Water dissolves very little in ordinary oil, so hardly any water molecules diffuse through the oil. Some oils evaporate themselves, though, and if you wait long enough, the oil may evaporate away, leaving a hole for the water underneath to evaporate. If the oil layer is too thin, it may leave a hole somewhere for the water molecules to escape by evaporation. Emulsifying agents, like soap, stick to oil molecules and to water molecules, allowing the two to mix. Adding soap to water with oil on top of it may allow the water to evaporate. Really dirty oil, like the stuff you get out of car engines if the oil isn't changed often enough, may contain so many small metal particles in it that it will sink in water. This kind of oil will just sit on the bottom and not affect the evaporation rate.
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