| MadSci Network: Chemistry |
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When the dishwasher finishes its cycle, the glasses and ceramic plates are
dry, but plastics such as Tupperware have water drops on their surfaces.
Why?
This is a very good question, and I think the answer is probably a simple one. Dishes in the dishwasher are typically dried by heating them to drive off the water. But water has a high heat capacity, and it takes a lot of energy to evaporate it completely. Most dishwashers nowadays are designed to use as little energy as possible, so they are probably designed to take advantage of the fact that most items either heat quickly (metals are excellent conductors of heat) or store heat for a time (glass and ceramics have high heat capacities). Unfortunately plastic neither heats quickly, like a metal, nor stores heat, like glass and ceramic. So it dries best by gravity (as in a draining rack) and doesn't come out of the dishwasher cycle dry.
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