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Q & A: weight of solutes

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Most recent answer: 10/22/2007
does substances weigh the same after they are dissolved
- Anonymous (age 11)
Dissolving something, say sugar or salt, in a liquid, say water, has almost no effect on the weight. Certainly if you were to make a measurement of the weight with even the most sensitive lab scale, the weight of the solution would just be the sum of the weights of the liquid and the solute.

So why don't I just say that the answer is just plain yes? Relativity says that the weight is determined by the total energy of the material, including the 'rest mass' energy. When you make a solution, the material will either heat up or cool down slightly. If you let it come back to room temperature, it will have a litlle more or less energy than it started with That means it will have slightly different weight. The rest mass energy is so big compared to these other energies though that you'll never notice the change.

Mike W.

(published on 10/22/2007)

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