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Q & A: homogeneous mixtures

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Most recent answer: 01/03/2012
Q:
I read that ice cubes made from distilled water added to a bottle of distilled drinking water is a homogeneous mixture, but I thought that water is a compound, so can it technically be both? How else would the combination be classified?
- Tara (age 42)
NY, NY, USA
A:
We often get these sorts of vocabulary questions. Please pardon the following philosophical rant, which is not directed against you or your perfectly reasonable question but rather against an educational system that puts far too much emphasis on vocabulary at the expense of substantive content.

You know what the situation is: you have some frozen water floating around in some unfrozen water. Almost all the molecules are H2O. A few temporarily fall apart into H+ and OH-. From these sorts of physical  facts you can figure out the mass density, the chemical reactivity, the vapor pressure, the electrical conductivity, and so forth for all the measurable properties.

What this doesn't tell you is what names to use. Beats me. If the names told us something extra about the way the material behaved then we'd have to figure out which name was right. If I had to choose, I'd say that so long as there are separate chunks of ice it doesn't make much sense to call the material "homogeneous".

Mike W.



(published on 01/03/2012)

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