this post was submitted on 30 May 2025
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Whenever I leave sugar in hot water, it always form a distinct transparent layer from the water above. After I stir it, the remaining sugar will form a less distinct layer. Why don't the layers diffuse onto eachother? Can anyone explain this?

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[–] threelonmusketeers@sh.itjust.works 3 points 1 month ago (2 children)

Why don’t the layers diffuse onto eachother?

They do, you just didn't wait long enough. If the densities are different enough, sugar-water solutions can stay separated for weeks or even years. Given enough time though, they would eventually form a uniform solution.

[–] quandang@slrpnk.net 2 points 1 month ago (1 children)

How can they stay separated for so long?

[–] Impronoucabl@lemmy.world 3 points 1 month ago

For the same reason that saltwater can remain separate from fresh water, or even hot water and cold water - diffusion is typically a slow process, particularly if you do not stir, or otherwise mix the substances.

Consider this: drop a single drop of food dye into a glass of water. There's no way the entire glass immediately turns into the relevant colour, it takes time for the molecules to move about.