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I know ice floats in water because it's crystalline structure causes $H_20$ solid to be less dense than $H_20$ liquid. Is the same true for salt because it is crystalline? If not why?

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  • $\begingroup$ No: crystalinity has nothing to do with it. It's a matter of the relative density of a material in its solid and liquid phases. $\endgroup$ – Carl Witthoft Dec 18 '13 at 14:30
  • $\begingroup$ So, I think you're asking, why is ICE less dense than water? I think it has something to do with the type of bonds rather than the crystalline structure. This question may get a better audience on chemistry stack exchange? $\endgroup$ – Joe Dec 18 '13 at 14:40
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NaCl melts at around 800°C. Molten NaCl has a density of about $1.556 \frac{g}{cm^3}$[1], at room temperature (solid) it has one of $2.71\frac{g}{cm^3}$ [2]. Sadly I could not find a value for the density at barely underneath melting point but I strongly assume that the density is a strictly monotonously falling function of temperature. Therefore solid NaCl will probably sink in liquid salt. The case that Ice floats on liquid water is special and known as the anomaly of water.

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  • $\begingroup$ So crystallinity is irrelevant? $\endgroup$ – ford prefect Dec 18 '13 at 17:32
  • $\begingroup$ @fordprefect No, but it's the other way around. Generally the crystalline phase is denser than liquid. Water's crystalline phase, though, packs inefficiently. $\endgroup$ – Lenzuola Feb 6 '18 at 15:46

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