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Thread: Is water the only substance that floats on itself when frozen?

  1. #1
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    Question Is water the only substance that floats on itself when frozen?

    Does frozen ammonia float on top of liquid ammonia? Or does NH3 ice sink to the bottom of the liquid NH3 its in?

    I have the same curiosity about other substances. Like methane & other hydrocarbons, peroxide, formaldehyde, as well as other chemicals.

    Water's unique, & strange, in being less dense frozen than liquid.

    I'm wondering if, & how many, other chemicals have this ability.

  2. #2
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    I'm not being much help here, but I am fairly certain I once read that water is very rare in that respect, but not unique.

    Let's hope someone a bit more informed comes along, because I'd like to know.

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    Very few, and none of the ones you mentioned. Silicon does, but it's not a liquid until you heat it to high temperatures.

    Nick

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    Quote Originally Posted by Bad Ronald View Post
    Does frozen ammonia float on top of liquid ammonia? Or does NH3 ice sink to the bottom of the liquid NH3 its in?

    I have the same curiosity about other substances. Like methane & other hydrocarbons, peroxide, formaldehyde, as well as other chemicals.

    Water's unique, & strange, in being less dense frozen than liquid.

    I'm wondering if, & how many, other chemicals have this ability.
    Look up the individual chemicals and check the liquid and solid densities. If the liquid density is higher than the solid density, then the solid floats on the liquid

  5. #5
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    Ice is less dense then water, so it floats. As far as i know it water is the only liquid that exhibits this behavior. All other liquids shrink (become more dense) when freezing instead of less dense. There are some forms of alcohol that will float when frozen on other forms of alcohol but not on same form of itself.

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    Quote Originally Posted by Bad Ronald View Post
    Does frozen ammonia float on top of liquid ammonia? Or does NH3 ice sink to the bottom of the liquid NH3 its in?

    I have the same curiosity about other substances. Like methane & other hydrocarbons, peroxide, formaldehyde, as well as other chemicals.

    Water's unique, & strange, in being less dense frozen than liquid.

    I'm wondering if, & how many, other chemicals have this ability.
    If I'm not mistaken, this property is due to water being a highly polar molecule. This means that other polar liquids should theoretically show this behavior.

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    Water is one of the most polar molecules that is still liquid at Earth-like temperatures. Its simple, small structure allows it to freeze into a consistent shape and one that is far more spacious than its liquid state.

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    Silicon has a solid density of about 2.33 g/cm3 and a liquid density at melting point of 2.57 g/cm3, so yes, the solid form floats on the melted, but that only happens around 1414 C (2577 F).

    Germanium floats too.

    Tin in it's "grey" allotropic form is lighter than the melted tin, while the "white" allotrope is heavier.


    For room temperature liquids, water is quite unique in that way.
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    Silicon, bismuth and at least one other substance I can't recall off-hand are denser when liquid than when solid. I am fairly sure water is the only one which also happens to be liquid at "room temperature".

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    Quote Originally Posted by HenrikOlsen View Post
    ... but that only happens around 1414 C (2577 F).

    For room temperature liquids, water is quite unique in that way.
    Considering that the OP mentioned liquid NH3, whether the property in question occurs at (human) room temperature or not is probably irrelevant.

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    Quote Originally Posted by Ilya View Post
    Silicon, bismuth and at least one other substance I can't recall off-hand are denser when liquid than when solid. I am fairly sure water is the only one which also happens to be liquid at "room temperature".
    Wiki:- "Other substances that expand on freezing are antimony, bismuth, gallium, germanium, silicon, acetic acid, and other compounds that form spacious crystal lattices with tetrahedral coordination."


    Funnily, apart from ascetic acid, various alloys of these elements are the basis of detectors for many types of astronomy, from radio to x-ray.

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    Bronze. It's part of why it's a popular alloy for casting...it doesn't shrink and form voids or pull away from the mold as it solidifies, and captures fine details much better.

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    Quote Originally Posted by loglo View Post
    Wiki:- "Other substances that expand on freezing are antimony, bismuth, gallium, germanium, silicon, acetic acid, and other compounds that form spacious crystal lattices with tetrahedral coordination."


    Funnily, apart from ascetic acid, various alloys of these elements are the basis of detectors for many types of astronomy, from radio to x-ray.
    Interesting, Someone should investigate the possibilities of "Vinegar Astronomy".
    Et tu BAUT? Quantum mutatus ab illo.

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    Quote Originally Posted by Ara Pacis View Post
    Interesting, Someone should investigate the possibilities of "Vinegar Astronomy".
    An especially attractive proposition for those with a sour disposition (sorry, couldn't resist).

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    Also note that in mixtures of materials, the components won't necessarily freeze out at the same time, or be in equal proportion at all times and places. As water ice freezes out of a water-ammonia mix and the ammonia concentration in the liquid portion increases, water ice will switch from floating to sinking, but may well reach more water-rich layers before reaching the bottom. Raise the temperature and shift the equilibrium toward liquid water and gaseous ammonia, and up comes the ice.

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    Question

    Frozen NH3 will sink to the bottom of liquid NH3? Likewise for CH4 & H2O2 yes?

    Makes for interesting glaciation processes on worlds where these compounds are as common & dominant as H2O is on Earth.

    Like Titan. Does CH4 {& other hydrocarbons} actually ever freeze on Titan? Or is it only in liquid & vapor forms on Titan?

  17. #17
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    Glaciation - yes, that's a point. If the solid form is less dense than the liquid, it's not going to be a case of, "Trickle into cracks in the form of rain, freee and expand, make the cracks bigger, make room for more rain."

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    Quote Originally Posted by Ara Pacis View Post
    Interesting, Someone should investigate the possibilities of "Vinegar Astronomy".
    No, all ETs broadcast on the frequency of ranch dressing.

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    Rocheworld

    If I recall correctly, there were interesting things going on with different allotropes of water ice in Robert Forward's "Rocheworld", though I could be mistaken. At any rate, a bit is mentioned about water ice in ammonia-water oceans. It's an interesting read.

    http://en.wikipedia.org/wiki/Rocheworld


    M74

  20. #20
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    Plagioclase is (sometimes) less dense in the solid form as opposed to the liquid. The lunar crust is dominated by the mineral, as the main component of anorthosite, the theory is that as plagioclase crystallised from a global magma ocean it floated to the top, forming the crust.

  21. #21
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    Ok i only thought water exhibited the light solid state. Learn something new at baut every day!

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    O2 will float on O3, temperatures work, but that may not be the same.

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