Why Does Ice Float

  woodchip 14:46 24 Mar 2013

Water reaches its maximum density at 4°C (40°F). As it cools further and freezes into ice, it actually becomes less dense. On the other hand, most substances are most dense in their solid (frozen) state than in their liquid state. Water is different because of hydrogen bonding. So how did that come about. as it lets fish and other living thing survive under it

  Chronos the 2nd 14:51 24 Mar 2013

A water molecule is made from one oxygen atom and two hydrogen atoms, strongly joined to each other with covalent bonds. Water molecules are also attracted to each other by weaker chemical bonds (hydrogen bonds) between the positively-charged hydrogen atoms and the negatively-charged oxygen atoms of neighbouring water molecules. As water cools below 4°C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This produces a crystal lattice, which is commonly known as 'ice'.

Ice floats because it is about 9% less dense than liquid water. In other words, ice takes up about 9% more space than water, so a litre of ice weighs less than a litre water. The heavier water displaces the lighter ice, so ice floats to the top. One consequence of this is that lakes and rivers freeze from top to bottom, allowing fish to survive even when the surface of a lake has frozen over. If ice sank, the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze solid.

  rickf 14:58 24 Mar 2013

And to follow it results in the density of ice being lower than that of water.Stand corrected if I am not. But I seem to remember this from my Science lectures when doing my 'O' Levels many many years ago.

  john bunyan 14:58 24 Mar 2013

Water molecules have two hydrogen and one oxygen atoms. The oxygen atom attracts the negative charge from the hydrogen ones in the liquid state. As it freezes the negative charge pushes the atoms in the moecule apart so the frozen molecules are less dense than the liquid one, so ice floats.

  lotvic 15:09 24 Mar 2013

So if you add some antifreeze to the water, how does the antifreeze work to alter things?

  john bunyan 15:21 24 Mar 2013

Ethylene glycol has a freezing point of -40 deg C so depending of dilution level in water it reduces the mixture's freezing point.

  Forum Editor 16:21 24 Mar 2013

Chronos the 2nd's response - pasted from this source provides the correct answer.

If you're going to paste more than a few lines of copyright protected material from another website into a forum post it's good practice to acknowledge the source - either with a typed attribution or a direct link to the original text.

  wee eddie 16:26 24 Mar 2013

Lucky for us that it does float.

If it sank, life, as we know it, would not exist on this planet.

And the 4'C anomaly helps us as well!

  Chronos the 2nd 16:27 24 Mar 2013


  bumpkin 16:48 24 Mar 2013

Lighter than water

  lotvic 16:56 24 Mar 2013

4'C anomaly - is that the one where it sinks to the bottom?

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