Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: ricbritain on 23/06/2010 23:00:21

Title: What is pure water and at what temp. does it freeze?
Post by: ricbritain on 23/06/2010 23:00:21

Tonight a friend told me that pure water does not freeze! He said that a TV show showed a beaker of pure water in a freezer unfrozen, before having a metal rod added and seeing the water immediately freeze. I presume he meant that pure water does not freeze at 0'C, as it must surely freeze at some point. So my question is, can this be true, and also what exactly constitutes pure water anyway? Is it the same as distilled water? If so I have frozen distilled water myself in a domestic freezer.

Thanks.

Title: What is pure water and at what temp. does it freeze?
Post by: lightarrow on 25/06/2010 13:21:36

1. Pure water is <<water>>.
2. Water does freeze, but in specific conditions it can freeze with more difficulty, because you can make difficult the reaching of thermodynamical equilibrium from water.
3. Putting a piece of metal, or simply giving a small stroke to the container, makes the system reach easier the th. equilibrium.

Title: What is pure water and at what temp. does it freeze?
Post by: SeanB on 25/06/2010 20:16:29

To supercool water it must cool slowly in a container that is absolutely clean, and polished so that there are no points where nucleation can occur. You place ultra pure water in it, allow it to totally still and then cool it down slowly to well below freezing. It will be most likely still liquid until you touch the surface or disturb it.

Have a quick search though Youtube for supercooled liquids.