Instant Ice

By Linda | November 22, 2008

Here is another great YouTube video, this one demontrating how to make “Instant Ice”.

If you’ve ever used an instant hand warmer or a reusable heat pack, you’ve already seen and felt the same chemical process at work.

What’s going on?

Sodium acetate trihydrate crystals have a melting point of 58°C (136°F). When they are placed in water and heated to around 100°C (212°F) and then allowed to cool, the aqueous (water) solution becomes supersaturated. This means that the solution contains more of the dissolved crystals than it could normally hold.

This solution is capable of supercooling to below room temperature without forming crystals. This means that the solution remains in a liquid state well below its normal freezing point.

A supercooled liquid will crystallize in the presence of a point of nucleation around which a crystal structure can form. In the video, simply touching the solution triggers it to crystalize into a solid again. The bond-forming process of crystallization is exothermic meaning that it releases heat energy. Sodium acetate heat packs can be easily “recharged” by boiling until all the crystals are dissolved again.

Please Note: It is very important that when you transfer the heated solution to the container in which you cool it, you must leave any undissolved crystals behind. A single crystal will act as a point of nucleation to initiate crystallization of the entire batch once it begins to cool.

This is a pretty simple experiment to try at home. Sodium acetate is safe to work with - they wouldn’t use it in heat packs if it wasn’t. You can purchase Sodium Acetate Trihydrate from an educational & chemical supply outlet such as Ward’s Natural Science. Here is a link to their website.

More About Sodium Acetate:

Colorless crystals with slight vinegar odor. Soluble in water and ether, slightly soluble in alcohol. Readily available in 2 forms - I am told that either formulation should work for this experiment although the ratio of water to crystals necessary to achieve supersaturation will vary.

Sodium Acetate Trihydrate
Chemical Formula: NaOOCCH₃ - 3H₂O

Sodium Acetate Anhydrous (there is no water in this formulation)
Chemical Formula: CH₃COONa

Other uses for Sodium Acetate - Manufacturing of dye and coloring, preservation of meat products, purification of glucose, electroplating, tanning, dehydrating agent (dessicant), soap-making, photography and as a food additive.