Make Hot Ice - Heating Pad Chemistry

Make Your Own Chemical Hot Pack

Sodium acetate is called hot ice because it's hot and resembles an ice cube. The chemical can be used to make hot packs.
Sodium acetate is called hot ice because it's hot and resembles an ice cube. The chemical can be used to make hot packs. ICT_Photo / Getty Images

Here's an easy chemistry project you can do in which you take a clear liquid and instantaneously solidify it into hot 'ice'. It isn't water ice, however. This is how you make crystals of sodium acetate, which is used in hand warmers and chemical heating pads and hot packs.

Hot Ice Materials

  • sodium acetate
  • water
  • saucepan
  • glass or pan

Making Your Own Sodium Acetate Monohydrate

If you don't have any sodium acetate monohydrate you can make your own. Add baking soda (sodium bicarbonate) to vinegar (weak acetic acid) until the mixture stops fizzing. This will give you an aqueous solution of sodium acetate. If you boil off the water, you'll be left with the sodium acetate. Expect to use a lot of baking soda and vinegar if you go this route.

Make the Hot Ice

What you are going to do is make a supersaturated sodium acetate solution. The solution will remain a supercooled liquid until a little solid sodium acetate is introduced. This will cause rapid crystallization that will resemble a block of ice, except it will be hot to the touch and not edible.

  1. Dump some sodium acetate monohydrate into a saucepan.
  2. Add just enough water to dissolve the sodium acetate.
  3. Heat the solution to just below its boiling point.
  4. Stir in more sodium acetate. Keep stirring and adding sodium acetate until you start to see solid material accumulating at the bottom of the pan.
  5. Pour the hot solution into a glass or other container. Do not allow any of the undissolved solid to enter the container.
  6. Cool the solution in the refrigerator 30 minutes to an hour.
  7. Remove the solution from the refrigerator. As long as you didn't leave any solid sodium acetate in the solution, it should still be liquid.
  8. When you are ready to make 'ice' introduce a little of the solid sodium acetate. You could dip a toothpick or the edge of a spoon in sodium acetate powder.
  9. The crystallization will evolve heat (exothermic reaction), making the solid feel hot to the touch (~130° F).

Hot Ice Trick

You don't have to solidify the sodium acetate in a dish. You can crystallize it as the solution is being poured to make fantastic shapes.