Creating Instant Hot Ice

As this amazing science experiment video shows, sodium acetate crystals can be used to create 'hot ice' or 'instant ice' by dissolving them in boiling water.

Cooling this liquid and then touching it causes the solution to crystallize back into an ice-like solid. The reaction is exothermic which means it warms up and because of this sodium acetate is used commercially in a number of products including hand warmers.