British Science Week: Home science experiment – making hot ice
With this experiment, we will show that a substance could be created that was a liquid at room temperature but, when it was disturbed, would immediately crystallise and form what is known as hot ice.
Hot ice is an amazingly cool substance and the ingredients required are easy to obtain. However, it is difficult to make, and you probably won’t get it right on your first attempt, but don’t give up hope. You can either re-melt any failed hot ice or start again, making sure to follow the method carefully.
This is a great experiment to do at home and an even better one to do at school. You can directly see the effects of crystallisation and there’s plenty of science embedded into the fun of seeing hot ice in action. If you do replicate our experiment, make sure you send us some photos on Facebook or Twitter so we can see how it went!
You will need
1 litre of clear vinegar
4 tablespoons of baking soda
First, a litre of clear store-bought vinegar must be measured out. This must be clear, as brown vinegar contains impurities that will prevent the experiment from working. Next, you need to add about three to four tablespoons of baking soda (sodium bicarbonate) to the vinegar. This has to be done slowly, as the reaction can make the liquid explode over the side of the container. Stir this until all the baking soda is dissolved and then put the mixture on to the hob to boil.
You need to get rid of about 90% of the liquid, so leave it to boil for over 30 minutes. You’ll start to notice a white substance on the side of the pan. This is sodium acetate, and a bit of this needs to be saved for later use. Eventually, a crust (sodium acetate anhydrous) will begin to form on the liquid. At this point, take it off the boil and transfer it into a container. This must be immediately covered to prevent the substance crystallising. You then need to cool it, so place it in an ice bath for 15 minutes or a fridge for a bit longer.
The liquid needs to cool below room temperature. This makes it into a supercool liquid that will exhibit the characteristics of hot ice. Once it’s cooled, you can take the lid off and put some of the white sodium acetate collected earlier in the liquid.
The points where sodium acetate is introduced will begin to crystallise. After a few seconds the entire liquid will appear to freeze. However, when touched, the substance is hot and not cold because the process of crystallisation here is exothermic, so heat is given off as the liquid solidifies. So, what’s happened in this experiment?
Almost every substance has a freezing point, but for something to solidify the molecules must rearrange from a liquid to a solid or crystal arrangement. However, hot ice, or sodium acetate trihydrate, is a supercool liquid where the molecules do not rearrange until they are disturbed, in this case by introducing sodium acetate. Hot ice melts at 58 degrees Celsius and is a crystalline solid at room temperature, allowing this effect to be produced as the baking soda and vinegar are heated. The unarranged molecular structure results in the occurrence of this crystallisation effect. You can re-use your hot ice by adding vinegar until the solid crystals are fully dissolved and repeating our method again.
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