Here is an experiment which definitely has a wow factor, and was highly entertaining for us at home today. This is how you can take two normal pantry staples - white vinegar and bicarb soda, and create something very special.
This experiment involves a few concepts: chemical reactions, crystallisation, exothermic and endothermic reactions and supercooled liquids.
Basically what you will do is combine vinegar and bicarb soda from your pantry to create a sodium acetate solution. You then reduce the solution till it is very concentrated, and you have removed most of the water. This solution is then "supercooled", meaning that you have cooled it below its freezing point but kept it in a liquid state. For a sodium acetate solution this happens when it gets to below 15 degrees Celcius. If there is no "nucleation site" for the crystals to begin to grow, then the solution will stay as a supercooled liquid. As soon as it comes into contact with something for the crystals to grow off (a nucleation point), it will instantly form crystals, in this case when you pour it out! The formation of sodium acetate crystals is an exothermic process, meaning it gives off heat - so you will end up with "hot ice".
This experiment is a bit fiddly - but very hard to actually stuff up. If you keep on trying you'll definitely get it to work.
To make hot ice you will need:
4 cups of white vinegar (it needs to be white vinegar otherwise it will have impurities in it which can stop the crystallisation process)
4 tablespoons of bicarb soda
a glass jar or a jug
a plate
Step 1: Put the 4 cups of vinegar into a large saucepan, and add the 4 tablespoons of bicarb. Add it very slowly or else it will bubble completely over the edge of the pan. We used a 3L saucepan which worked well. Adding bicarb to vinegar creates two new chemicals - sodium acetate, and carbon dioxide (the bubbling is the carbon dioxide coming out).
Step 2: Once the bicarb is dissolved heat it up and reduce it. You will need to keep it on a medium to low heat for about an hour or more - till you have about 3/4 cup of solution left. If you heat it too high or fast it will turn yellow (as ours did!). It doesn't matter in terms of results, it just doesn't look as good.
Once it is getting close you should have white powdery crystals on the sides of the pan (don't worry they wash off really easily). Don't wash them away yet!! You will need them!
Step 3: Pour the 3/4 cup of liquid left in the pan into a smooth, clean glass jar or jug. We used a pyrex jug. Pop this in the fridge or the freezer, depending on how fast you want to go. You need to cool it down to 15oC or lower without bumping it. This will take about an hour in the fridge and half an hour or so in the freezer.
Step 4: While the solution is cooling, scrape a few of the crystals from the side of the pan into the middle of the plate or container you will use to make your ice tower. We used a pyrex baking dish.
Step 5: When your solution is cooled (when the jar or jug feels pretty cold), remove it from the fridge and very carefully take it to your prepared dish with the crystals on it. Do not jiggle or bump the jug - we did and this happened! Any bump can start off the crystallisation process.
We accidentally started off the crystallisation process in the jug, meaning that our solution completely crystallised in the jug, If this happens just reheat it, and repeat the cooling process. We had to restart a few times - it will still work. And it is amazing to see the crystals grow before your eyes, moving out in circles, and in long shards.
Step 6: Little by little pour some of the solution onto the pile of crystals in your dish. As they make contact with the crystals the supercooled solution will instantly crystallise before your eyes!
Get the kids to touch the ice! It is really warm!! The crystals are quite soft and crumble easily. If you want to, melt the crystals again in the pan and repeat the process.
WHAT TO DO IF IT DOESN'T WORK:
Don't worry. You can reheat and reboil this HEAPS of times. We reheated about 4 times to get around various problems... Remember all you are aiming for is a COLD solution and one which is very concentrated. More boiling will make it more concentrated and leaving it in the fridge longer will cool it further.
1 - If the crystals don't form, don't worry. Return the liquid to the pan, add a little more vinegar and reduce it again, this time a little more than you did at first.
2 - You didn't get any crystals on the side of the pan. Reboil it! You'll get some powder if you go far enough.
3 - The bicarb soda doesn't all dissolve - add some more vinegar.
4 - Your bicarb solution overflows... work out approximately how much you've lost. You might just have to reduce it a bit less than to 3/4 cup.
5 - Your solution doesn't crystallise again and again... keep reducing it, or try cooling it down more. If it is not concentrated enough, OR if it doesn't reach the supercooled state, it will not work. You can keep reducing and cooling it again and again without ruining it.