[RisingEastStar17]

I reacted vinegar with sodium bicarbonate until it stopped bubbling. Then I heated it on a hotplate until the volume went from 100ml to about 60ml. I put it to cool in a fridge before taking it out. But there wasn't even a trace of a single crystal. Did I do something wrong?

[Aldebaran]

You did not say how much of each reactant you used (nor which was in excess) so you may not have evaporated enough of the solvent to produce crystals. Both sodium acetate and sodium bicarbonate are pretty soluble in water (125g/100ml and 96g/l respectively according to Wiki) so you may need to drive off quite a lot of the water to get a reasonable crop of crystals. Bear in mind vinegar is a very dilute solution of acetic acid typically about 5%.

[Borek]

To add to what Aldebaran wrote after bubbling stops I would add some acetic acid just to check there is no carbonate left. While excess acetic acid will easily evaporate on drying, leaving no residue, carbonate - if still present - will contaminate your product.