MadSci Network: Chemistry |
It depends a lot on what are the rules of the task. Do you have to get both substances back again? Or only one of them? Do you have to use a procedure that will leave the substances uncontaminated and safe to eat? When you have to separate two substances like salt and sand, it is fairly easy. Salt dissolves in water, and sand does not. So you shake up the mixture of salt and sand in water, and pour it through a filter. The sand is trapped in the filter, and salty water passes through. You can get the salt back by evaporating the water away from the solution that has passed through the filter. But this will not work for salt and sugar, because both salt and sugar are very soluble in water. One way around this problem is to use something other than water to dissolve one thing and not the other. Sugar will dissolve in petroleum spirit (I think you might call it paraffin in America? It is sometimes called white spirit too). Salt will not. So you could use the filtering and evaporation trick to separate them using petroleum spirit instead of water. But if you do that, the products might not be safe to use as food. There might be a lasting taint from the petroleum spirit even after it had all evaporated (because of impurities that would not evaporate). I certainly would not recommend it. You can recover salt that is safe to eat by another method, if you are prepared to sacrifice the sugar. Put the solid mixture into an old saucepan, and cook it up on the hottest gas burner you can manage for half an hour or so. You want the base of the saucepan glowing red! The sugar will burn. If you do the job thoroughly, it will burn away altogether, but more likely you will be left with a lot of soot as well as salt in the bottom of the saucepan. When you add water, the salt will dissolve. Any soot can be filtered off, and the salty water evaporated to recover quite edible salt. I can not think of any method of recovering sugar that I would be prepared to eat from a mixture of salt and sugar, especially not using things that would be available in most homes. But then -- this is not my exact field of scientific research :-) -- I am overweight, and shouldn't be eating sugar anyway ;-)
Try the links in the MadSci Library for more information on Chemistry.