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why do we add boiling chips or boiling stones before the distillation starts? Boiling chips should never be added to a hot solution!Why?

i don't know what the answer is to the first one, but as for the second i think i have a clue. is it that the boiling chips will start a violent boiling action that can hurt the person conducting the experiment?

  • chem -

    Your answer to the second one is correct and if you think a little you will see that's why you add boiling chips to the solution FIRST (before distillation is started).
    Solvents have a tendency to overheat and it is possible to heat a solvent to a higher temperature than its boiling point BUT the solvent doesn't boil. This is called a superheated solution (solvent)--whatever. Anyway, the boiling chips have tiny broken edges/small spicules/adsorbed air/etc. These edges/air causes the solvent to be more active at those sites and the solvent does not become superheated (most of the time). It stops the "bumping" that superheating causes. If you wait until the solvent is already superheated, THEN add the boiling chips, you suddenly provide the means for the solvent to boil, it "bumps" and is likely to come out of the distillation apparatus violently. That can cause burns/eye damage/ etc. I had to regularly prepare pure H2SO4 by distillation when I was in grad school. It became superheated easily and we could not use boiling chips because they contained impurities which is why we were distilling it in the first place. We put jackets around the apparatus and stayed on the other side of the lab so that if it bumped out of the apparatus we wouldn't be in the path. We certainly didn't want boiling H2SO4 down out neck!

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