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I am trying to isolate pure carbon in its elemental form. Are there any decomposition reactions or other easy to carry out reactions to yield solid carbon? and in the case that it is isolated, does it start reacting with other elements in the air?

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A classic reaction to yield carbon is the dehydration of sucrose (table sugar) with concentrated sulfuric acid: Put some sugar in a beaker, carefully add sulfuric acid and watch a voluminous "snake" of porous carbon (blow up due to the steam released during the reaction) from the beaker.

You'll find lots of videos on this on youtube or other platforms.

Note that this is performed with concentrated sulfuric acid! If you decide that you must do this at home, protect yourself (googles, gloves, lab coat) and keep the sulfuric acid locked away.

But there's a more simple way to yield carbon:

Hold a spoon (with a long handle) into the flame of a candle. The black stuff that deposits on the spoon is carbon. Play with the distance for optimal results.

As far as the reactivity of carbon is concerned: There's no danger in that! Millions of people stockpile carbon in the form of coal at home in their cellars or sheds for heating.

And actually, this points to the easiest and most safe option: Don't perform any reaction at home and grind some charcoal or anthracite coal instead.

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    $\begingroup$ If concentrated sulphuric acid is on the table, wouldn't it be possible to get very pure carbon by taking a pencil lead, crushing it into dust and then submerging it in the acid for a while? Not much other than the pure graphite could survive that. Bonus points for being a single allotrope! The candle soot is what I had first thought, but while it is a very simple and convenient procedure, the soot isn't exactly pure carbon. $\endgroup$ – Nicolau Saker Neto Mar 7 '15 at 22:25
  • $\begingroup$ @NicolauSakerNeto You're probably right. The clay used as a binder won't survive. $\endgroup$ – Klaus-Dieter Warzecha Mar 7 '15 at 22:29
  • $\begingroup$ @NicolauSakerNeto Purity is a relative term. Doesn't make any sense to make statements what is pure what is not without reference to purity level and what kind of impurities we care. Natural graphite in penciles is not an "absolutely pure" substance either. $\endgroup$ – Greg Mar 8 '15 at 2:37
  • $\begingroup$ Sorry I know this is definitely not the most technical or probably correct term, but in the sucrose and sulfuric acid reaction, why does the carbon product look 'wet' and not very compact as other carbon based materials like charcoal pellets or solid graphite rods. $\endgroup$ – AlanZ2223 Mar 8 '15 at 12:19
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    $\begingroup$ @AlanZ2223 During the dehydration of sucrose with sulfuric acid, alot of heat is released - enough to convert the water (= reaction product) to steam. As a consequence, the carbon adopts a foam-like structure - the carbon is build around bubbles of water vapour. When the mass cools down, the water condenses and forms a wet film on the carbon surface. In addition, traces of sulfuric acid dragged out of the mix might add to the wet look. $\endgroup$ – Klaus-Dieter Warzecha Mar 9 '15 at 5:04
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Why don't you just buy activated carbon? Generally it is rather pure and contains no carcinogen or poisonous substances, so it is very safe to handle, unlike most pyrolysis products.

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  • $\begingroup$ Well I wanted to perform an experiment, just for the whole funs and what not. $\endgroup$ – AlanZ2223 Mar 8 '15 at 12:12
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You should be able to drive off water from a pure carbohydrate (like sucrose) simply by heating it enough. Think of it as a very simple example of destructive distillation.

If you prefer something a bit more exotic, you could ignite a magnesium strip and drop it onto a block of dry ice. The magnesium will combine with the oxygen, leaving carbon soot. I'm not sure how easy it would be to collect that soot, though, or to separate it from the magnesium oxide co-product.

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