My experiment involves a reaction of magnesium in ribbon form with that of carbon dioxide. I know that the product shall be magnesium oxide (white powder) and carbon (black powder) but I do not know what kind of carbon it actually is (allotrope, purity, etc.)

It would also help if you can suggest a method for separating the carbon from the magnesium oxide after the reaction.

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    $\begingroup$ It is kinda graphite-like, but mostly amorphous, and quite impure (contaminated by $\ce{MgO}$ in the first place). As for separation, think of adding some acid. Also, welcome to Chem.SE. $\endgroup$ Mar 18 '17 at 7:03
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    $\begingroup$ If you just need to recover the MgO you could burn off the carbon by heating under oxygen. $\endgroup$
    – airhuff
    Mar 18 '17 at 18:14

The reaction you are working with is:

$$\ce{2 Mg(s) + CO2(g) -> 2 MgO(s) + C(s)}$$

where the carbon should be primarily graphitic.

Because you are producing two solids in this reaction, they will be physically intermixed and thus the purity of either solid will be poor, being contaminated with the other solid.

The separation of carbon from $\ce{MgO}$ is a fairly straight forward process, however. Upon contact with water, $\ce{MgO}$ becomes the basic $\ce{Mg(OH)2}$, which is readily soluble in dilute hydrochloric acid. Once the $\ce{MgO}$ has been dissolved in acid, you can filter off the acid-insoluble carbon. After the hydrochloric acid has been evaporated off, $\ce{MgO}$ will re-form from the $\ce{Mg(OH)2}$.


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