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Char is made of Carbon, but just because a substance char, does it immediately mean it contains carbon?

Also, Why is charring not a good test for detecting carbon in organic compounds? I searched that because the test can't differentiate an elemental carbon from an organic carbon. Can someone elaborate or give an example?

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  • $\begingroup$ Other compounds also char, not just carbon. Also, some carbon compounds won't char. That is why it is is a poor test. $\endgroup$
    – matt_black
    Feb 8 '18 at 18:13
  • $\begingroup$ If you can fix CO2, than definitely your sample contains C in a form or another. For the rest see answer. If in concomitance with CO2 you see water, this point to organics. By the way, I won't check for carbon in organic compounds. I would rather check if they are organic and flame as well as conc. Sulphuric acid do quite well to this end. $\endgroup$
    – Alchimista
    Feb 9 '18 at 10:38
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Not all carbon-containing chemical char. For example, sodium carbonate, $\ce{Na2CO3}$ just produces $\ce{CO2}$. Sodium carbonate might be viewed as inorganic, though.

An organic chemical that behaves in a similar way is hexamethylenetetramine, or hexamine, $\ce{(CH2)6N4}$. On heating, it decomposes primarily into formaldehyde, $\ce{H-CHO}$, and ammonia, $\ce{NH3}$, though there are traces of other gases such as $\ce{HCN}$ and $\ce{CO}$. For that reason, hexamine is used as a smokeless fuel (no char left behind, as the saying goes).

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