everyday chemistry - Why do some materials turn black and others white after combustion?

Most solids objects turn black after they are burnt. But some turn white. Why is that ?

Answer

The objects which turn black are usually carbon based/organic compounds. When burned/combusted they follow one of the following unbalanced reactions: \begin{align} \ce C_x(\ce H_y\ce O_z)_\text{(solid/liquid)} + {\ce{O2}}_\text{(gas)} &\ce{->} \ce C_\text{(solid)} + \ce{H_2O}_\text{(liquid)} + {\ce{CO_2}}_\text{(gas)}\\ \ce C_x(\ce H_y\ce O_z)_\text{(solid/liquid)} + {\ce{O2}}_\text{(gas)} &\ce{->} \ce{H2O}_\text{(liquid)} + {\ce{CO2}}_\text{(gas)}\\ \ce C_x(\ce H_y\ce O_z)_\text{(solid/liquid)} + {\ce{O2}}_\text{(gas)} &\ce{->} \ce {H2O}_\text{(liquid)} + {\ce{CO2}}_\text{(gas)} + \ce{CO}_\text{(gas)} \end{align}

You'll notice that some of the reactions will produce solid carbon, which is the black thing you see.

On the other hand, inorganic compounds begin to decompose into their ions and/or release their "trapped" water molecules. As you'll notice, most ionic compounds are white solid salts.