reactions at heating.

1. When the substance to investigate is heated in a dry, suitable tube, then this may have the consequence that the substance will decompose. The substance has in this case no melting point / boiling point. We talk aboutr thermolysis.
   Sometimes you can do observations during this process that give information about the substance; you can draw conclusions about the character of the substance. Normally we start with carefull heating, followed by very strong heating. Take note of:
   If water vapor escapes, the substance might be a hydrated salt, like Copper(II)sulfate or soda. But it could also be a hydroxyde.
   Examples:
   • CuSO₄.5H₂O (blue) CuSO₄ (white) + 5H₂O(g)
   • Cu(OH)₂(s)(blue) CuO(s)(black) + H₂O(g)
   • 2CuOH(s)(green) Cu₂O(s)(reddish brown) + H₂O(g)
   • 2AgOH(s)(brown) Ag₂O(s)(black) + H₂O(g)
   
   
2. If, after strong heating, remains a black residue (coalish), this means that the substance contained Carbon. Probably it was an organic substance, one from the carbon chemistry.
   C₆H₁₂O₆(s) > C(s) + gases (like H₂O, CO₂, C_xH_y)
   
   
3. Some salts - at heating - change into the metal oxyde and one or more gases. This way for example, nitrates give the so called 'nitric vapors', and carbonates give Carbon dioxyde.
   
   • Pb(NO₃)₂(s)(wit) PbO(s)(orange) + NO₂(g) + NO(g) + O₂(g) (brownish nitric vapors)
   • CaCO₃(s)(white) CaO(s)(white) + CO₂(g)