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, CxHy)

  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)