= Solution
The historical names identify <potassium chlorate>, <ammonium nitrate> and <calcium carbonate>. Their expected net <thermal decomposition> <chemical equations>, written in modern formulae, are
$$
\boxed{2\mathrm{KClO}_3\xrightarrow{\Delta}2\mathrm{KCl}+3\mathrm{O}_2,}
$$
$$
\boxed{\mathrm{NH}_4\mathrm{NO}_3\xrightarrow{\Delta}\mathrm{N}_2\mathrm{O}+2\mathrm{H}_2\mathrm{O},}
$$
and
$$
\boxed{\mathrm{CaCO}_3\xrightarrow{\Delta}\mathrm{CaO}+\mathrm{CO}_2.}
$$
The first gives <potassium chloride> and <oxygen>. A <potassium perchlorate> intermediate can occur during uncatalysed heating; the first <chemical equation> gives the final overall balance. The second represents the familiar <nitrous oxide> pathway, with hot <water> initially as vapour. It does not mean that <ammonium nitrate> has only one decomposition pathway: conditions, impurities and confinement can produce different <gases> and violent decomposition.<Chemical Advisory on Ammonium Nitrate by United States Environmental Protection Agency>[Decomposition Chemistry: dependence on heating, contamination and confinement]{ref}
The third is <calcination> of <limestone> to <quicklime>. Its extent depends on <temperature> and the <partial pressure> of <carbon dioxide>; removing <carbon dioxide> favours further decomposition. Reversing the process gives carbonation of <calcium oxide>.
For dissolution in <hydrochloric acid>, the corresponding balances are
$$
\boxed{\mathrm{Zn}+2\mathrm{HCl}\longrightarrow\mathrm{ZnCl}_2+\mathrm{H}_2,}
$$
$$
\boxed{\mathrm{MgO}+2\mathrm{HCl}\longrightarrow\mathrm{MgCl}_2+\mathrm{H}_2\mathrm{O},}
$$
and
$$
\boxed{\mathrm{Al}_2\mathrm{O}_3+6\mathrm{HCl}\longrightarrow2\mathrm{AlCl}_3+3\mathrm{H}_2\mathrm{O}.}
$$
“Magnesia” here means <magnesium oxide>, and “alumina” means <aluminium oxide>. <Zinc> undergoes an <oxidation-reduction reaction>, reducing <hydrogen ions> to <molecular hydrogen>. The oxides instead undergo <acid-base reactions>: <hydrogen ions> convert oxide into <water>, without <hydrogen> evolution. The chlorides are dissolved species in <water>, rather than anhydrous molecular salts necessarily existing intact in the solution. Strongly ignited <aluminium oxide> may dissolve slowly; the balance does not determine the rate.
Back to article page
