Lead Chlorate, Pb(ClO₃)₂

Lead Chlorate, Pb(ClO₃)₂.H₂O, is obtained by adding lead oxide or carbonate in excess to chloric acid solution, allowing the solution to stand for a day, and then filtering and concentrating the filtrate. The crystals are monoclinic, and are isomorphous with those of the corresponding barium salt, Ba(ClO₃)₂.H₂O. The salt may be dehydrated by heating under greatly reduced pressure to 130°-140° C. The manner of decomposition of anhydrous lead chlorate by heat is interesting because it may be compared with the familiar decomposition of potassium chlorate. The subject has been investigated by Sodeau, who has shown that chlorine is evolved together with oxygen, and that in the slow decomposition of the salt under 4 mm. pressure at 225°- 260° C. the following independent reactions take place:

Pb(ClO₃)₂ = PbCl₂ + 3O₂
Pb(ClO₃)₂ = PbO₂ + Cl₂ + 2O₂

and that lead peroxide and chlorine interact thus:

PbO₂ + Cl₂ = PbCl₂ + O₂,

so that the amount of chlorine actually evolved is much reduced. If the decomposition takes place rapidly at high temperature, the oxychloride PbO.PbCl₂ is formed.

The difference between the behaviour of lead and potassium chlorates when heated lies in the loss of chlorine by the former salt; and this difference may be attributed to the weaker basic nature of lead oxide. It may be suggested;that the nitrates show a somewhat similar difference when heated, potassium nitrate retaining all its nitrogen as nitrite, whilst lead nitrate loses it all as NO₂, and is converted into oxide.