The chlorate is reduced to chloride, and the latter is determined as silver chloride, AgCl. The reduction may be performed with iron(II) sulphate solution, sulphur dioxide, or by zinc powder and acetic (ethanoic) acid. Alkali chlorates may be quantitatively converted into chlorides by three evaporations with concentrated hydrochloric acid, or by evaporation with three times the weight of ammonium chloride.
The chlorate solution should have
a volume of about 100 mL, and contain about 0.2 g C1O3. Add 50 mL of
a 10 per cent solution of crystallised iron(II) sulphate, heat with constant
stirring to the boiling point, and boil for 15 minutes. Allow to cool, add
nitric acid until the precipitated basic iron(III) salt is dissolved,
precipitate the chloride by means of silver nitrate solution, and collect and
weigh as AgCl after the usual treatment .
Alternatively, treat the chlorate solution with excess of sulphur dioxide, boil the solution to remove the excess of the gas, render slightly acid with nitric acid, and precipitate the silver chloride as above.
For the reduction with zinc, render the chlorate solution strongly acid with acetic acid, add excess of zinc, and boil the mixture for 1 hour. Dissolve the excess of unused zinc with nitric acid, filter, and treat the filtrate with silver nitrate in the usual manner.
Note. Hypochlorites and chlorites may be reduced to chlorides with sulphur dioxide, and determined in the same way.