What is the purpose of heating the precipitate mixture of barium sulphate for an hour over a stem bath?
Answers
Explanation:
Alternative Precipitation
The direct amplification of silver can be carried out by precipitation with chromate. Ag2CrO4 is filtered and then treated with barium chloride for the precipitation of both BaCrO4 and AgCl. These precipitates are treated with Ag+ and thus 1 mol of Ag2CrO4 and 2 mol of AgCl are formed.
The process can be repeated, and on each treatment with BaCl2 an amount of silver chloride equivalent to twice the original silver chromate is produced; after n cycles 2(n+1) moles AgCl can be found.
This procedure can also be applied for the indirect determination of CrO42−, by measuring the AgCl obtained.
One other indirect amplification, similar to those mentioned, is the amplification of phosphate by precipitation of silver phosphate and its conversion to silver chromate.
A particular case of the alternative precipitation method, which Weisz called cyclic amplification by fixation of both ions of an amplifiable compound, requires that the substance to be amplified be subjected to a series of stoichiometric reactions in order to enhance its mass.
Scheme 5 for the amplification of hexacyanoferrate(II), via precipitation of the silver salt and formation of silver chloride and Prussian Blue by reaction with iron chloride, shows that it is a particular case of the alternative precipitation method in which the amplification takes place by a cyclic procedure.
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Scheme 5.
This is an indirect procedure, but silver can also be amplified in a direct way by measuring the final AgCl formed.
Weisz has applied this type of amplification reaction to the determination of phosphate, hexacyanoferrate(II), chromate, zinc, iron, and silver, and has obtained amplification factors up to 153 in a series of cyclic processes carried out in an automated form.