The anion to be determined is precipitated as the silver salt the precipitate is collected and dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia/ammonium chloride buffer. The procedure involved in the determination of these anions is virtually that discussed in Section 10.58 for the indirect determination of silver. The buffer has excellent keeping qualities, sharp end points are obtainable, and the strong ammonia solution is completely eliminated. The monoethanolamine- hydrochloric acid buffer has a buffering capacity equal to the ammonia-ammonium chloride buffer commonly employed for the titration of calcium and magnesium with EDTA and solochrome black (compare Section 10.54). Silver halides can be dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia-ammonium chloride buffer, and the nickel ion set free may be titrated with standard EDTA using murexide as indicator. 0.88-0.90) to 17.5 g ammonium chloride and diluting to 250 mL with de-ionised water. Prepare an ammonia-ammonium chloride buffer solution (pH 10), by adding 142 mL concentrated ammonia solution (sp. The pH of 10 is attained by the use of an aqueous ammonia-ammonium chloride buffer mixture.
This is the basis of the indicator action in the EDTA titration.
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