Mercuric Nitrate reacts with Chloride ions to form soluble, mostly undissociated Mercuric Chloride, and is commonly used in the determination of Chloride. Diphenylcarbazone (DPC) is used as the indicator:
Hg2+ + 2 Cl- → HgCl2 (undissociated)
excess Hg2+ + DPC → [HgDPC]2+ (blue-violet complex)
While the Mercuric Nitrate titrimetric method for determining Chloride is the official or approved method in some States, the use of the less toxic and environmentally less harmful Silver Nitrate is a more popular method of Chloride determination.
Mercuric Nitrate solutions can be standardized with a standard Chloride solution, using Diphenylcarbazone (DPC) as an indicator. A pH indicator, such as Bromophenol Blue or Xylene Cyanol FF, can be added to the Diphenylcarbazone Indicator to show if the pH is in the proper range for the titration.
Mercuric Nitrate solutions can also be standardized with standard Thiocyanate solution, using Ferric Alum as the indicator:
Hg2+ + 2 SCN- → Hg(SCN)2 (white precipitate)
excess SCN- + Fe3+ → [FeSCN]2+ (red complex)