If standard solutions with known chloride ion concentration are available for comparison, the amount of precipitate can be used to estimate the concentration of chloride ions. When a few drops of a silver nitrate solution are added to a slightly acidic aqueous solution that contains chloride ions, a white precipitate of silver chloride will form. The test for chloride ions described here is based on precipitation of an insoluble chloride salt. A relatively simple test for chloride ions is needed to decide when the bath needs replacing or when the treatment can be stopped. (2013) recommend stopping iron treatments when the chloride ion concentration is less than 5 parts per million (ppm). In practice, the bath has to be replaced regularly, because it becomes less effective as chloride ions build up in it. The treatment is straightforward, in principle: the objects are soaked in an alkaline bath until the chloride ions from the objects are dissolved into the bath (Selwyn 2004). Removing the chloride ions is an important step for conservators in treating chloride-contaminated objects. Chloride ions accelerate the corrosion of iron, as is all too familiar to anyone who drives a car on roads that are de-iced with road salt (mainly sodium chloride). This contamination is particularly dangerous for objects that contain iron (Selwyn et al. Objects recovered from marine or burial sites may be contaminated with high concentrations of chloride ions, as described in Sources of salts in objects.
#Silver nitrate charge pdf#
Abbreviations CCI Canadian Conservation Institute PDF portable document format ppm part per million Symbols μS/cm microsiemens per centimetre Ag silver AgCl silver chloride Cl - chloride ion g gram g/mL gram per milliliter HNO 3 nitric acid M molarity mg milligram mL millilitre mm millimetre pH potential of hydrogen v/v volume per volume w/v weight per volume Introduction
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