Solutions used in argentometric titrations

Two most important solutions used in argentometric methods are solution of silver nitrate and solution of potassium thiocyanate.

Silver nitrate solution

Silver nitrate solution of known concentration can be prepared using pure solid AgNO₃, after drying it (see standard substances used in precipitation titrations section). Most popular solution is that of 0.1M concentration, although for determination of small amount if chlorides more diluted solutions can be used (0.02M). However, use of diluted solutions should be preceded by thorough analysis of possible titration errors. This is especially important in the case of Mohr titration, where some excess of silver must be added before red silver dichromate precipitates and signals end point.

Silver nitrate solutions slowly decompose when exposed to light, so they should be kept in dark bottles.

Potassium thiocyanate solution

Potassium thiocyanate is not used as a standard substance. Its solutions are prepared by dissolving solid KSCN and standardized against solution of silver nitrate of known concentration. Usually used solution is 0.1M.

Potassium chromate solution

5% w/w potassium chromate solution is used as an indictaor in titration with silver nitrate.

Nitric acid 1+1

About 40% solution of nitric acid, used for acidification of the chlorides solution in Volhard method. 1+1 means simply 1 volume of the acid and 1 volume of water.

Ammonium ferric sulfate solution

10% w/w ammonium ferric sulfate (FeNH₄(SO₄)₂, iron alum) is a convenient source of Fe³⁺ cations, used for detection of excess thiocyanate. This solution is acidified with nitric acid to avoid iron (III) hydroxide precipitation.