Determination of Chloride by Precipitation with Silver Nitrate (Gravimetry)
This method determines the chloride ion concentration of a solution by gravimetric analysis. A precipitate of silver chloride is formed by adding a solution of silver nitrate to the aqueous solution of chloride ions. The precipitate is collected by careful filtration and weighed.
Ag+(aq) + Cl-(aq) --> AgCl(s)
The precipitate can be collected more easily if the reaction solution is heated before filtering. This causes the solid silver chloride particles to coagulate. The precipitation is carried out under acidic conditions to avoid possible errors due to the presence of carbonate and phosphate ions which, under basic conditions, would also precipitate with the silver ions.
As the method requires very careful weighing of the samples, it is best to use it on solutions that are known to contain a fairly significant concentration of chloride ions, such as seawater which is used as the example here. For this reason it should not be used for stream or river water.
To download a printable version of this experiment (in pdf format) use the link below.
Chloride Gravimetry (PDF 104kb)
Please note that Outreach support for these experiments is limited to NZ school students and teachers, and we are unable to answer queries from overseas.