Micro-chemical test for chloride

Author: Christine Bläuer

back to Micro-chemical testing

More information on the necessary equipment and materials see the Micro-chemistry article.

Procedure

The drop to be tested is acidified with a minimum of diluted nitric acid (HNO₃ 2M) and then a drop of silver nitrate 1% w/v solution is added. If Cl^- is present a white precipitate of AgCl will form instantly. After exposure to light this will turn brown with time. Detection limit for Cl- = 0.05µg.

Further observations

If sulfate is present typical silver sulfate crystals can be observed in the test drop.

If in addition to chloride, sodium or potassium are present in the solution, typical isotropic cubes of NaCl or isotropic rectangular, cruciform structures of KCl will form near the edge of the drop of the pure salt solution.

Ions that may inhibit the test or affect its sensitivity:

Iodide and bromide also produce white precipitates with silver nitrate solution, but these ions are not likely to be present in salt efflorescence from buildings.

crystallization of a dissolved salt