Halides and pseudohalides with silver nitrate

Chemicals needed

distilled water

potassium bromide Xi

potassium chloride

potassium cyanate Xn     R 22    S 24/25

potassium iodide

potassium thiocyanate Xn     R 20/21/22-30    S 13

silver nitrate solution, diluted  Xi    N    R 34-50/53     S(1/2)-26-45-60-61

Instead of potassium salts one can use the corresponding sodium salt. If not all salts are available the experiment can be accordingly adjusted.

Production of silver nitrate solution

Equipment needed

test tube rack
for each salt one test tube

Test procedure

• One adds to each test tube a small spatula-tipful of one of the different salts.
• To each salt one adds 2-3 ml of water, the salts dissolve.
• To each salt one adds a couple of drops of silver nitrate solution, various precipitations are produced:
  • Chloride, cyanat und thiocyanat cause white precipitations.
  • Bromide causes a sallow yellow precipitation (a differentiation to chloride is only possible in exceptionally good lighting conditions).
  • Iodide causes a yellow precipitation.
  • The halide precipitations form under gentle swaying a rather homogenous suspension which only slowly clarifies, the pseudohalide precipitations are formed very quickly.

Disposal

One disposes of the suspensions as silver-containing waste. If one does not collect this seperately, then as heavy metal waste, it is not to be discharged into the drainage.

Elucidation

The halides and pseudohalides of silver are insolube and precipitate. In weighing the deposits, one can also determine quantatively the halides/pseudohalides or silver ions.

Photos

Precipitation of halides and pseudohalides. From left to right: chloride, bromide, iodide, cyanate, thiocyanate.

Literature

The experiment is based on an experiment from the school class.

Concerning the precipitation of cyanide: XII.2.1, "Cyanidnachweis als AgCN", S. 141, [3]