Phosphorus salt pearl
The phosphorus salt bead , like the borax bead , is used as a preliminary sample for some metal cations as part of the separation process in the qualitative analysis in chemistry . For this purpose, a magnesia stick is heated in the Bunsen burner and held in the phosphorus salt NaNH 4 HPO 4 · 4 H 2 O (sodium ammonium hydrogen phosphate). Now it is heated in an open flame until the phosphorus salt melts into a pearl. This process is repeated until a pearl with a diameter of approx. 3-4 mm has formed. When the phosphorus salt is heated, ammonia and water are expelled and the phosphorus salt changes to meta- or polyphosphate, (NaPO 3 ) x (x = 3–8). If you add a heavy metal salt, heavy metal phosphates are formed, some of which have characteristic colors. Based on the color of the pearl, statements can be made about the ingredients of the analysis.
The colors of the phosphor salt pearl correspond to those of the borax pearl .
| cation | Oxidizing flame | Reduction flame |
| Ag + | silver-white | |
| Fe 2+ ; Fe 3+ | red-brown | greenish |
| Mn 2+ | violet | colorless |
| Co 2+ | blue | blue |
| Ni 2+ | yellow | Gray |
| Cr 3+ | green | green |
| Al 3+ | colorless | colorless |
| Cu 2+ | hot: yellow, cold: blue | hot: colorless, cold: red-brown |
| Ti 4+ | hot: yellowish, cold: colorless | colorless |
swell
Jander-Blasius, textbook on analytical and preparative inorganic chemistry, 8th edition, S. Hirzel Verlag Stuttgart, 1969
Web links
- Reaction equations and colors of the phosphor salt and borax pearl ( Memento from September 26, 2007 in the Internet Archive ), p. 127 (PDF file; 1.87 MB)