The following guidelines are generalizations. A substance is classified as insoluble if it precipitates when equal volumes of 0.1 M solutions of its components are mixed. Keep in mind, however, that no substance is completely insoluble.
Substances listed as insoluble are, at some level, partially soluble.
For example, NH 4 OH is a soluble compound. Na 2 SO 4 is completely soluble. For example, Na 2 S is soluble, MnS is insoluble.