Sulfides are generally insoluble. The alkaline earth metals are soluble. Each rule has exceptions and the important ones are noted. The periodic trend in the solubility of alkaline earth metal compounds is that as one goes down a group, it increases in activity. Colours of metal sulfides are important in identifying compounds in inorganic chemistry. If you study the periodic table, you will know compounds of the top element in a group are often different from the others. Most of the precipitation reactions that we will deal with involve aqueous salt solutions. All alkali metals sulfide and alkaline earth metals sulfides are soluble in water and form colourless aqueous solutions. Solubility Patterns in the Periodic Table continued 2 216 linn Scientiic nc ll ihts esered 4. SOLUBILITY RULES. Add 1 mL (about 25 drops or fill the well about 1⁄ 4 inch or 0.5 cm deep) of an alkaline earth metal chloride solution to each well in a horizontal row, as follows (see Figure 1): ... insoluble and slightly soluble plus a good set of rules for solubility at the end of the file. so your answer becomes BaSO4