I would like to obtain some information about the following double salts: Potassium Nickel Sulfate Hydride, Potassium Cobalt Sulfate Hydride, Potassium Copper Sulfate Hydride, and Potassium Aluminum Sulfate Hydride (commonly known as Alum). What colors are they when dissolved, and what are their empirical forumulae? Thanks!
Potassium Nickel Sulfate Hydrate (not "hydride"), Potassium Cobalt Sulfate Hydrate, and Potassium Cupric Sulfate Hydrate all have the empirical formula
where M denotes the divalent cation (Ni, Co, Cu). In solution they are blue (green for Ni?).
Double sulfates of monovalent and trivalent cations are commonly called alums. They all have the formula
where M and N respectively denote the monovalent and trivalent cation. Crystalographic studies indicate that six of the water molecules surround the trivalent cation in an octahedral arrangement while the remaining six occupy cavities within this structure.The color of their solutions depends on the trivalent ion (e.g., white for Al, violet for Cr).