Alums are considered double salts formed from two different metal ions and the sulfate ion, while tetraoxosulphate (VI) acid, or sulfuric acid, can produce both normal and acidic salts due to its two replaceable protons. For example, sodium sulfate is a normal salt, and sodium bisulfate is an acidic salt. The ability to form these two types of salts illustrates the versatile properties of sulfuric acid in chemical reactions. ;