Copper sulfate pentahydrate is sky blue color, its aqueous solution is weak acid, commonly it is known as stone gallbladder, blue alum. Copper (II) sulfate, also known as copper sulphate, are the inorganic compounds with the chemical formula CuSO4(H2O)x, where x can range from 0 to 5. The pentahydrate (x = 5) is the most common form. The pentahydrate (CuSO4·5H2O), the most commonly encountered salt, is bright blue.