When the concentration increases to 30% - 40%, the solubility reaches the maximum value. If the concentration continues to increase to 50%, the solubility of iron suddenly drops ten thousand times, and its surface is in a special state. This phenomenon is called passivation. However, it does not always occur in oxidizing media, but magnesium can be passivated in hydrofluoric acid, phase and inscription in hydrochloric acid [1]
