Nitric acid (HNO) greatly enhance the rate of reaction. Although chromium (Cr), iron (Fe), and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal-oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called passivation. Typical passivation concentrations range from 20% to 50% by volume (see ASTM A967-05). Metals that are passivated by concentrated nitric acid are iron, cobalt, chromium, nickel, and aluminium. Being a powerful oxidizing acid, nitric acid reacts violently with many organic materials and the reactions may be explosive. The hydroxyl group will typically strip
Brønsted–Lowry acid–base theory conjugate acid of the base in the first reaction and the conjugate base of the acid. In the above example, acetate is the base of the reverse reaction and hydronium ion is the acid. The power of the Brønsted–Lowry theory is that, in contrast to Arrhenius theory, it does not require an acid to dissociate. The essence of Brønsted–Lowry theory is that an acid only exists as such in relation to a base, and "vice versa". Water is amphoteric as it can act as an acid or as a base. In the image shown at the right one molecule of