Neutralizing an acid. Powdered calcium hydroxide (Ca(OH)2, slaked lime) is added to a beaker with 0.1 M solution of hydrochloric acid (HCl) that has few drops of universal indicator added. Initially color is red, indication an acidic solution (left frame). When calcium hydroxide is stirred in, it dissolves, neutralizing the acid, and color turns green, indicating a neutral solution (right frame). The reaction is HCl + Ca(OH)2 -> CaCl2 + H2O.