GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
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 colour is red, indication an acidic solution (left frame). When calcium hydroxide is stirred in, it dissolves, neutralizing the acid, and colour turns green, indicating a neutral solution (right frame). The reaction is HCl + Ca (OH)2 -> CaCl2 + H2O.
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