Acid and bases are two kinds of chemical compounds which are very useful for human beings. In daily life, acid and base compounds can be easily found. Most fruits contain acid compounds. For example, oranges or lemons contain citric acid, tomatoes contain ascorbic acid, apple contains malic acid, and grape contains tartaric acid. Stomach in human body contains hydrochloric acid which functions to kill bacteria.
Relate with the properties of acids and bases, solution can be classified into 3 groups, there are acid solution, base solution and neutral solution. Based on experience and experiment of alchemist, they are discovered the method which used to shown acid and base. That is using acid-base indicator. Acid-base indicators are color substances which show different color in acidic and basic condition.
