Some acids, in addition to their acid properties, have strong oxidizing ability and thus, except in very dilute solution, do not release hydrogen gas on reaction with metals. For example, nitric acid and concentrated sulfuric acid have strong oxidizing properties. Acid-base indicators are substances which have different colors in acid and basic solutions. Two common indicators are litmus which is blue in basic solution and red in acid solution, and phenolphthalein which is pink in basic solution and colorless in acid solution. Note that these indicators do not change color exactly at pH 7.
Different indicators change color at different concentrations of hydrogen ions.
When hydrogen ions react with hydroxide ions, water is formed. This reaction is called neutralization. Teacher should not permit students to taste laboratory chemicals, but should point out that the sour taste of many common foods is due to the presence of acids. Go to top . An acid is a substance that yields hydrogen ions as the only positive ions in aqueous solution.