How to titrate alkali with acid-base indicator

Methyl red indicator can be used for strong acid titration, and phenolphthalein indicator can be used for strong acid titration. For strong acid, drop weak base with methyl orange (yellow to orange) or phenolphthalein (red to colorless).

Strong alkali drops weak acid with phenolphthalein colorless to pink, note that the color change range is 8.2 (pink) ~ 10 (red).

Using acid as titrant can determine alkali, and using alkali as titrant can determine acid, which is a very widely used analytical method. The most commonly used acid standard solution is hydrochloric acid, and sometimes nitric acid and sulfuric acid are also used.

Extended data:

Because acid ions or nonmetallic ions consume part of hydrogen ions in hydrolysis and ionize hydroxyl ions, most strong alkali and weak acid salt solutions are alkaline, but there are some special cases, such as sodium bisulfite aqueous solution is acidic.

When the concentration is constant, the greater the Ka, the greater the jumping range. When Ka< is at 10-8, the indicator cannot be used to determine the end point.

When Ka is constant, the greater the acid concentration, the greater the jump. Display titration error should be; 10-8, weak acid can be directly titrated with strong base.

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