What Is a Standard Solution of Acid or Base?

In titration experiments, the standard solution is the solution of an acid or base whose concentration is accurately known. The standard solution is used to neutralize an acid or base of unknown concentration.

Standard solutions, also called titrants, are usually strong acids or bases to ensure complete chemical reactions and for sharper end points. Examples of acids used for standard solutions are hydrochloric acid, sulfuric acid and perchloric acid, all of which are used as cold dilute solutions for safety purposes. Nitric acid is not preferred for making a standard solution because it is too oxidizing and gives unwanted side reactions. Examples of bases used for standard solutions are sodium hydroxide, potassium hydroxide and barium (II) hydroxide.

The goal of carrying out acid-base titrations is to find out the concentration of an unknown solution. The titrant is gradually added to another solution of known volume and unknown concentration, also called the analyte, until the reaction reaches neutralization.

An acid-base indicator is often used to show when the reaction reaches neutralization. The indicator changes color when the pH range in a reaction changes. Examples of indicators are methyl orange, methyl red, phenol red and phenolphthalein. Choosing the appropriate indicator is important as this minimizes the titration error.