Secondary Standard
A solution whose concentration has been established by titration against a primary standard.
Unit
mol/L
In depth
Substances such as sodium hydroxide absorb carbon dioxide and water from the air, so they cannot be weighed accurately and must be standardised instead. Secondary standards need periodic restandardisation because their concentration drifts during storage.
Examples in the real world
A sodium hydroxide solution standardised against potassium hydrogenphthalate before use in a titration.