A secondary standard solution is a chemical term that refers to a solution that has its concentration measured by titration with a primary standard solution, explains EasyChem.com. The amount of chemical reactants in the primary standard solution is known beforehand. Mathematical equations determine how many ions are in a secondary standard solution.
The main reason for making a secondary standard solution is to make one solution of an exact concentration. For instance, some substances, such as hydrochloric acid, vary concentrations with time. To make a standard hydrochloric acid solution, chemists take an approximate concentration of acid and titrate a suitable solution, such as sodium carbonate, into the hydrochloric acid. An exact concentration is then calculated after the titration is complete.
An indicator changes color marks when the titration is complete. Bromothymol blue, methyl orange or phenolphthalein are liquids that change color when a certain concentration is reached. When the titration is complete, stoichiometric calculations are used to determine the concentration of the secondary standard solution. Stoichiometry takes into account molecular weights and chemical formulas of reactants to determine mass and volume of solutions.
A primary standard solution is prepared by directly weighing the substances dissolved in a precisely measured solvent. A primary standard solution is considered pure, and the concentration of such substances are known before titration into a secondary standard solution.