Primary standards
The standardization or measurement of the exact strength of a normal or other solution depends upon the use of some standard material whose purity is known, primary standards are usually salts or acid salts of high purity that can be dried at some convenient temperature without decomposing and that can be weight with a high degree of accuracy. Examples are sodium carbonate and potassium acid phthalate, which are used to standardize acid and base solutions, respectively; potassium bi iodate and potassium dichromate for reducing solutions; potassium oxalate for oxidizing solutions; and sodium chloride for solutions of silver ion. Analytical-reagent grade chemicals are usually satisfactory for most purposes. For some research purposes and possibly for referee work, analyzed primary standards mat be obtained from the U.S. National Institute of Standards and Technology.