Preservation of dilute standard solutions of nitric acid

Abstract

The stability of dilute standard solutions of nitric acid (M/1000 and M/200) was investigated for a period of more than two years by coulometric titration. The bottles made from soft glass, Pyrex, low-density polyethylene and Teflon, and also quartz Erlenmeyer flasks were tested as their containers of the solutions. Prior to use, these containers were filled with 1:1 nitric acid for a day and rinsed thoroughly with deionized water and then with distilled water. The concentrations of the solutions stored in polyethylene, Teflon and quartz containers did not change more than two years. A serious decreases of acidities could be found for the standard solutions stored in the soft glass containers. The decreases after about two and a half years were about 97 and 12% in M/1000 and M/200 solutions, respectively. The acidity of M/1000 solution in Pyrex bottle also decreased during long storage (about 3%/2.5 y). The main source of these decreases is attributed to neutralization of some alkaline materials from the glass containers. Teflon and quartz are advisable as the best container materials. Polyethylene bottle is also suitable for the storage of dilute standard solution of nitric acid. Amount of carbon dioxide, which permeated through the plastic containers and was absorbed by the solution, was also measured and was nearly the same as that of the equilibrium concentration of the dioxide in water or dilute acid solution exposed in air.