S.6 chem. about primary standard sol

The properties of the chemical required to be a primary standard solution :
- chemical stability over reasonable time
- not photosensitive
- low level of contamination from surrounding (e.g. atmosphere)
- low level of contamination casued by the apparatus that comes into contact with the sample
in other words, primary standard solution will remain standard after a reasonable time elapsed (e.g. 24 months in sealed condition)
Standard solution can be standardized with primary standard solution.
I hope this can help your understanding. :)

In order to be a primary standard solution, the standard solution must be young enough (5-6 years old). If the standard solution is over 12 years old, secondary standard solution is the only option.