Why are sodium hydroxide and hydrated sodium carbonate unsuitable for use as primary standards?
Sodium hydroxide cannot be used as a primary standard because of it’s hygroscopic properties as a solid. Because it is so prone to absorbing water, it is impossible to accurately measure the mass of a solid sample, so instead it must be put into solution and tritrated with a known acidic solution. This makes it a secondary standard as opposed to a primary standard. The same logic holds true for hydrated sodium carbonate. Any solution that MUST be titrated in order to know it true molarity is considered a secondary standard.
