Does hydrochloric acid change in concentration over time?

I have new bottles of 1 N hydrochloric acid from Fisher. The acid comes standardized from the company:



> 
> Standardized at 25 °C to pH 8.2 against sodium hydroxide that has been standardized against NIST™ potassium acid phthalate.
> 
> 
> 


Will it remain standardized after opening the bottle, or do we have to standardize it regularly?




First of all, check the expiry date. In general HCl solutions are secondary standards. 1 N is just a approximation. You need to standardize it every time with a primary standard such as sodium carbonate. On the other hand, constant boiling HCl is indeed a primary standard. It is not very well known, perhaps because modern analytical chemists have become lazier.


Constant-boiling hydrochloric acid
John L. Sheldon
J. Chem. Educ., 1935, 12 (8), p 377
<https://pubs.acs.org/doi/abs/10.1021/ed012p377>


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