# Why is Borax used as a primary standard? Tags: inorganic-chemistry, titration - Score: 12 - Views: 6312 - Answers: 1 - Answered: yes - Asked by: Aditya Dev (7922 rep) - Asked: 2016-01-03 - Edited: 2016-03-21 - Site: chemistry ## Question It's given in my book that borax is a useful primary standard for titrating against acids. I have heard that primary standard is a pure reagent and does not gain any weight by absorbing moisture. (Hence any error during weight measurement is prevented). I got this from a website that came first on searching "primary standard" Primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has a high molecular weight . But borax (represented as $\ce{Na2B4O7.10H2O}$) has water of hydration. ## Answers ### Answer by A.K. (score: 13 [ACCEPTED]) Yes borax is a hydrate, but the reason it is favored for titration is that it gives consistent results, which to most scientists, is far more important than accuracy. The $\ce{ .\!10H2O}$ hydration number will remain constant and will not fluctuate to $\mathrm{11}$ or $\mathrm{9}$ within normal temperature and humidity ranges. This means that per mass the same amoun