# Why is H2SO4 a good dehydrating agent while other strong acids are not?

I understand that $\ce{H2SO4}$ is a very good dehydrating agent because it is a strong acid, so that it quickly donates $\ce{H+}$ to hydroxide ions in water to form $\ce{HSO4-}$ and $\ce{H3O+}$ .But we know that there are a lot of other acids stronger than $\ce{H2SO4}$ like $\ce{HClO4}$ which are not used as dehydrating agents. They can also readily give $\ce{H+}$ to hydroxide ions in water and act as dehydrating agents but we don't use them for this purpose. Why is that?

• I dried $\ce{NiCl2 . 6 H2O}$ in a dry $\ce{HCl}$ gas stream in an inorganic lab course to give anhydrous $\ce{NiCl2}$. So yes, $\ce{HCl}$ even in gaseous form is a good dehydrating agent. – Jan Dec 6 '16 at 23:40