[Zyklonb]

Distillation will get you higher purity, but lower concentrations, 20% is easy to get. You can make some HCl gas by dropping HCl (aq) over conc. sulfuric acid. Lead the gas into your 30% solution, with an ice bath, 38% HCl (aq) can be made.

[clarkstill]

If you've got 30% and the azeotrope is 20%, can't you just distil off the azeotrope and leave behind HCl of increasing concentration?

[curiouscat]

If you've got 30% and the azeotrope is 20%, can't you just distil off the azeotrope and leave behind HCl of increasing concentration?

How can you distil it off? It's a high boiling azeotrope. It is what will remain in the still at bottom.

[Zyklonb]

If you've got 30% and the azeotrope is 20%, can't you just distil off the azeotrope and leave behind HCl of increasing concentration?

No. The HCl comes off as a gas, and it does not readily dissolve back into solution, it must be bubbled through it again. The only way to get HCl (aq) above 20% is to bubble HCl (g) through water or dilute HCl (aq). The colder you store it, the less the HCl evaporates.

[curiouscat]

If you've got 30% and the azeotrope is 20%, can't you just distil off the azeotrope and leave behind HCl of increasing concentration?

No. The HCl comes off as a gas, and it does not readily dissolve back into solution, it must be bubbled through it again. The only way to get HCl (aq) above 20% is to bubble HCl (g) through water or dilute HCl (aq). The colder you store it, the less the HCl evaporates.

Right.

And if you want to eliminate distillation add conc. H2SO4 to the 30% HCl & it will similarly drive the HCl gas out.