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how do you concentrate or distill 68 percent nitric acid to make it 90 percent or more? Answered



"A commercial grade of fuming nitric acid, referred to in the trade as "strong nitric acid" contains 90% HNO3 and has a density of 1.50 g/mL. This grade is much used in the explosives industry. It is not as volatile nor as corrosive as the anhydrous acid and has the approximate concentration of 21.4 molar."

It's sometimes used as an oxidiser in rocket/missile fuel, coupled with hydrazine hydrate for example.