Question

What acid does the combination of `HNO_3 + H_2SO_4` create?

Answer 1

`"HNO"_3 + "H"_2"SO"_4 rightleftharpoons "H"_2"O" + "NO"_2^+ + "HSO"_4^-`

Explanation:

This is an acid-base reaction, with sulfuric acid (`"H"_2"SO"_4`) acting as an acid and nitric acid (`"HNO"_3`) acting as a base. After the nitric acid gets protonated, it decomposes to form a water molecule (`"H"_2"O"`) and a nitronium ion (`"NO"_2^+`). The equilibrium lies very much to the left.

This reaction is commonly a precursor to aromatic nitration.