# Is HNO_2 considered a strong or weak acid?

Generally, we consider strong acids to dissociate more in water than hydronium ions do. Since the $\text{pKa}$ of hydronium is about $- 1.7$, we consider strong acids to have $\text{pKa}$s below $- 1.7$. That is, they should have ${K}_{a}$ values around $100$ or above.
${\text{HNO}}_{2}$ has a ${K}_{a}$ of $4.0 \times {10}^{- 4}$, which is quite a bit less than $100$, so we consider it a weak acid.