# Is "hypophosphoric acid" an "oxy-acid"?

Well, an oxyacid, is a mineral acid that contains oxygen, and $\text{hypophosphoric acid}$, like $\text{sulfuric acid}$, $\text{perchloric acid}$, and $\text{nitric acid}$ fits this description. It's been a long time since I encountered this particular customer. We would formulate $\text{hypophosphoric acid}$ as ${\left(H O\right)}_{2} \left(O =\right) P - P \left(= O\right) {\left(O H\right)}_{2}$, i.e. a species with a $P - P$ bond, and thus a formal $P \left(+ I V\right)$ oxidation state.
This site quotes $p {K}_{a 1} = 2.2$, $p {K}_{a 2} = 2.8$, $p {K}_{a 3} = 7.3$, $p {K}_{a 4} = 10.0$. The $P - P$ bond length in its salts is $2.19 \times {10}^{-} 10 \cdot m$....compare $1.88 \times {10}^{-} 10 \cdot m$ in ${P}_{4}$.