Species Analysis in Phosphoric Acid Solution
Phosphoric acid ($H_3PO_3 $) is a binary weak acid, and the following ionization equilibrium exists in the solution:
$H_3PO_3\ rightleftharpoons H ^ ++ H_2PO_3 ^ - $
$H_2PO_3 ^ -\ rightleftharpoons H ^ ++ HPO_3 ^ {2 -} $

In Phosphoric Acid Solution, the species present are:
1. ** molecule **: $H_3PO_3 $molecule, which is an unionized phosphoric acid molecule.
2. ** cation **: $H ^ + $, produced by step ionization of phosphoric acid.
3. ** Anion **: $H_2PO_3 ^ - $, is the product of the first ionization of phosphorus; $HPO_3 ^ {2 -} $, is the anion generated by the second ionization of phosphorus.

In summary, the species in the phosphorus solution include $H_3PO_3 $, $H ^ + $, $H_2PO_3 ^ - $, $HPO_3 ^ {2 - }$ 。