Why is phosphorous acid more acidic than phosphoric acid?
I'm pretty sure it is because phosphorus acid is more polar than phosphoric acid. This is because in the phosphoric acid there are more OHs and an O so it kind of balances out more towards the center. In phosphorus acid, there is a H on the main carbon. Hydrogen doesn't pull as much on electrons as Oxygens do and hence that part of the molecule becomes more positive causing a stronger dipole moment than that in phosphoric acid.