ic , ▁meaning ▁that ▁the ▁– OH ▁group ▁can ▁lose ▁a ▁pro ton ▁ ▁leaving ▁a ▁neg atively ▁charged ▁– ▁group ▁and ▁thus ▁turning ▁the ▁acid ▁into ▁a ▁ph osph orus ▁ox o an ion . ▁ ▁Each ▁additional ▁pro ton ▁lost ▁has ▁an ▁associated ▁acid ▁dis soci ation ▁constant ▁ ▁Ka 1 , ▁Ka 2 ▁Ka 3 , ▁... , ▁often ▁expressed ▁by ▁its ▁col og arith m ▁( p K a 1 , ▁p K a 2 , ▁p K a 3 , ▁... ). ▁H ydro gen ▁atoms ▁bond ed ▁directly ▁to ▁ph osph orus ▁are ▁generally ▁not ▁acid ic . ▁ ▁Classification ▁The ▁ph osph orus ▁ox o ac ids ▁can ▁be ▁class ified ▁by ▁the ▁ox id ation ▁state ( s ) ▁of ▁the ▁ph osph orus ▁atom ( s ), ▁which ▁may ▁vary ▁from ▁+ 1 ▁to ▁+ 5 . ▁ ▁The ▁o xygen ▁atoms ▁are ▁usually ▁in ▁ox id ation ▁state ▁- 2 , ▁but ▁may ▁be ▁in ▁state ▁- 1 ▁if ▁the ▁mole c ule ▁includes ▁per ox ide ▁groups . ▁ ▁Ox id ation ▁state ▁+ 1 ▁▁ ▁Hyp oph osph orous ▁or ▁ph osph in ic ▁acid , ▁ ▁( or ▁), ▁a ▁mon op rot ic ▁acid ▁( mean ing ▁that ▁only ▁one ▁of ▁the ▁hydro gen ▁atoms ▁is ▁acid ic ). ▁ ▁Its ▁sal ts ▁and ▁est ers ▁are ▁called ▁hyp oph osph ites ▁or ▁ph osph init es . ▁ ▁Ox id ation ▁state ▁+ 3 ▁ ▁Ph osph orous