CHEMISTRY COMMUNITY

For 6K5d, how do we balance the separate redox equations?
when p4->H2PO2- why do we not add H20 to both sides, how come we just directly add OH-?
Then for P4-> PH3, why don't we add 12H20 to the reactant side and 24 H20 to products then 12 OH- to reactants to balance?
aren't we usually supposed to do those steps first? ^^

For the first half reaction, you don't need H2O. Adding it would just make it end up getting canceled from both sides. For the second half reaction adding 12 to one side and 24 to the other is the same as adding just 12 to one side.

I generally add the OH- after I balance it using acidic solution then just convert the H+ to OH- (Khan academy has a good video on this) and you only really use H2O to balance oxygen you don't always need to add it.