P are A = 31
daca avem 4 moli P
=> 4x31 = 124 g P
P2O5 are M = 2x31+5x16 = 142 g/mol
=>
daca la 142 g P2O5 ................... 2x31 g P
a g P2O5 .......................... 124 g P
=> a = 124x142/62 = 284 g P2O5
