масова частка K2 Cr2 O7

Mr(K2Cr2O7) = 39*2 + 52*2 + 16*7 = 294W(K) = Ar(K) *n / Mr(K2Cr2O7)  *100% = 39*2 / 294  *100% = 26,5%W(Cr) = Ar(Cr) * n / Mr(K2Cr2O7)  *100% = 52*2 / 294  *100% =35,4%W(O) = Ar(O) * n / Mr(K2Cr2O7)  *100% = 16*7 / 294  *100% = 39%