MgO
Mr(MgO)=Ar(Mg)+Ar(O)=24+16=40
w(Mg)=Ar(Mg)/Mr(MgO)=24/40=0.6=60%
w(O)=Ar(O)/Mr(MgO)=16/40=0.4=40%
Ответ: w(Mg)=60%,w(O)=40%
Al2O3
Mr(Al2O3)=Ar(Al)*2+Ar(O)*3=27*2+16*3=102
w(Al)=Ar(Al)*2/Mr(Al2O3)=54/102=0.529=53%
w(O)=Ar(O)/Mr(Al2O3)=48/102=0.470=47%
Ответ:w(Al)=53%.w(O)=47%
KMnO4
Mr(KMnO4)=Ar(К)+Ar(Mn)+Ar(O)*4=39+55+16*4=158
w(K)=Ar(K)/Mr(KMnO4)=39/158=0.246=25%
w(Mn)=Ar(Mn)/Mr(KMnO4)=55/158=0.348=35%
w(O)=Ar(O)*4/Mr(KMnO4)=64/158=0.40=40%
Ответ:w(K)=25%,w(Mn)=35%,w(O)=40%