$2KMnO4→K2MnO4+MnO2+O2$
$1/$
Chất rắn $: K2MnO4; MnO2 $
theo pt :
$nK2MnO4=nMnO4=1/2.nKMnO4=0,05mol$
$⇒m_{A}=m_{K_{2}MnO_{4}}+m_{MnO_{2}}=197.0,05+87.0,05=14,2g$
$2/$
theo pt :
$nO_{2}=1/2.n_{KMnO4}=0,05mol$
$⇒V_{O_{2}}=0,05.22,4=1,12l$
$3/$
$4Al+3O2→2Al2O3$
Chất rắn$ :Al2O3$
theo pt :
$nAl=5,4/26=0,2mol$
$⇒nAl2O3=1/2.nAl=1/2.0,2=0,1mol$
$⇒mAl2O3=0,1.102=10,2g$