1)

TN1:

2Al+2NaOH+2H_2O->2NaAlO_2+3H_2

Al_2O_3+2NaOH->2NaAlO_2+H_2O

TN2:

Mg+2HCl->MgCl_2+H_2

2Al+6HCl->2AlCl_3+3H_2

Al_2O_3+6HCl->2AlCl_3+3H_2

2)

n_{H_2}={13,44}/{22,4}=0,6(mol)

TN1 đặt n_{Mg}=x(mol);n_{Al}=y(mol);n_{Al_2O_3}=z(mol)

Theo PT: y=n_{Al}=2/3n_{H_2}=0,4(mol)

->24x+102z=32-0,4.27=21,2(1)

Ở TN2 dùng bằng nửa lượng TN1.

->n_{Mg}=0,5x(mol);n_{Al}=0,5y=0,2(mol);n_{Al_2O_3}=0,5z(mol)

Theo PT: n_{Mg}+1,5n_{Al}=n_{H_2}

->0,5x+1,5.0,2=0,6

->x=0,6(2)

(1)(2)->z=1/{15}(mol)

->\%m_{Mg}={0,6.24}/{32}.100\%=45\%

->\%m_{Al}={0,4.27}/{32}.100\%=33,75\%

->\%m_{Al_2O_3}=100-33,75-45=21,25\%