Gọi $n_{Al}=x(mol)$
$n_{Mg}=y(mol)$
$⇒27x+24y=24(g)(1)$
$n_{N_2O}=\frac{7,28}{22,3}=0,325(mol)$
$Al^0→Al^{+3}+3e$
x → 3x (mol)
$Mg^0→Mg^{+2}+2e$
y → 2y (mol)
$2N^{+5}+8e→N_2^{+1}$
2,6 ← 0,325 (mol)
-Bảo toàn e: ⇒ $3x+2y=2,6(2)$
Từ $(1)$ và $(2)$, ta có hệ pt:
$\left \{ {{27x+24y=24} \atop {3x+2y=2,6}} \right.$ $\left \{ {{x=0,8} \atop {y=0,1}} \right.$
-%$m_{Mg}=\frac{0,1.24}{24}.100$%$=10$%
-%$m_{Al}=100$%$-$%$m_{Mg}=100$%$-10$%$=90$%