Gọi: \(\left\{{}\begin{matrix}n_{Al}=a\left(mol\right)\\n_{Zn}=b\left(mol\right)\\n_{Cu}=c\left(mol\right)\end{matrix}\right.\) ⇒ 27a + 65b + 64c = 18,3 (1)
- Cho hh pư với H2SO4.
PT: \(2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\)
\(Zn+H_2SO_4\rightarrow ZnSO_4+H_2\)
Theo PT: \(n_{H_2}=\dfrac{3}{2}n_{Al}+n_{Zn}=\dfrac{3}{2}a+b=\dfrac{8,96}{22,4}=0,4\left(mol\right)\left(2\right)\)
- Cho hh pư với không khí.
Ta có: ka + kb + kc = 0,8 (3)
PT: \(4Al+3O_2\underrightarrow{t^o}2Al_2O_3\)
\(2Zn+O_2\underrightarrow{t^o}2ZnO\)
\(2Cu+O_2\underrightarrow{t^o}2CuO\)
Theo PT: \(n_{O_2}=\dfrac{3}{4}n_{Al}+\dfrac{1}{2}n_{Zn}+\dfrac{1}{2}n_{Cu}=\dfrac{3}{4}ka+\dfrac{1}{2}kb+\dfrac{1}{2}kc=\dfrac{56}{22,4}.\dfrac{1}{5}=0,5\left(4\right)\)
Từ (3) và (4) ⇒ a - b - c = 0 (5)
Từ (1) (2) và (5) \(\Rightarrow\left\{{}\begin{matrix}a=0,2\left(mol\right)\\b=0,1\left(mol\right)\\c=0,1\left(mol\right)\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}\%m_{Al}=\dfrac{0,2.27}{18,3}.100\%\approx29,51\%\\\%m_{Zn}=\dfrac{0,1.65}{18,3}.100\%\approx35,52\%\\\%m_{Cu}\approx34,97\%\end{matrix}\right.\)