a) Gọi số mol Mg, Al, Fe trong m gam hỗn hợp là a, b, c (mol)
\(n_{H_2}=\dfrac{7,84}{22,4}=0,35\left(mol\right)\)
PTHH: \(Mg+2HCl\rightarrow MgCl_2+H_2\uparrow\)
_______a--------------------->a------->a_______(mol)
\(2Al+6HCl\rightarrow2AlCl_3+3H_2\uparrow\)
_b-------------------->b------->1,5b___________(mol)
\(Fe+2HCl\rightarrow FeCl_2+H_2\uparrow\)
_c------------------>c------->c_______________(mol)
=> \(\left\{{}\begin{matrix}a+1,5b+c=0,35\left(1\right)\\95a+133,5b+127c=35,55\left(2\right)\end{matrix}\right.\)
Mặt khác:
PTHH: \(Mg+Cl_2\underrightarrow{t^o}MgCl_2\)
_______a--------------->a_________(mol)
\(2Al+3Cl_2\underrightarrow{t^o}2AlCl_3\)
_b----------------->b______________(mol)
\(2Fe+3Cl_2\underrightarrow{t^o}2FeCl_3\)
_c------------------>c______________(mol)
=> 95a + 133,5b + 162,5 = 39,1 (3)
(1)(2)(3) => \(\left\{{}\begin{matrix}a=0,1\left(mol\right)\\b=0,1\left(mol\right)\\c=0,1\left(mol\right)\end{matrix}\right.\)
=> m = 24.0,1 + 27.01 + 56.0,1 = 10,7(g)
b) \(\left\{{}\begin{matrix}m_{Mg}=24.0,1=2,4\left(g\right)\\m_{Al}=27.0,1=2,7\left(g\right)\\m_{Fe}=56.0,1=5,6\left(g\right)\end{matrix}\right.\)